2020 Vol. 45, No. 10
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2020, 45(10): 3509-3526.
doi: 10.3799/dqkx.2020.251
Abstract:
Mixed siliciclastic and carbonate sediment formations are widely developed and recently have become favorable petroleum exploration targets with the emergence of unconventional oil and gas plays. It becomes a research focus on continental basin, considering the complex geological conditions and various types of mixed deposition. Based on numerous exploration practices in the Bohai Bay oil field and research investigations in other parts of China and overseas, in this paper, it summarizes the main advances of the deposition of mixed sediments in continental rift basins and discusses several critical issues. The research process of continental mixed sediments can be divided into three stages:(1) infancy stage; (2) stage of rapid development; (3) stage of systematical research. There are various but no universal criteria of petrographic classifications for the mixed sediments because of different geological settings. The genetic types of mixed sediments are various and generally include proximally mixed sedimentation and distally mixed sediments, which could be further divided into 6 specific mixed types. An independent continental sedimentary facies system has been established in the Bohai Bay oil field. The mixing processes are mainly controlled by stable macroscopical tectonic setting and locally intense fault activity, arid climate and saline water, unstable siliciclastic supply of local uplift inside basin and positive paleogeomorphologic unit. Types of proximal fan-delta mixing, proximal fan-delta flank mixing, proximal braided river delta flank mixing and distal high-energy mixing could be excellent lacustrine reservoirs and are the advantageous exploration targets. At present, the relatively effective approach for predicting mixed sediment reservoirs is through investigating the paleogeographic environment and understanding the dominant geological model. Current researches on mixed sediments should be focused on the following key issues:(1) lithologic classification of mixed sediments; (2) growth habit of calcareous shell paleobiology and microbial dolomitization; (3) relationship between fine-grained mixed sediments and shale reservoirs; and (4) seismic prediction technology for mixed sediment reservoirs.
Mixed siliciclastic and carbonate sediment formations are widely developed and recently have become favorable petroleum exploration targets with the emergence of unconventional oil and gas plays. It becomes a research focus on continental basin, considering the complex geological conditions and various types of mixed deposition. Based on numerous exploration practices in the Bohai Bay oil field and research investigations in other parts of China and overseas, in this paper, it summarizes the main advances of the deposition of mixed sediments in continental rift basins and discusses several critical issues. The research process of continental mixed sediments can be divided into three stages:(1) infancy stage; (2) stage of rapid development; (3) stage of systematical research. There are various but no universal criteria of petrographic classifications for the mixed sediments because of different geological settings. The genetic types of mixed sediments are various and generally include proximally mixed sedimentation and distally mixed sediments, which could be further divided into 6 specific mixed types. An independent continental sedimentary facies system has been established in the Bohai Bay oil field. The mixing processes are mainly controlled by stable macroscopical tectonic setting and locally intense fault activity, arid climate and saline water, unstable siliciclastic supply of local uplift inside basin and positive paleogeomorphologic unit. Types of proximal fan-delta mixing, proximal fan-delta flank mixing, proximal braided river delta flank mixing and distal high-energy mixing could be excellent lacustrine reservoirs and are the advantageous exploration targets. At present, the relatively effective approach for predicting mixed sediment reservoirs is through investigating the paleogeographic environment and understanding the dominant geological model. Current researches on mixed sediments should be focused on the following key issues:(1) lithologic classification of mixed sediments; (2) growth habit of calcareous shell paleobiology and microbial dolomitization; (3) relationship between fine-grained mixed sediments and shale reservoirs; and (4) seismic prediction technology for mixed sediment reservoirs.
2020, 45(10): 3527-3542.
doi: 10.3799/dqkx.2020.154
Abstract:
In order to ascertain the genesis of the high-quality reservoirs of the Es1 in the southeast margin of the Qinnan sag, using conventional physical properties, cast thin sections, scanning electron microscope, carbon and oxygen isotopes and other analytical laboratory data, the characteristics of the Es1 in Q29, L25 and Q30 structures and the control factors of high-quality reservoirs were studied. The results show follows. (1) The tectonic background controls the type, thickness, composition and overall physical properties of the first member of Shahejie mixed rock reservoir, which is the main reason for the difference of high-quality mixed rock reservoir. The Q29 structure mainly develops mixed fans in steep slopes. Longitudinally, it is composed of cycles of fan delta with bioclastic beaches. It has the characteristics of coarse particle size, high gravel content, the highest content of medium-acid volcanic rocks in terrestrial detritus, and low quartz content. Its overall physical properties are poor, the thickness is large, the dissolution pores are dominant, and a large number of biological cavity pores are developed. The L25 structure mainly develops mixed beaches in gentle slopes. Vertically, it is composed of the interaction between fan delta and bioclastic shoal, or bioclastic shoal with fan delta. Development of dissolution pores, primary pores and a large number of biological cavity pores. The Q30 structure mainly develops bioclastic shoals in the local uplift zone under water. It has the characteristics of low content of terrestrial debris, relatively poor overall physical properties, thinnest thickness, dissolution pores and biological cavity pores. (2) Controlled by differences in different tectonic backgrounds and sedimentation, the diagenesis suffered by the Q29, L25, and Q30 structures is both similar and different. Salty lakes, strong wave elutriation, low mud content, early dolomization, containing a large amount of biological debris, the development of mud crystal cladding, and strong acidic dissolution are the common characteristics of the formation of high-quality mixed-rock reservoirs. However, the strength of atmospheric freshwater leaching, compaction, cementation, and dissolution suffered by different structures show obvious differences. (3) The mixed rock reservoir has a large lower limit of burial depth. Constrained by the factors affecting the quality of high-quality mixed rock reservoirs, searching for large-scale and medium-sized oil and gas reservoirs in large-scale steep slope zone mixed rock reservoirs and good physical properties in gentle slope zone mixed rock reservoirs is currently one of the important targets of near-middle-deep exploration in the Paleogene Bohai Sea area.
In order to ascertain the genesis of the high-quality reservoirs of the Es1 in the southeast margin of the Qinnan sag, using conventional physical properties, cast thin sections, scanning electron microscope, carbon and oxygen isotopes and other analytical laboratory data, the characteristics of the Es1 in Q29, L25 and Q30 structures and the control factors of high-quality reservoirs were studied. The results show follows. (1) The tectonic background controls the type, thickness, composition and overall physical properties of the first member of Shahejie mixed rock reservoir, which is the main reason for the difference of high-quality mixed rock reservoir. The Q29 structure mainly develops mixed fans in steep slopes. Longitudinally, it is composed of cycles of fan delta with bioclastic beaches. It has the characteristics of coarse particle size, high gravel content, the highest content of medium-acid volcanic rocks in terrestrial detritus, and low quartz content. Its overall physical properties are poor, the thickness is large, the dissolution pores are dominant, and a large number of biological cavity pores are developed. The L25 structure mainly develops mixed beaches in gentle slopes. Vertically, it is composed of the interaction between fan delta and bioclastic shoal, or bioclastic shoal with fan delta. Development of dissolution pores, primary pores and a large number of biological cavity pores. The Q30 structure mainly develops bioclastic shoals in the local uplift zone under water. It has the characteristics of low content of terrestrial debris, relatively poor overall physical properties, thinnest thickness, dissolution pores and biological cavity pores. (2) Controlled by differences in different tectonic backgrounds and sedimentation, the diagenesis suffered by the Q29, L25, and Q30 structures is both similar and different. Salty lakes, strong wave elutriation, low mud content, early dolomization, containing a large amount of biological debris, the development of mud crystal cladding, and strong acidic dissolution are the common characteristics of the formation of high-quality mixed-rock reservoirs. However, the strength of atmospheric freshwater leaching, compaction, cementation, and dissolution suffered by different structures show obvious differences. (3) The mixed rock reservoir has a large lower limit of burial depth. Constrained by the factors affecting the quality of high-quality mixed rock reservoirs, searching for large-scale and medium-sized oil and gas reservoirs in large-scale steep slope zone mixed rock reservoirs and good physical properties in gentle slope zone mixed rock reservoirs is currently one of the important targets of near-middle-deep exploration in the Paleogene Bohai Sea area.
2020, 45(10): 3543-3555.
doi: 10.3799/dqkx.2020.156
Abstract:
In order to predict the favorable lithofacies of shale fine-grained migmatite in the continental fault depressed lake basin and guide the optimization of shale oil and gas favorable targets, the sedimentary environment restoration and fine lithofacies characterization of shale fine-grained migmatite in the upper part of Es4 Formation in Dongying sag are systematically carried out by using the data of core, thin section, whole rock diffraction, element and paleontology, etc., revealing the sedimentary environment and its combination and division to the lithofacies. The results show that the depositional period of shale fine-grained migmatites in the upper part of Es4 Formation in Dongying depression is generally characterized by the transformation of climate from semi humid to humid, from bottom to top, it shows the process of increasing injection amount of clastic material source, increasing water depth, decreasing salinity and decreasing reducibility; the orderly and complex sedimentary environment controls the complexity of sedimentary fabric of shale fine-grained mixed rock to a certain extent, and then controls the diversity, combination and distribution regularity of fine-grained mixed rock facies. Based on the 4-terminal element division scheme of rock composition, sedimentary structure, calcareous structure and organic matter abundance, the shale fine-grained migmatites in the upper Es4 of Dongying depression are divided into 20 types, and the complex fine-grained migmatites are divided into different lithofacies. Under the condition of semi humid with less material source, the shallow lake strong reducing salt water environment mainly developed gypsum salt, organic laminated gypsum mudstone combined with organic laminated argillaceous limestone (dolomite) facies, while the semi deep lake strong reducing salt water environment mainly developed organic laminated microcrystalline argillaceous limestone combined with organic laminated lime mudstone frequent interbedded lithofacies. In the strong reducing and brackish water environment of the semi deep lake, there are frequent interbedded lithofacies combined with organic rich horizontal micrite and organic rich laminated limestone mudstone, while in the reducing and brackish water environment of the deep lake, there are mainly organic bedded argillaceous limestone with organic rich bedded calcareous mudstone lithofacies combination. Under the condition of moist and multi-source, the deep lake strong reducing brackish water environment mainly develops the frequent interbedded lithofacies combined with organic rich layered argillaceous limestone and organic rich layered calcareous mudstone, while the deep lake reducing brackish water environment mainly develops the organic rich layered calcareous mudstone mingled with organic rich layered argillaceous limestone lithofacies association.
In order to predict the favorable lithofacies of shale fine-grained migmatite in the continental fault depressed lake basin and guide the optimization of shale oil and gas favorable targets, the sedimentary environment restoration and fine lithofacies characterization of shale fine-grained migmatite in the upper part of Es4 Formation in Dongying sag are systematically carried out by using the data of core, thin section, whole rock diffraction, element and paleontology, etc., revealing the sedimentary environment and its combination and division to the lithofacies. The results show that the depositional period of shale fine-grained migmatites in the upper part of Es4 Formation in Dongying depression is generally characterized by the transformation of climate from semi humid to humid, from bottom to top, it shows the process of increasing injection amount of clastic material source, increasing water depth, decreasing salinity and decreasing reducibility; the orderly and complex sedimentary environment controls the complexity of sedimentary fabric of shale fine-grained mixed rock to a certain extent, and then controls the diversity, combination and distribution regularity of fine-grained mixed rock facies. Based on the 4-terminal element division scheme of rock composition, sedimentary structure, calcareous structure and organic matter abundance, the shale fine-grained migmatites in the upper Es4 of Dongying depression are divided into 20 types, and the complex fine-grained migmatites are divided into different lithofacies. Under the condition of semi humid with less material source, the shallow lake strong reducing salt water environment mainly developed gypsum salt, organic laminated gypsum mudstone combined with organic laminated argillaceous limestone (dolomite) facies, while the semi deep lake strong reducing salt water environment mainly developed organic laminated microcrystalline argillaceous limestone combined with organic laminated lime mudstone frequent interbedded lithofacies. In the strong reducing and brackish water environment of the semi deep lake, there are frequent interbedded lithofacies combined with organic rich horizontal micrite and organic rich laminated limestone mudstone, while in the reducing and brackish water environment of the deep lake, there are mainly organic bedded argillaceous limestone with organic rich bedded calcareous mudstone lithofacies combination. Under the condition of moist and multi-source, the deep lake strong reducing brackish water environment mainly develops the frequent interbedded lithofacies combined with organic rich layered argillaceous limestone and organic rich layered calcareous mudstone, while the deep lake reducing brackish water environment mainly develops the organic rich layered calcareous mudstone mingled with organic rich layered argillaceous limestone lithofacies association.
2020, 45(10): 3556-3566.
doi: 10.3799/dqkx.2020.256
Abstract:
Lacustrine carbonate and clastic mixed-deposition is developed in member 1 of Shahehjie Formation of Bohai Sea area, Bohai Bay basin. Exploration practice indicates that lacustrine mixed-deposition at deep burial depths is higher in production capacity, with proved reserves of more than 3×108 m3, since it can retain higher physical properties. In this paper, it proposes that volcanic rock basement is one of the important factors of mixed-deposition scale development, based on the geological analyses, combined with thin section, isotope, and elemental analyses, and physical simulation experiment. Volcanic rocks in the basement consist of the following three types:the Mesozoic volcanic rock basement, Paleogene volcanic rock basement, and sedimentary bodies with provenance from the volcanic rocks. Simulation experiments show that the dark minerals in the volcanic rocks in the hydrolysis process can lead to enriched metal ions in surrounding waters, and as a result, microbes arise and microbial ecological community develops, which provides conditions to enrichment of bioclastics. The discovery of dolomization filamentous cyanobacteria and globular dolomite affirms the existence of penecontemporaneous biological dolomization in mixed-deposition. Early dolomization is advantageous to the reservoir property and the late dolomization, facilitating the nucleation for later dolomization. Volcanic rock lithic fragment (gravel) internal mould pores and dissolution pores account for 10%-30% of reservoir space, with significant contribution to reservoir property. Dark mineral dissolution simulation experiments confirm that volcanic hydrolysis solution can provide Mg2+ ions, which facilitates the burial dolomization.
Lacustrine carbonate and clastic mixed-deposition is developed in member 1 of Shahehjie Formation of Bohai Sea area, Bohai Bay basin. Exploration practice indicates that lacustrine mixed-deposition at deep burial depths is higher in production capacity, with proved reserves of more than 3×108 m3, since it can retain higher physical properties. In this paper, it proposes that volcanic rock basement is one of the important factors of mixed-deposition scale development, based on the geological analyses, combined with thin section, isotope, and elemental analyses, and physical simulation experiment. Volcanic rocks in the basement consist of the following three types:the Mesozoic volcanic rock basement, Paleogene volcanic rock basement, and sedimentary bodies with provenance from the volcanic rocks. Simulation experiments show that the dark minerals in the volcanic rocks in the hydrolysis process can lead to enriched metal ions in surrounding waters, and as a result, microbes arise and microbial ecological community develops, which provides conditions to enrichment of bioclastics. The discovery of dolomization filamentous cyanobacteria and globular dolomite affirms the existence of penecontemporaneous biological dolomization in mixed-deposition. Early dolomization is advantageous to the reservoir property and the late dolomization, facilitating the nucleation for later dolomization. Volcanic rock lithic fragment (gravel) internal mould pores and dissolution pores account for 10%-30% of reservoir space, with significant contribution to reservoir property. Dark mineral dissolution simulation experiments confirm that volcanic hydrolysis solution can provide Mg2+ ions, which facilitates the burial dolomization.
2020, 45(10): 3567-3578.
doi: 10.3799/dqkx.2020.227
Abstract:
To study the dolomite origin of Shahejie Formation in Huanghekou sag, Bohai Bay basin, the petrology, morphology and isotopic geochemical characteristics of the dolomite were analyzed through core observation, thin section identification, cathodoluminescence, X-ray diffractometry (XRD), scanning electron microscopy (SEM), back-scattered electrons (BSE) and carbon and oxygen isotopes. The results show that the dolomite is yellow brown and has a lot of dissolution pores, chert and kaolinite develops. δ13C values range from -0.50‰ to 4.58‰, and δ18O values range from -14.58‰ to -2.19‰. Micritic dolomite consists of microsphere dolomite and dolomized cyanbacteria accompanied with a lot of submicron pores, sheet-like bacterial filaments and strawberry pyrite. Fibrous isopachous dolomite cements fill in the dissolution pores or grow around particle surfaces. Rhombic dolomite is dispersed in pores. During penecontemporaneous stage, sulfate reducing bacteria induced spherical dolomite precipitation. Subsequently, fibrous isopachous dolomite cements were influenced by microbes under lake floor diagenetic environment, being affected by meteoric fresh water. During shallow burial stage, rhombic dolomite precipitates by buried dolomitization. This study can provide a specific sample for microbial induced lacustrine dolomite precipitation in ancient strata and reference for exploration in the study area.
To study the dolomite origin of Shahejie Formation in Huanghekou sag, Bohai Bay basin, the petrology, morphology and isotopic geochemical characteristics of the dolomite were analyzed through core observation, thin section identification, cathodoluminescence, X-ray diffractometry (XRD), scanning electron microscopy (SEM), back-scattered electrons (BSE) and carbon and oxygen isotopes. The results show that the dolomite is yellow brown and has a lot of dissolution pores, chert and kaolinite develops. δ13C values range from -0.50‰ to 4.58‰, and δ18O values range from -14.58‰ to -2.19‰. Micritic dolomite consists of microsphere dolomite and dolomized cyanbacteria accompanied with a lot of submicron pores, sheet-like bacterial filaments and strawberry pyrite. Fibrous isopachous dolomite cements fill in the dissolution pores or grow around particle surfaces. Rhombic dolomite is dispersed in pores. During penecontemporaneous stage, sulfate reducing bacteria induced spherical dolomite precipitation. Subsequently, fibrous isopachous dolomite cements were influenced by microbes under lake floor diagenetic environment, being affected by meteoric fresh water. During shallow burial stage, rhombic dolomite precipitates by buried dolomitization. This study can provide a specific sample for microbial induced lacustrine dolomite precipitation in ancient strata and reference for exploration in the study area.
2020, 45(10): 3579-3588.
doi: 10.3799/dqkx.2020.119
Abstract:
It is the first time to find the mixed deposition of lacustrine carbonate and volcanics in Shahejie Formation, Laizhouwan sag, Bohai Sea area. The genetic mechanism of this kind of reservoir is not clear. By casting thin section, Ar-ion milling scanning electron microscope and core 3D CT scanning data, it is confirmed that the interstitial rock is a double medium storage space of pores and fractures. The lacustrine carbonate sediments were accompanied by intermittent eruptions of volcanic activities during the sedimentary period, and four kinds of mixed sedimentary modes developed. Volcanic eruptions provide a large number of tuff components which provide conditions for fluid selective dissolution. In addition, the fossils of microcodium were found in the strata, indicating that the interstitial rocks had undergone long-term exposure, and the interstitial rocks had undergone atmospheric water weathering and leaching. A large number of vertical fractures and horizontal slippage joints between low angle layers were formed in the reservoir due to tectonic action. The superposition of fractures and dissolution pores forms a fracture-pore reservoir.
It is the first time to find the mixed deposition of lacustrine carbonate and volcanics in Shahejie Formation, Laizhouwan sag, Bohai Sea area. The genetic mechanism of this kind of reservoir is not clear. By casting thin section, Ar-ion milling scanning electron microscope and core 3D CT scanning data, it is confirmed that the interstitial rock is a double medium storage space of pores and fractures. The lacustrine carbonate sediments were accompanied by intermittent eruptions of volcanic activities during the sedimentary period, and four kinds of mixed sedimentary modes developed. Volcanic eruptions provide a large number of tuff components which provide conditions for fluid selective dissolution. In addition, the fossils of microcodium were found in the strata, indicating that the interstitial rocks had undergone long-term exposure, and the interstitial rocks had undergone atmospheric water weathering and leaching. A large number of vertical fractures and horizontal slippage joints between low angle layers were formed in the reservoir due to tectonic action. The superposition of fractures and dissolution pores forms a fracture-pore reservoir.
2020, 45(10): 3589-3602.
doi: 10.3799/dqkx.2020.213
Abstract:
Mixed sediments have the dual characteristics of clastic rocks and carbonate rocks, but no effective identification method for mixed sedimentary reservoirs has been established. Based on the analysis of the development background and petrological characteristics of mixed sediments in the northern area of Liaodong Bay, the mixed sediments are divided into three types:terrigenous clastic type, biogenic carbonate type and chemical precipitated carbonate type. In addition, facies and pattern of the three types of mixed sediments are defined. Based on the cross-analysis of the physical parameters for different types, it is concluded that the biogenic carbonate type has the characteristics of medium-low to medium-high P-wave velocity, low density, and low P-wave impedance, the chemical precipitation carbonate type and terrigenous clastic type have the characteristics of medium-high P-wave, high density, and high P-wave impedance, with P-wave impedance and density as the sensitive parameters to distinguish the mixed sediments of different types. Through seismic forward modeling and real seismic data response comparison, it is found that mixed sediment strata were effected by strong low frequency energy shielding underlying buried hill formation in the area of north Liaodong Bay Shahejie Formation. In this paper, it applies an innovative matching pursuit method to the top of the buried hill to suppress strong reflection, on the basis of which lithologic sensitive parameters are predicted, effectively improving the recognition ability of the Shahejie Formation of mixed sediment strata.
Mixed sediments have the dual characteristics of clastic rocks and carbonate rocks, but no effective identification method for mixed sedimentary reservoirs has been established. Based on the analysis of the development background and petrological characteristics of mixed sediments in the northern area of Liaodong Bay, the mixed sediments are divided into three types:terrigenous clastic type, biogenic carbonate type and chemical precipitated carbonate type. In addition, facies and pattern of the three types of mixed sediments are defined. Based on the cross-analysis of the physical parameters for different types, it is concluded that the biogenic carbonate type has the characteristics of medium-low to medium-high P-wave velocity, low density, and low P-wave impedance, the chemical precipitation carbonate type and terrigenous clastic type have the characteristics of medium-high P-wave, high density, and high P-wave impedance, with P-wave impedance and density as the sensitive parameters to distinguish the mixed sediments of different types. Through seismic forward modeling and real seismic data response comparison, it is found that mixed sediment strata were effected by strong low frequency energy shielding underlying buried hill formation in the area of north Liaodong Bay Shahejie Formation. In this paper, it applies an innovative matching pursuit method to the top of the buried hill to suppress strong reflection, on the basis of which lithologic sensitive parameters are predicted, effectively improving the recognition ability of the Shahejie Formation of mixed sediment strata.
2020, 45(10): 3603-3617.
doi: 10.3799/dqkx.2020.064
Abstract:
Due to the effect of regional episodic tectonic activity, typical allogenic migrated sequence stratigraphic architecture is developed in the Shahejie Formation in Gaobei area of Nanpu sag. Based on the drilling, logging and high-resolution 3D seismic data, the characteristics and genetic mechanism of allogenic migrated sequence stratigraphic architecture are systematically studied, using structural sedimentology and sequence stratigraphy theories and methods. The results show that Shahejie Formation in the Gaobei area of Nanpu sag can be divided into three second-level sequences, which can be subdivided into seven third-level sequences(from SQ1 to SQ7). The SQ1-SQ7 sequences of Shahejie Formation present a continuous lateral stacking patterns of "see-saw" alternating thickening in the seismic profile. Among them, SQ1-SQ2 sequences are mainly developed in the west side of the basin, SQ3-SQ4 sequences are evenly developed on both sides of the basin, and SQ5-SQ7 sequences are mainly developed in the east side of the basin. Multiple factors result in this unique sequence architecture. (1) Episodic movement causes east-west differences in boundary fault activity, which leads to a large scale migration of sedimentary center from west to east.(2) The direction of the regional stress field caused by plate activities in different periods rotates clockwise, making the subsag controlling fault gradually change from the NW-SE direction in the early stage to the N-S direction.(3) Different types of fault assemblage patterns affect the location and scale of depositional center development, and thus control the migration and evolution of allogenic sequence stratigraphic architecture. In the process of lateral migration, the characteristics of sedimentary facies and filling patterns under the control of sequence stratigraphic units in different transition stages all move from west to east regularly. It is concluded that research on the genetic mechanism of allogenic migrated sequence stratigraphic architecture can provide new insights into the evolution of lacustrine rift basin sedimentary sequence under the background of episodic tectonic activity.
Due to the effect of regional episodic tectonic activity, typical allogenic migrated sequence stratigraphic architecture is developed in the Shahejie Formation in Gaobei area of Nanpu sag. Based on the drilling, logging and high-resolution 3D seismic data, the characteristics and genetic mechanism of allogenic migrated sequence stratigraphic architecture are systematically studied, using structural sedimentology and sequence stratigraphy theories and methods. The results show that Shahejie Formation in the Gaobei area of Nanpu sag can be divided into three second-level sequences, which can be subdivided into seven third-level sequences(from SQ1 to SQ7). The SQ1-SQ7 sequences of Shahejie Formation present a continuous lateral stacking patterns of "see-saw" alternating thickening in the seismic profile. Among them, SQ1-SQ2 sequences are mainly developed in the west side of the basin, SQ3-SQ4 sequences are evenly developed on both sides of the basin, and SQ5-SQ7 sequences are mainly developed in the east side of the basin. Multiple factors result in this unique sequence architecture. (1) Episodic movement causes east-west differences in boundary fault activity, which leads to a large scale migration of sedimentary center from west to east.(2) The direction of the regional stress field caused by plate activities in different periods rotates clockwise, making the subsag controlling fault gradually change from the NW-SE direction in the early stage to the N-S direction.(3) Different types of fault assemblage patterns affect the location and scale of depositional center development, and thus control the migration and evolution of allogenic sequence stratigraphic architecture. In the process of lateral migration, the characteristics of sedimentary facies and filling patterns under the control of sequence stratigraphic units in different transition stages all move from west to east regularly. It is concluded that research on the genetic mechanism of allogenic migrated sequence stratigraphic architecture can provide new insights into the evolution of lacustrine rift basin sedimentary sequence under the background of episodic tectonic activity.
2020, 45(10): 3618-3632.
doi: 10.3799/dqkx.2020.183
Abstract:
Mixed siliciclastic-carbonate sediments are widely developed in Bohai Sea area. With successive discoveries of mixed reservoir in oil exploration recently, the distribution characteristics of mixed sediments need to be addressed. Based on abundant geological data and comprehensive analyses, the time and spatial distribution characteristics of Palaeogene sediments are figured out in this study, promoting geological cognition about mixed sedimentation. Three types of E2s1-2 mixed rock in Bohai Sea area are identified as siliciclastic-dominated mixed rock, biological-carbonate-dominated mixed rock and chemical-carbonate-dominated mixed rock. Controlled by arid climate and saline water environment, the mixed sedimentation mainly develops in the first to second members of Shahejie Formation (E2s1-2) and is spatially distributed around uplift inside the basin, being far away from outside regional provenance. The favorable background of underwater positive paleotopography includes low uplift, pitching end of uplift, near-shore uplift and offshore uplift. According to development position, paleotopography setting and relationship with siliciclastic supply, the genetic pattern of mixed sedimentation could be grouped into four categories:(1) near-shore mixed fan delta; (2) near-shore mixed beach bar between fan deltas; (3) mixed beach bar on near-shore uplift; and (4) mixed beach bar on offshore uplift. Synthetic evaluation indicates that the near-shore mixed fan delta, near-shore mixed biological beach bar between fan deltas, mixed siliciclastic beach bar on near-shore uplift and mixed biological beach bar on offshore buried hill are specific favorable types of exploration since the mixed reservoir possesses large thickness and scale, coarse grains, high content of carbonate particles, less matrix and dolomite, which results in good physical properties and significant productivities. These geological cognitions have led to several discoveries of mixed reservoirs and reveal great exploration potential of mixed sediments field. The above theoretical understanding and exploration practices obtained are of great significance for promoting deep exploration in Bohai Sea area.
Mixed siliciclastic-carbonate sediments are widely developed in Bohai Sea area. With successive discoveries of mixed reservoir in oil exploration recently, the distribution characteristics of mixed sediments need to be addressed. Based on abundant geological data and comprehensive analyses, the time and spatial distribution characteristics of Palaeogene sediments are figured out in this study, promoting geological cognition about mixed sedimentation. Three types of E2s1-2 mixed rock in Bohai Sea area are identified as siliciclastic-dominated mixed rock, biological-carbonate-dominated mixed rock and chemical-carbonate-dominated mixed rock. Controlled by arid climate and saline water environment, the mixed sedimentation mainly develops in the first to second members of Shahejie Formation (E2s1-2) and is spatially distributed around uplift inside the basin, being far away from outside regional provenance. The favorable background of underwater positive paleotopography includes low uplift, pitching end of uplift, near-shore uplift and offshore uplift. According to development position, paleotopography setting and relationship with siliciclastic supply, the genetic pattern of mixed sedimentation could be grouped into four categories:(1) near-shore mixed fan delta; (2) near-shore mixed beach bar between fan deltas; (3) mixed beach bar on near-shore uplift; and (4) mixed beach bar on offshore uplift. Synthetic evaluation indicates that the near-shore mixed fan delta, near-shore mixed biological beach bar between fan deltas, mixed siliciclastic beach bar on near-shore uplift and mixed biological beach bar on offshore buried hill are specific favorable types of exploration since the mixed reservoir possesses large thickness and scale, coarse grains, high content of carbonate particles, less matrix and dolomite, which results in good physical properties and significant productivities. These geological cognitions have led to several discoveries of mixed reservoirs and reveal great exploration potential of mixed sediments field. The above theoretical understanding and exploration practices obtained are of great significance for promoting deep exploration in Bohai Sea area.
2020, 45(10): 3633-3644.
doi: 10.3799/dqkx.2020.192
Abstract:
In this paper, it conducts detailed fine-grained mixed sedimentary rocks characterization of the lower submember of Es3 by combining detailed core descriptions, microscopic observation and geochemical data, and then study on characteristics of different types of fine-grained mixed sedimentary rocks of Shahejie Formation, depositional process and evolution of lake basin in the Zhanhua depression in details. It is identified two major fine-grained mixed sedimentary rocks associations in the lower submember of Es3, including the laminar interbedding mixed sedimentary rocks association and the massive component mixed sedimentary rocks association upward, which suggests that the lake changed from larger one with stratified water column to shallower and smaller one with homogenization salinity when the paleoclimate changed from warmer and humid to cooler and drier through time. It is inferred that the accumulation of organic matter within the early and middle stage of early lacustrine high stand and middle to late lacustrine high stand was controlled by the combination of redox conditions and primary productivity, while only by primary productivity accumulation in the late stage of the early lacustrine high stand and only by redox conditions in lacustrine low stand. On the whole, the appropriate amount of terrigenous supply (clay mineral and quartz content are less than 22%) could promote the enrichment of organic matter, while excessive terrigenous input and rapid precipitation of carbonate lead to the dilution of organic matter.
In this paper, it conducts detailed fine-grained mixed sedimentary rocks characterization of the lower submember of Es3 by combining detailed core descriptions, microscopic observation and geochemical data, and then study on characteristics of different types of fine-grained mixed sedimentary rocks of Shahejie Formation, depositional process and evolution of lake basin in the Zhanhua depression in details. It is identified two major fine-grained mixed sedimentary rocks associations in the lower submember of Es3, including the laminar interbedding mixed sedimentary rocks association and the massive component mixed sedimentary rocks association upward, which suggests that the lake changed from larger one with stratified water column to shallower and smaller one with homogenization salinity when the paleoclimate changed from warmer and humid to cooler and drier through time. It is inferred that the accumulation of organic matter within the early and middle stage of early lacustrine high stand and middle to late lacustrine high stand was controlled by the combination of redox conditions and primary productivity, while only by primary productivity accumulation in the late stage of the early lacustrine high stand and only by redox conditions in lacustrine low stand. On the whole, the appropriate amount of terrigenous supply (clay mineral and quartz content are less than 22%) could promote the enrichment of organic matter, while excessive terrigenous input and rapid precipitation of carbonate lead to the dilution of organic matter.
2020, 45(10): 3645-3662.
doi: 10.3799/dqkx.2020.187
Abstract:
Mixed sediments were widely distributed in the Bohai Sea during the first and second periods of Shahejie Formation, but few were found in the third period. In this paper, taking the lower third member of Shahejie Formation of the Lainan slope belt as an example, the mixed deposit characteristics of the study area were comprehensively studied by means of various data such as wall core, thin section, drilling log and three-dimensional seismic data, etc., the distribution of mixed deposition plane and vertical direction were predicted, and the main controlling factors of the development of mixed deposition were discussed. The results show that the mixed sediments associated with lacustrine facies and volcanic eruption are developed in the lower third member of Shahejie Formation of southern slope belt of Laizhouwan sag, and that there are two types of mixed sediments associated with fractional mixing and interbedding mixing in the vertical formation. There are three types of sedimentary facies, including mixed facies, braid delta facies and pyroclastic rocks. Among them, the early continental detritus has a great influence on the development of far-shore mixed micritic beach. The influence of land-based detritus at late stage was weak, but the wave action was enhanced, and the mixed detrital beach developed. The warm and humid paleoclimate, relatively closed shallow-water environment, and the nutrients from volcanic formation during the same period provided favorable conditions for the development of mixed deposition. The supply of far source in the west and near source in the east controlled the development types of mixed deposition. Underwater paleouplift controls its plane distribution and enrichment degree. Local volcanic activities formed special mixed sedimentary lithology and its association. The results not only improve and deepen the new understanding of mixed deposition in Bohai Sea, but also provide guidance for the search for similar mixed deposition in the third member of Shahejie Formation, and also provide reference for the study of high-quality reserve utilization and well pattern deployment in the research area.
Mixed sediments were widely distributed in the Bohai Sea during the first and second periods of Shahejie Formation, but few were found in the third period. In this paper, taking the lower third member of Shahejie Formation of the Lainan slope belt as an example, the mixed deposit characteristics of the study area were comprehensively studied by means of various data such as wall core, thin section, drilling log and three-dimensional seismic data, etc., the distribution of mixed deposition plane and vertical direction were predicted, and the main controlling factors of the development of mixed deposition were discussed. The results show that the mixed sediments associated with lacustrine facies and volcanic eruption are developed in the lower third member of Shahejie Formation of southern slope belt of Laizhouwan sag, and that there are two types of mixed sediments associated with fractional mixing and interbedding mixing in the vertical formation. There are three types of sedimentary facies, including mixed facies, braid delta facies and pyroclastic rocks. Among them, the early continental detritus has a great influence on the development of far-shore mixed micritic beach. The influence of land-based detritus at late stage was weak, but the wave action was enhanced, and the mixed detrital beach developed. The warm and humid paleoclimate, relatively closed shallow-water environment, and the nutrients from volcanic formation during the same period provided favorable conditions for the development of mixed deposition. The supply of far source in the west and near source in the east controlled the development types of mixed deposition. Underwater paleouplift controls its plane distribution and enrichment degree. Local volcanic activities formed special mixed sedimentary lithology and its association. The results not only improve and deepen the new understanding of mixed deposition in Bohai Sea, but also provide guidance for the search for similar mixed deposition in the third member of Shahejie Formation, and also provide reference for the study of high-quality reserve utilization and well pattern deployment in the research area.
2020, 45(10): 3663-3676.
doi: 10.3799/dqkx.2020.223
Abstract:
The mixed deposition of terrigenous siliciclastic and lacustrine carbonates is pervasively developed in Paleogene system of Bohai Sea area. Based on drilling, sesimic, well logging and lithological testing data of 90 wells in the mixed deposition of Paleogene system of Bohai Sea area, sedimentary features and forming background were analyzed and the mixed deposition development model was established. Our research indicates that three types of sedimentary facies, including mixed fan, nearshore mixed bar, and offshore mixed bar, which could be further divided into seven types of sub facies and fourteen types of micro facies, are developed in Paleogene strata of the interest area. Nearshore mixed fan, which is normally associated with delta facies and formed near the intrabasinal local provenance of the steep slope zone, is featured with mixed deposited gully with bioclastic sandy conglomerate, and medium-coarse and medium sandstones is featured with the sedimentary facies of which is abandoned fan delta short axial source channel and bioclastic interval deposition. Nearshore mixed bar, which is generally formed near the intrabasinal local provenance of the lake bay, is featured with the mixed deposition of near source transportation sediments and intrabasinal clastic sediments. The typical sedimentary nearshore mixed bar is featured with grained clast bars of high terrigenous clastic content. Offshore mixed bar, which is developed on low uplift or isolated buried hill, is featured with rich bioclastic mixed deposits, low terrigenous clastic content, in-situ development of biology and low supply of terrigenous siliciclastics mixing. The pattern and scale of the mixed deposition are controlled by the interation of paleoclimate environment, paleotectonic activity, hydrodynamic condition, terrigenous siliciclastic supply, with the ancient landform as the most dominant factor. The establishment of the mixed depositional model could play a significant role in the future reservoir prediction and oil exploration.
The mixed deposition of terrigenous siliciclastic and lacustrine carbonates is pervasively developed in Paleogene system of Bohai Sea area. Based on drilling, sesimic, well logging and lithological testing data of 90 wells in the mixed deposition of Paleogene system of Bohai Sea area, sedimentary features and forming background were analyzed and the mixed deposition development model was established. Our research indicates that three types of sedimentary facies, including mixed fan, nearshore mixed bar, and offshore mixed bar, which could be further divided into seven types of sub facies and fourteen types of micro facies, are developed in Paleogene strata of the interest area. Nearshore mixed fan, which is normally associated with delta facies and formed near the intrabasinal local provenance of the steep slope zone, is featured with mixed deposited gully with bioclastic sandy conglomerate, and medium-coarse and medium sandstones is featured with the sedimentary facies of which is abandoned fan delta short axial source channel and bioclastic interval deposition. Nearshore mixed bar, which is generally formed near the intrabasinal local provenance of the lake bay, is featured with the mixed deposition of near source transportation sediments and intrabasinal clastic sediments. The typical sedimentary nearshore mixed bar is featured with grained clast bars of high terrigenous clastic content. Offshore mixed bar, which is developed on low uplift or isolated buried hill, is featured with rich bioclastic mixed deposits, low terrigenous clastic content, in-situ development of biology and low supply of terrigenous siliciclastics mixing. The pattern and scale of the mixed deposition are controlled by the interation of paleoclimate environment, paleotectonic activity, hydrodynamic condition, terrigenous siliciclastic supply, with the ancient landform as the most dominant factor. The establishment of the mixed depositional model could play a significant role in the future reservoir prediction and oil exploration.
2020, 45(10): 3677-3692.
doi: 10.3799/dqkx.2020.129
Abstract:
Mixed sedimentary reservoirs are widely developed in the first and second members of the Shahejie Formation in Bohai Sea, which is difficult to be identified the complex and diverse rock types. Based on the analysis of a large number of cores, sidewall cores, thin sections and whole rocks analysis, in this paper it systematically summarizes the logging characteristics of more than 10 kinds of mixed sedimentary reservoirs in six subclasses of two major types, and discusses the sensitivity of various conventional logging curves to the "composition" and "structure" of mixed sedimentary reservoir. The results show that the composition-structure two-level classification method not only has a good distinguishing effect on lithology identification but also on the quality of mixed sedimentary reservoir. Neutron and photoelectric absorption cross-section indexes are more sensitive to rock composition identification, while natural gamma, resistivity and neutron are more sensitive to rock structure identification. The logging identification method of mixed sedimentary reservoir based on composition-structure classification is simple, efficient and accurate, and has good application effect in practice. It provides insights into complex lithology identification and reservoir evaluation and classification, and has good application prospects in the lithologic identification of lacustrine migmatite reservoir in the first and second members of Shahejie Formation in Bohai Sea area and other areas under the similar geological background.
Mixed sedimentary reservoirs are widely developed in the first and second members of the Shahejie Formation in Bohai Sea, which is difficult to be identified the complex and diverse rock types. Based on the analysis of a large number of cores, sidewall cores, thin sections and whole rocks analysis, in this paper it systematically summarizes the logging characteristics of more than 10 kinds of mixed sedimentary reservoirs in six subclasses of two major types, and discusses the sensitivity of various conventional logging curves to the "composition" and "structure" of mixed sedimentary reservoir. The results show that the composition-structure two-level classification method not only has a good distinguishing effect on lithology identification but also on the quality of mixed sedimentary reservoir. Neutron and photoelectric absorption cross-section indexes are more sensitive to rock composition identification, while natural gamma, resistivity and neutron are more sensitive to rock structure identification. The logging identification method of mixed sedimentary reservoir based on composition-structure classification is simple, efficient and accurate, and has good application effect in practice. It provides insights into complex lithology identification and reservoir evaluation and classification, and has good application prospects in the lithologic identification of lacustrine migmatite reservoir in the first and second members of Shahejie Formation in Bohai Sea area and other areas under the similar geological background.
2020, 45(10): 3693-3705.
doi: 10.3799/dqkx.2020.239
Abstract:
Mixed sediment has gradually become an ideal area for deep exploration in Bohai Sea area in exploration practice. Through a large number of drilling data statistics,in this paper,it reveals the genetic conditions of mixed sediments in the Bohai Sea area. It is believed that the formation of mixed rock in Bohai Sea area is controlled by climate,water environment,provenance,paleogeomorphic conditions and sedimentary patterns. The forward modeling results show that the seismic response characteristics of the mixed rock with different thickness and different formation lithology combinations are different. Examples show that,under the constraints of the genetic environment,such as climate environment,provenance type and paleogeomorphic characteristics,it is feasible to use the combination of "genetic model to find the rule,seismic technique to trace the distribution" in the prediction of mixed sedimentary reservoirs through the combination of single well analysis,seismic facies analysis,micro-paleogeomorphology recovery,forward modeling analysis,attribute analysis and other technologies. Different key techniques of reservoir prediction for mixed type reservoirs with different thickness and lithologic combination are of significance for the exploration of mixed rock in Bohai Sea area.
Mixed sediment has gradually become an ideal area for deep exploration in Bohai Sea area in exploration practice. Through a large number of drilling data statistics,in this paper,it reveals the genetic conditions of mixed sediments in the Bohai Sea area. It is believed that the formation of mixed rock in Bohai Sea area is controlled by climate,water environment,provenance,paleogeomorphic conditions and sedimentary patterns. The forward modeling results show that the seismic response characteristics of the mixed rock with different thickness and different formation lithology combinations are different. Examples show that,under the constraints of the genetic environment,such as climate environment,provenance type and paleogeomorphic characteristics,it is feasible to use the combination of "genetic model to find the rule,seismic technique to trace the distribution" in the prediction of mixed sedimentary reservoirs through the combination of single well analysis,seismic facies analysis,micro-paleogeomorphology recovery,forward modeling analysis,attribute analysis and other technologies. Different key techniques of reservoir prediction for mixed type reservoirs with different thickness and lithologic combination are of significance for the exploration of mixed rock in Bohai Sea area.
2020, 45(10): 3706-3720.
doi: 10.3799/dqkx.2020.173
Abstract:
Mixed siliciclastic-carbonate sediments accompanied by fan-delta are well developed in the Members 1-2 of Palaeogene Shahejie Formation in the offshore Bohai Bay Basin. A study of core description,photomicrographic observation,and petrophysical properties were performed on the mixed sediment reservoirs in a lacustrine basin,attempting to unravel the depositional environment,formation mechanism,plane distribution and reservoir features of lacustrine mixed sediments. The results show that the main sub-facies within mixed fan-delta association contain mixed fan-delta front and mixed pro-fan delta. Fan-delta frontcan include mixed subaqueous debris flows genetic facies and mixed estuarine bar genetic facies. Pro-fan delta develops mixed pro-fan delta. Based on sedimentary characteristics and internal architectures of each genetic facies,the development model of mixed fan-delta siliciclastic-carbonate sediments in terrestrial rift-subsidence lacustrine basin is attributed to two aspects:the mechanism of fan-delta mixed sediments that is related to gravity driven-tractive and the mechanism of fan-delta mixed sediments that goes through a process of construction-destruction interbedding. This study characterizes the major reservoir characteristics of mixed sediments,providing insights into their advantages as a new kind of petroleum reservoir:(1) a mass of primary porosity has still been preserved in the mid-deep buried depth; (2) secondary porosities have been generated by selective dissolutions; (3) high content of carbonate content assists reservoirs acidification. This sedimentology and reservoir study is expected to facilitate future exploration in mid-deep reservoirs in the offshore Bohai Bay basin.
Mixed siliciclastic-carbonate sediments accompanied by fan-delta are well developed in the Members 1-2 of Palaeogene Shahejie Formation in the offshore Bohai Bay Basin. A study of core description,photomicrographic observation,and petrophysical properties were performed on the mixed sediment reservoirs in a lacustrine basin,attempting to unravel the depositional environment,formation mechanism,plane distribution and reservoir features of lacustrine mixed sediments. The results show that the main sub-facies within mixed fan-delta association contain mixed fan-delta front and mixed pro-fan delta. Fan-delta frontcan include mixed subaqueous debris flows genetic facies and mixed estuarine bar genetic facies. Pro-fan delta develops mixed pro-fan delta. Based on sedimentary characteristics and internal architectures of each genetic facies,the development model of mixed fan-delta siliciclastic-carbonate sediments in terrestrial rift-subsidence lacustrine basin is attributed to two aspects:the mechanism of fan-delta mixed sediments that is related to gravity driven-tractive and the mechanism of fan-delta mixed sediments that goes through a process of construction-destruction interbedding. This study characterizes the major reservoir characteristics of mixed sediments,providing insights into their advantages as a new kind of petroleum reservoir:(1) a mass of primary porosity has still been preserved in the mid-deep buried depth; (2) secondary porosities have been generated by selective dissolutions; (3) high content of carbonate content assists reservoirs acidification. This sedimentology and reservoir study is expected to facilitate future exploration in mid-deep reservoirs in the offshore Bohai Bay basin.
2020, 45(10): 3721-3730.
doi: 10.3799/dqkx.2020.175
Abstract:
QHD29-2E and Q36 structure is so far the largest fan delta siliciclastic and lacustrine carbonate mixed deposits in the first and second members of Shahejie Formation in Paleogene system of Bohai Bay area,which breaks record of maximum reserve scale of siliclastic-carbonate mixed reservoir,the maximum thickness of single oil-bearing layer,and the highest tested productivity in Bohai Sea area. In our recent research,based on comprehensive analysis of rock core,rock slice observation,carbon and oxygen isotope analysis and trace element analysis,it is found that meteoric water leaching diagenesis is the major factor for high reservoir quality forming in the mixing deposition of steep slope zone of Shijiutuo uplift. Petrographical and geochemical evidences of meteoric waters process are identified. It includes 2 processes:dissolution pores,integranular fissures,terrigenous kaolinite in conglomerates during syndepositional process,and vertical karst fissures,geopetal structure in carbonates during subaerial exposure. The meteoric leaching process could be divided into 3 stages,including provenance,transportation and beach bar periods. Finally,the meteoric diagenetic model of mixed deposits in the slope zone is established. Meteoric diagenesis takes place primarily in two formation zones:the vadose zone and the phreatic zone. The diagenetic feature and evolution model of each zone are also concluded.
QHD29-2E and Q36 structure is so far the largest fan delta siliciclastic and lacustrine carbonate mixed deposits in the first and second members of Shahejie Formation in Paleogene system of Bohai Bay area,which breaks record of maximum reserve scale of siliclastic-carbonate mixed reservoir,the maximum thickness of single oil-bearing layer,and the highest tested productivity in Bohai Sea area. In our recent research,based on comprehensive analysis of rock core,rock slice observation,carbon and oxygen isotope analysis and trace element analysis,it is found that meteoric water leaching diagenesis is the major factor for high reservoir quality forming in the mixing deposition of steep slope zone of Shijiutuo uplift. Petrographical and geochemical evidences of meteoric waters process are identified. It includes 2 processes:dissolution pores,integranular fissures,terrigenous kaolinite in conglomerates during syndepositional process,and vertical karst fissures,geopetal structure in carbonates during subaerial exposure. The meteoric leaching process could be divided into 3 stages,including provenance,transportation and beach bar periods. Finally,the meteoric diagenetic model of mixed deposits in the slope zone is established. Meteoric diagenesis takes place primarily in two formation zones:the vadose zone and the phreatic zone. The diagenetic feature and evolution model of each zone are also concluded.
2020, 45(10): 3731-3745.
doi: 10.3799/dqkx.2020.224
Abstract:
Based on the core observation,thin section identification,cathodoluminescence,oxygen-carbon isotope,and trace elements analysis,sedimemtary characteristics,controlling factors and model of mixed siliciclastic-carbonates are analyzed for finding out the spatial distribution of high-quality reservoir in the Member 1 of Paleogene Shahejie Formation in Huanghekou sag,Bohai Bay basin. The results show that it is mainly composed of carbonate and clastic rock mixed deposition and mixed layer system in the the study area. Mixed siliciclastic-carbonates of study area show cyclic change,developing section A-granular dolomitic glutenite,section B-granular dolomitic sandstone,section C-granular dolomitic (gray) rock,section D-mud dolomitic (gray) rock,and section E-shale from bottom to top. Section C is the potential reservoir with good porosity. On the plane,with the increase of the distance from the provenance area,it shows the transition from mainly mixed siliciclastic-carbonates clastic migmatite to carbonate mixed siliciclastic-carbonates. Sedimentary model of mixed siliciclastic-carbonates in the study area is built based on the analysis of controlling factors (e.g.,paleostructure,paleogeomorphology,climate,and lake level change),and it is found that the terrigenous clastic supply and climate are the main factors.
Based on the core observation,thin section identification,cathodoluminescence,oxygen-carbon isotope,and trace elements analysis,sedimemtary characteristics,controlling factors and model of mixed siliciclastic-carbonates are analyzed for finding out the spatial distribution of high-quality reservoir in the Member 1 of Paleogene Shahejie Formation in Huanghekou sag,Bohai Bay basin. The results show that it is mainly composed of carbonate and clastic rock mixed deposition and mixed layer system in the the study area. Mixed siliciclastic-carbonates of study area show cyclic change,developing section A-granular dolomitic glutenite,section B-granular dolomitic sandstone,section C-granular dolomitic (gray) rock,section D-mud dolomitic (gray) rock,and section E-shale from bottom to top. Section C is the potential reservoir with good porosity. On the plane,with the increase of the distance from the provenance area,it shows the transition from mainly mixed siliciclastic-carbonates clastic migmatite to carbonate mixed siliciclastic-carbonates. Sedimentary model of mixed siliciclastic-carbonates in the study area is built based on the analysis of controlling factors (e.g.,paleostructure,paleogeomorphology,climate,and lake level change),and it is found that the terrigenous clastic supply and climate are the main factors.
2020, 45(10): 3746-3758.
doi: 10.3799/dqkx.2020.079
Abstract:
The Pearl River Mouth basin is an important area for deep water petroleum exploration in China,within which,the Liwan X structure is mainly composed of mixed siliciclastic-carbonate sediments at the depths between 3 000 m and 3 281 m. Petrologic and isotopic geochemical characteristics were investigated by polarizing microscope and carbon-oxygen isotopic analysis. The host rock type of foraminifera and the petrographic characteristics of foraminifera mineralization were determined,and the mineralization mechanism of foraminifera was discussed,and finally the mineralization model of foraminifera was established. The bioclast of Zhujiang Formation is mainly composed of foraminiferal clasts,while the foraminiferal shell is composed of blade-,equal diameter calcite or ferrocalcite. There are mainly three filling patterns for the foraminifera's chamber:unfilled,half-filled and full-filled pattern. According to the types and the occurrences of the main authigenic minerals,the foraminiferal mineralization can be divided into four types,including pyritization,ferrocalcitization,dawsonitization and ankeritization,among which the formation of pyritization may be related to the biodegradation of foraminiferal soft tissue,and the ferrocalcitization may be related to the thermal decarboxylation of organic matter,while the magmatic CO2 provided the carbon sources for the precipitation of dawsonite and ankerite.
The Pearl River Mouth basin is an important area for deep water petroleum exploration in China,within which,the Liwan X structure is mainly composed of mixed siliciclastic-carbonate sediments at the depths between 3 000 m and 3 281 m. Petrologic and isotopic geochemical characteristics were investigated by polarizing microscope and carbon-oxygen isotopic analysis. The host rock type of foraminifera and the petrographic characteristics of foraminifera mineralization were determined,and the mineralization mechanism of foraminifera was discussed,and finally the mineralization model of foraminifera was established. The bioclast of Zhujiang Formation is mainly composed of foraminiferal clasts,while the foraminiferal shell is composed of blade-,equal diameter calcite or ferrocalcite. There are mainly three filling patterns for the foraminifera's chamber:unfilled,half-filled and full-filled pattern. According to the types and the occurrences of the main authigenic minerals,the foraminiferal mineralization can be divided into four types,including pyritization,ferrocalcitization,dawsonitization and ankeritization,among which the formation of pyritization may be related to the biodegradation of foraminiferal soft tissue,and the ferrocalcitization may be related to the thermal decarboxylation of organic matter,while the magmatic CO2 provided the carbon sources for the precipitation of dawsonite and ankerite.
2020, 45(10): 3759-3778.
doi: 10.3799/dqkx.2020.215
Abstract:
Not only are mixed rocks distributed in marine basins,but they are also distributed in a large number of hanging wall slope areas in rift sags and related to hydrocarbon accumulation closely. Mainly based on the core data and logging data of the Lixian slope,and the sedimentary characteristics and distribution of mixed beach-bars are studied through the core and thin section observation,grain size analysis,log facies analysis. Firstly,seismic data,pollen data,and trace element data were analyzed to restore the depositional environment controlling factors such as paleoclimate,paleo-provenance,paleogeomorphology,and paleo-water characteristics in the first member of Shahejie Formation. Then,the sedimentary model of the mixed beach-bars in the lower submember of the first member of Shahejie Formation in Lixian slope was systematically built. The results show that the beach-bar facies developed in the hanging wall slope area of Raoyang sag can be divided into siliciclastic beach-bars,carbonate beach-bars,and mixed beach-bars according to petrologic characteristics. Moreover,mixed beach-bars can be divided into component-mixed beach-bars and stratified-mixed beach-bars. The lithology of mixed beach-bar was mainly of calcareous sandstone,sandy oolitic limestone,and bioclastic limestone. The distribution of mixed beach-bar was controlled by factors such as paleoclimate,paleo-provenance,paleogeomorphology,and paleo-water characteristics. Therefore,different sedimentary patterns developed in different positions and different sedimentary stages on the slope. Stratified-mixed beach-bars and siliciclastic beach-bars were deposited in the near-shore ramp,and component-mixed beach-bars were deposited in the far-shore ramp. Carbonate beach-bars were mainly distributed on the far-shore low uplift.
Not only are mixed rocks distributed in marine basins,but they are also distributed in a large number of hanging wall slope areas in rift sags and related to hydrocarbon accumulation closely. Mainly based on the core data and logging data of the Lixian slope,and the sedimentary characteristics and distribution of mixed beach-bars are studied through the core and thin section observation,grain size analysis,log facies analysis. Firstly,seismic data,pollen data,and trace element data were analyzed to restore the depositional environment controlling factors such as paleoclimate,paleo-provenance,paleogeomorphology,and paleo-water characteristics in the first member of Shahejie Formation. Then,the sedimentary model of the mixed beach-bars in the lower submember of the first member of Shahejie Formation in Lixian slope was systematically built. The results show that the beach-bar facies developed in the hanging wall slope area of Raoyang sag can be divided into siliciclastic beach-bars,carbonate beach-bars,and mixed beach-bars according to petrologic characteristics. Moreover,mixed beach-bars can be divided into component-mixed beach-bars and stratified-mixed beach-bars. The lithology of mixed beach-bar was mainly of calcareous sandstone,sandy oolitic limestone,and bioclastic limestone. The distribution of mixed beach-bar was controlled by factors such as paleoclimate,paleo-provenance,paleogeomorphology,and paleo-water characteristics. Therefore,different sedimentary patterns developed in different positions and different sedimentary stages on the slope. Stratified-mixed beach-bars and siliciclastic beach-bars were deposited in the near-shore ramp,and component-mixed beach-bars were deposited in the far-shore ramp. Carbonate beach-bars were mainly distributed on the far-shore low uplift.
2020, 45(10): 3779-3796.
doi: 10.3799/dqkx.2020.167
Abstract:
Mixed fine-grained sedimentary rocks are widely developed in the shale formation of the second member of the Kongdian Formation(Ek2) in the Cangdong depression,Bohai Bay basin. A proper classification of rock types and sedimentary environment analysis of the mixed fine-grained sedimentary rocks are crucial for understanding their genesis,which is helpful to summarize the deposition law of mixed fine-grained sedimentary rocks and find favorable exploration targets. On the basis of detailed examination of cores and thin sections,XRF(X-ray fluorescence spectrometer) images,combined with XRD(X-ray diffraction),element geochemical measurement data,the mixed fine-grained sedimentary rocks in Ek2 are subdivided into 21 lithofacies based on mineral compositions and sedimentary structures. The evolution of sedimentary environments is revealed by lithofacies and changes of geochemical indexes such as Sr/Cu,Mg/Ca,Sr/Ba,V/(V+Ni),Al and Ti contents,Fe/Mn and (Fe+Al)/Ca+Mg) ratios. The mixed fine-grained sedimentary rocks in Ek2 were mainly developed under an arid climate in a semi-deep to deep lake,with brackish and anoxic water with strong terrestrial input. The lithofacies was developed under the influence of high saline water and the input of terrestrial sediments. Homogeneous fine-grained sedimentary rocks are the most widely distributed,which is followed by lime-dolomite fine-grained sedimentary rocks,while clayey fine-grained sedimentary rocks are not well developed.
Mixed fine-grained sedimentary rocks are widely developed in the shale formation of the second member of the Kongdian Formation(Ek2) in the Cangdong depression,Bohai Bay basin. A proper classification of rock types and sedimentary environment analysis of the mixed fine-grained sedimentary rocks are crucial for understanding their genesis,which is helpful to summarize the deposition law of mixed fine-grained sedimentary rocks and find favorable exploration targets. On the basis of detailed examination of cores and thin sections,XRF(X-ray fluorescence spectrometer) images,combined with XRD(X-ray diffraction),element geochemical measurement data,the mixed fine-grained sedimentary rocks in Ek2 are subdivided into 21 lithofacies based on mineral compositions and sedimentary structures. The evolution of sedimentary environments is revealed by lithofacies and changes of geochemical indexes such as Sr/Cu,Mg/Ca,Sr/Ba,V/(V+Ni),Al and Ti contents,Fe/Mn and (Fe+Al)/Ca+Mg) ratios. The mixed fine-grained sedimentary rocks in Ek2 were mainly developed under an arid climate in a semi-deep to deep lake,with brackish and anoxic water with strong terrestrial input. The lithofacies was developed under the influence of high saline water and the input of terrestrial sediments. Homogeneous fine-grained sedimentary rocks are the most widely distributed,which is followed by lime-dolomite fine-grained sedimentary rocks,while clayey fine-grained sedimentary rocks are not well developed.
2020, 45(10): 3797-3807.
doi: 10.3799/dqkx.2020.088
Abstract:
There is a set of lacustrine mixed sedimentary rocks in the first and second members of Shahejie Formation(Es1-2) in BZ27-A structure in Huanghekou sag, Bohai Sea area. At present, the research on the characteristics and genesis of this reservoir is still weak. In this study, based on the core observation, casting thin section and mercury porosimetry, the characteristics of petrology, reservoir space type, physical property of mixed sedimentary rock reservoir are systematically described firstly, and then the controlling factors of the reservoir are put forward. The results show that the mixed sedimentary rock consists of terrigenous clastic, clay minerals, carbonate minerals and biodetritus. The lithology mainly includes calcareous sandstone, dolomitic sandstone, terrigenous clastic micrite dolomite, micrite oolitic dolomite and bioclastic dolomite, which are interbeded or thin interbeded in the vertical section. Most of the mixed sedimentary rock reservoirs are tight due to low porosity and permeability, with few relatively better reservoirs in thin intervals. The main factors controlling the mixed sedimentary rock reservoirs are paleogeographic background, provenance, diagenesis and fluid. Massive carbonate cementation in the diagenetic stage is the main cause of tight reservoir, however, the contributions of bioclastic, oil and gas emplacement in the later stage of hydrocarbon accumulation are important for improving the physical properties of reservoirs, and have the potential to form relatively high-quality reservoirs.
There is a set of lacustrine mixed sedimentary rocks in the first and second members of Shahejie Formation(Es1-2) in BZ27-A structure in Huanghekou sag, Bohai Sea area. At present, the research on the characteristics and genesis of this reservoir is still weak. In this study, based on the core observation, casting thin section and mercury porosimetry, the characteristics of petrology, reservoir space type, physical property of mixed sedimentary rock reservoir are systematically described firstly, and then the controlling factors of the reservoir are put forward. The results show that the mixed sedimentary rock consists of terrigenous clastic, clay minerals, carbonate minerals and biodetritus. The lithology mainly includes calcareous sandstone, dolomitic sandstone, terrigenous clastic micrite dolomite, micrite oolitic dolomite and bioclastic dolomite, which are interbeded or thin interbeded in the vertical section. Most of the mixed sedimentary rock reservoirs are tight due to low porosity and permeability, with few relatively better reservoirs in thin intervals. The main factors controlling the mixed sedimentary rock reservoirs are paleogeographic background, provenance, diagenesis and fluid. Massive carbonate cementation in the diagenetic stage is the main cause of tight reservoir, however, the contributions of bioclastic, oil and gas emplacement in the later stage of hydrocarbon accumulation are important for improving the physical properties of reservoirs, and have the potential to form relatively high-quality reservoirs.
2020, 45(10): 3808-3826.
doi: 10.3799/dqkx.2020.127
Abstract:
It needs further study on Paleogene lacustrine fine-grained hybrid sedimentary lithofacies type, carbonate isotopic fractionation mechanism and diagenetic evolution in Dongying sag. By core observation, thin section, X-ray diffraction, carbon and oxygen isotopes and other analytical methods, it is considered to be a fine-grained in-situ mixed sedimentary rock, which can be divided into four types of lithofacies:felsic fine-grained hybrid rock and clayey fine-grained hybrid rock, carbonate fine-grained and clayey felsic fine-grained hybrid rock. The analysis of "genetic control layer" shows that the vertical changes of rock mineral composition and paleontological content reflect the supply of source, paleoclimate fluctuation and sedimentary process, which can be used as the identification mark of sequence boundary. Carbon and oxygen isotopic analysis shows that micrite calcite mainly belongs to carbonate related to biogenic gas generated by methane bacteria activity, lenticular and lamellar sparry calcite layers belong to the phenomenon of microcracks being filled by calcite veins, the general buried depth of microcracks and calcite vein formation are the early secondary dry gas generation stage, and sandstone calcite cement is closely related to the generation of mixed vein body. It is further revealed the isotopic fractionation mechanism of micrite and sparry calcite in migmatite, and the whole coevolution process from hydrocarbon generation pressurization, microfracture formation, organic matter thermal evolution to organic acid expulsion, dissolution micrite calcite and calcite recrystallization to calcite vein, which has important guiding significance for the study of shale oil and gas accumulation in middle and deep oil reservoir.
It needs further study on Paleogene lacustrine fine-grained hybrid sedimentary lithofacies type, carbonate isotopic fractionation mechanism and diagenetic evolution in Dongying sag. By core observation, thin section, X-ray diffraction, carbon and oxygen isotopes and other analytical methods, it is considered to be a fine-grained in-situ mixed sedimentary rock, which can be divided into four types of lithofacies:felsic fine-grained hybrid rock and clayey fine-grained hybrid rock, carbonate fine-grained and clayey felsic fine-grained hybrid rock. The analysis of "genetic control layer" shows that the vertical changes of rock mineral composition and paleontological content reflect the supply of source, paleoclimate fluctuation and sedimentary process, which can be used as the identification mark of sequence boundary. Carbon and oxygen isotopic analysis shows that micrite calcite mainly belongs to carbonate related to biogenic gas generated by methane bacteria activity, lenticular and lamellar sparry calcite layers belong to the phenomenon of microcracks being filled by calcite veins, the general buried depth of microcracks and calcite vein formation are the early secondary dry gas generation stage, and sandstone calcite cement is closely related to the generation of mixed vein body. It is further revealed the isotopic fractionation mechanism of micrite and sparry calcite in migmatite, and the whole coevolution process from hydrocarbon generation pressurization, microfracture formation, organic matter thermal evolution to organic acid expulsion, dissolution micrite calcite and calcite recrystallization to calcite vein, which has important guiding significance for the study of shale oil and gas accumulation in middle and deep oil reservoir.
2020, 45(10): 3827-3840.
doi: 10.3799/dqkx.2020.109
Abstract:
Lacustrine migmatite is widely distributed in the first member of Shahejie Formation of Paleogene in Bohai Sea. The bioclastic migmatite is the high-quality reservoir with good physical properties and high productivity. In this paper, a systematic paleontological study of bioclastic components in bioclastic migmatites is carried out. It is confirmed that gastropods are the most important bioclastic types in the first member of the Shahejie Formation in Bohai Sea. 21 genus and 27 species of gastropods and 19 genus and 74 species of ostracoda are identified. They are mainly miniaturized types suitable for living in a certain salinity and shallow water environment. It is found that the gastropods are easily to accumulate in high energy environment, while the content of ostracods is relatively high in low energy environment combined with paleoenvironmental studies. The analyses of casting thin section, SEM and EPMA show that bioclasts play an important role in the evolution of migmatite reservoir. The reservoir space is directly provided by the cavity hole of the bioclastic body, the mold hole of the shell, the shielding hole and the differential contraction joint. Early dissolution of bioclasts can effectively improve the permeability of the reservoir, promote dolomitization of the bioclastic enrichment section, and form a high-quality reservoir of bioclastic dolomite. Bioclasts form a stable mud crystal set with the action of microorganism, which plays a supporting role of pore lattice. The physical properties of the bioclastic migmatite mainly composed of gastropods are better than the others, as influenced by the differences of shell composition and various kinds of biological sedimentary environment.
Lacustrine migmatite is widely distributed in the first member of Shahejie Formation of Paleogene in Bohai Sea. The bioclastic migmatite is the high-quality reservoir with good physical properties and high productivity. In this paper, a systematic paleontological study of bioclastic components in bioclastic migmatites is carried out. It is confirmed that gastropods are the most important bioclastic types in the first member of the Shahejie Formation in Bohai Sea. 21 genus and 27 species of gastropods and 19 genus and 74 species of ostracoda are identified. They are mainly miniaturized types suitable for living in a certain salinity and shallow water environment. It is found that the gastropods are easily to accumulate in high energy environment, while the content of ostracods is relatively high in low energy environment combined with paleoenvironmental studies. The analyses of casting thin section, SEM and EPMA show that bioclasts play an important role in the evolution of migmatite reservoir. The reservoir space is directly provided by the cavity hole of the bioclastic body, the mold hole of the shell, the shielding hole and the differential contraction joint. Early dissolution of bioclasts can effectively improve the permeability of the reservoir, promote dolomitization of the bioclastic enrichment section, and form a high-quality reservoir of bioclastic dolomite. Bioclasts form a stable mud crystal set with the action of microorganism, which plays a supporting role of pore lattice. The physical properties of the bioclastic migmatite mainly composed of gastropods are better than the others, as influenced by the differences of shell composition and various kinds of biological sedimentary environment.
2020, 45(10): 3841-3852.
doi: 10.3799/dqkx.2020.144
Abstract:
In this study, it investigates the mixed rock reservoir of the Shahejie Formation in the steep slope of the Shijiutuo uplift in the Bohai Sea area. Through high-pressure mercury injection, two-dimensional large area back scattering scanning electron microscope imaging technology (Maps), mineral composition quantitative analysis technology (QEMSCAN) and micron CT and other experimental methods, the macro-to-micro, two-dimensional plane characteristics to three dimensional spatial characteristics and pore-throat distribution characteristics from micron to submicron in lacustrine mixed rock reservoir space of Shahejie Formation in the study area are quantitatively characterized by multi-scale analyses. According to the fractal characteristics of the pore-throat, the evaluation of the pore-throat structure of the mixed rock in the Shahejie Formation in the study area is established. The results reveal various rock types, strong heterogeneous properties and complex pore-throat structure in the lacustrine mixed rock reservoir in the study area. The millimeter-micron pore-throat network is mainly developed in high porosity, medium to high permeability bright crystalline dandruff dolomite. Dissolution pores and biological cavity holes contribute greatly to the expansion of reservoir space, the fractal dimension of pore-throat is the lowest. Submicron-micron and micron pore-throat is mainly developed in medium-high porosity, medium-low permeability dolomitic lithogenic sandstone and continental dolomite. The main storage space types are inter-granular dissolved pore, mold hole, inter-crystalline pore and so on. The pore-throat fractal dimension is medium. The pore-throat of nanometer-submicron is mainly distributed in mud crystal sand dolomite and calcareous siltstone. Inter-granular pores and micro-cracks are the main types of reservoir space. The fractal dimension of the pore throat is the highest. Multi-scale characterization and evaluation of pore-throat combination characteristics of lacustrine mixed rock reservoir provide basis for fluid identification and effective development of mixed rock reservoirs in Bohai Sea area.
In this study, it investigates the mixed rock reservoir of the Shahejie Formation in the steep slope of the Shijiutuo uplift in the Bohai Sea area. Through high-pressure mercury injection, two-dimensional large area back scattering scanning electron microscope imaging technology (Maps), mineral composition quantitative analysis technology (QEMSCAN) and micron CT and other experimental methods, the macro-to-micro, two-dimensional plane characteristics to three dimensional spatial characteristics and pore-throat distribution characteristics from micron to submicron in lacustrine mixed rock reservoir space of Shahejie Formation in the study area are quantitatively characterized by multi-scale analyses. According to the fractal characteristics of the pore-throat, the evaluation of the pore-throat structure of the mixed rock in the Shahejie Formation in the study area is established. The results reveal various rock types, strong heterogeneous properties and complex pore-throat structure in the lacustrine mixed rock reservoir in the study area. The millimeter-micron pore-throat network is mainly developed in high porosity, medium to high permeability bright crystalline dandruff dolomite. Dissolution pores and biological cavity holes contribute greatly to the expansion of reservoir space, the fractal dimension of pore-throat is the lowest. Submicron-micron and micron pore-throat is mainly developed in medium-high porosity, medium-low permeability dolomitic lithogenic sandstone and continental dolomite. The main storage space types are inter-granular dissolved pore, mold hole, inter-crystalline pore and so on. The pore-throat fractal dimension is medium. The pore-throat of nanometer-submicron is mainly distributed in mud crystal sand dolomite and calcareous siltstone. Inter-granular pores and micro-cracks are the main types of reservoir space. The fractal dimension of the pore throat is the highest. Multi-scale characterization and evaluation of pore-throat combination characteristics of lacustrine mixed rock reservoir provide basis for fluid identification and effective development of mixed rock reservoirs in Bohai Sea area.
2020, 45(10): 3853-3869.
doi: 10.3799/dqkx.2020.078
Abstract:
The mixed siliciclastic-carbonate rock reservoirs are developed in the Es12 around Bozhong depression, Bohai Sea, in which a large amount of oil and gas have been found. The reservoir physical properties show great differences, and strong heterogeneity. However, there are few studies on the differences and causes, restricting further exploration evaluation of this type of reservoir. In this paper, the differences and genesis of the high-quality reservoirs of the Es12 around Bozhong depression in Bohai Sea are discussed based on the data analyses of drilling, conventional physical properties, casting thin sections, whole rocks and clay minerals. The results show follows. (1) There are three types of reservoirs, namely bioclastic-based mixed siliciclastic-carbonate rocks, mixed siliciclastic-carbonate rocks dominated by terrigenous clastics, and mixed-rock reservoirs dominated by chemically precipitated carbonates, respectively, in Es12 around Bozhong area. A large number of snail and ostracod fossils are developed in the first two types of reservoirs. Among them, the mixed siliciclastic-carbonate rock reservoir dominated by bioclastic development has a large number of biological cavity pores, and the dolomitization has strong effect and the best physical properties. The mixed rock reservoir dominated by terrigenous clastics is mainly composed of dissolution pores, followed by biological cavity and primary pores, which is characterized by the development of mud-crystal cladding, strong dolomitization, containing a large amount of intermediate-acid volcanic rock debris, and shallow buried reservoirs have good physical properties. Calcite in cemented rock reservoirs dominated by chemical precipitation has strong cementation and poor physical properties. There are obvious differences in reservoir types and physical properties of different structural aggregate rocks. (2) The differences of mixed siliciclastic-carbonate rock reservoirs in the study area are mainly controlled by the parent rock type, basement lithology, sedimentary water environment, sedimentary facies, atmospheric freshwater leaching, buried depth compaction, cementation, dissolution and tectonic action. However, each constructed high quality reservoir has an independent combination of control factors. Non-carbonate mother rock area, the primary sedimentary period-igneous rock base, a large amount of bioclastic mixed rock, quasi-syngenetic period-atmospheric freshwater leaching, early dolomization, and deep burial period-strong dissolution, fracture development is the commonality of the formation of high-quality mixed rock reservoirs of the Es12 around Bozhong depression. The high-quality reservoir differences and genesis analysis of mixed siliciclastic-carbonate rock are important for the prediction of high-quality reservoirs in the middle and deep oil and gas exploration and evaluation process of continental fault basins.
The mixed siliciclastic-carbonate rock reservoirs are developed in the Es12 around Bozhong depression, Bohai Sea, in which a large amount of oil and gas have been found. The reservoir physical properties show great differences, and strong heterogeneity. However, there are few studies on the differences and causes, restricting further exploration evaluation of this type of reservoir. In this paper, the differences and genesis of the high-quality reservoirs of the Es12 around Bozhong depression in Bohai Sea are discussed based on the data analyses of drilling, conventional physical properties, casting thin sections, whole rocks and clay minerals. The results show follows. (1) There are three types of reservoirs, namely bioclastic-based mixed siliciclastic-carbonate rocks, mixed siliciclastic-carbonate rocks dominated by terrigenous clastics, and mixed-rock reservoirs dominated by chemically precipitated carbonates, respectively, in Es12 around Bozhong area. A large number of snail and ostracod fossils are developed in the first two types of reservoirs. Among them, the mixed siliciclastic-carbonate rock reservoir dominated by bioclastic development has a large number of biological cavity pores, and the dolomitization has strong effect and the best physical properties. The mixed rock reservoir dominated by terrigenous clastics is mainly composed of dissolution pores, followed by biological cavity and primary pores, which is characterized by the development of mud-crystal cladding, strong dolomitization, containing a large amount of intermediate-acid volcanic rock debris, and shallow buried reservoirs have good physical properties. Calcite in cemented rock reservoirs dominated by chemical precipitation has strong cementation and poor physical properties. There are obvious differences in reservoir types and physical properties of different structural aggregate rocks. (2) The differences of mixed siliciclastic-carbonate rock reservoirs in the study area are mainly controlled by the parent rock type, basement lithology, sedimentary water environment, sedimentary facies, atmospheric freshwater leaching, buried depth compaction, cementation, dissolution and tectonic action. However, each constructed high quality reservoir has an independent combination of control factors. Non-carbonate mother rock area, the primary sedimentary period-igneous rock base, a large amount of bioclastic mixed rock, quasi-syngenetic period-atmospheric freshwater leaching, early dolomization, and deep burial period-strong dissolution, fracture development is the commonality of the formation of high-quality mixed rock reservoirs of the Es12 around Bozhong depression. The high-quality reservoir differences and genesis analysis of mixed siliciclastic-carbonate rock are important for the prediction of high-quality reservoirs in the middle and deep oil and gas exploration and evaluation process of continental fault basins.
2020, 45(10): 3870-3884.
doi: 10.3799/dqkx.2020.174
Abstract:
Mixed siliciclastic-carbonate developed around Dongsha massif in early Zhujiang Formation, with the mixing types divided into compositional mixing and strata mixing. The statistic data show that the development of lithological reservoir is closely related with the distribution of mixed-sedimentation area, as 94% of the discovered lithological reservoirs are concentrated in mixed-sedimentation area. Oil and gas are accumulated in sand rocks and sealed by mud rocks or mixed rocks in lithological reservoirs.The key geological factors on lithological reservoir are studied, showing that the formation condition of lithological reservoir was controlled by terrestrial lakes, sand rocks were sourced from paleo-Pearl River, and seal rocks formed in mixed siliciclastic-carbonate sedimentation zone for its low sand ratio as the result of distal provenance, late tectonic activity and inherited structural ridges. Furthermore, integrated with oil accumulation analysis, it is suggested that lithological exploration should be focused on petroliferous sags, and centered on siliciclastic reservoirs in mixed sedimentary zone, on basis of which 3 hydrocarbon-bearing systems and 4 favorable zones are figured out in the study area.
Mixed siliciclastic-carbonate developed around Dongsha massif in early Zhujiang Formation, with the mixing types divided into compositional mixing and strata mixing. The statistic data show that the development of lithological reservoir is closely related with the distribution of mixed-sedimentation area, as 94% of the discovered lithological reservoirs are concentrated in mixed-sedimentation area. Oil and gas are accumulated in sand rocks and sealed by mud rocks or mixed rocks in lithological reservoirs.The key geological factors on lithological reservoir are studied, showing that the formation condition of lithological reservoir was controlled by terrestrial lakes, sand rocks were sourced from paleo-Pearl River, and seal rocks formed in mixed siliciclastic-carbonate sedimentation zone for its low sand ratio as the result of distal provenance, late tectonic activity and inherited structural ridges. Furthermore, integrated with oil accumulation analysis, it is suggested that lithological exploration should be focused on petroliferous sags, and centered on siliciclastic reservoirs in mixed sedimentary zone, on basis of which 3 hydrocarbon-bearing systems and 4 favorable zones are figured out in the study area.
