2017 Vol. 42, No. 4
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2017, 42(4): 485-501.
doi: 10.3799/dqkx.2017.039
Abstract:
There are many Pre-Nanhua strata and magmatic rocks in Yangtze Block, the detrital zircon preserved in sedimentary clastic rocks have great significances for limiting rock's age, tracing the source of sediments and revealing early evolution of the continent. This study is the first research of detrital zircon geochronology in both Lijiazui Formation and Luohanling Formation of Dagushi Group in the Dahongshan area, northern margin of the Yangtze block. The detrital zircons from Lijiazui Formation are dated a youngest age of 1 250±64 Ma, and several main age peaks of about 2 078 Ma, 2 437 Ma, 2 659 Ma and 3 084 Ma; the youngest age of Lijiazui Formation is 1 077±51 Ma, and it's ages peaks are about 1 126 Ma, 2 044 Ma, 2 458 Ma and 2 635 Ma. It is inferred that the sedimentary age of Lijiazui Formation is between 1 250±64 Ma and 1 126 Ma, and of Luohanling Formation is later than 1 077±51 Ma, indicating that Dagushi Group belongs to Mesoproterozoic. In addition, the age-histogram comparison of Dagushi Group and Shennongjia Goup, Kunyang Group, Dongchuan Group from different areas of Yangtze block, show that the source of these stratigraphic units are different from each other, which means the magmatic events and tectonic evolutions of each stratigraphic unit are different. Combined with previous research data of Yangtze block, we conclude that the blocks represented by each stratigraphic units are independent continent fragments in Mesoproterozoic, and amalgamated into the crystalline basement of the Yangtze block gradually in Mesoproterozoic to Neoproterozoic.
There are many Pre-Nanhua strata and magmatic rocks in Yangtze Block, the detrital zircon preserved in sedimentary clastic rocks have great significances for limiting rock's age, tracing the source of sediments and revealing early evolution of the continent. This study is the first research of detrital zircon geochronology in both Lijiazui Formation and Luohanling Formation of Dagushi Group in the Dahongshan area, northern margin of the Yangtze block. The detrital zircons from Lijiazui Formation are dated a youngest age of 1 250±64 Ma, and several main age peaks of about 2 078 Ma, 2 437 Ma, 2 659 Ma and 3 084 Ma; the youngest age of Lijiazui Formation is 1 077±51 Ma, and it's ages peaks are about 1 126 Ma, 2 044 Ma, 2 458 Ma and 2 635 Ma. It is inferred that the sedimentary age of Lijiazui Formation is between 1 250±64 Ma and 1 126 Ma, and of Luohanling Formation is later than 1 077±51 Ma, indicating that Dagushi Group belongs to Mesoproterozoic. In addition, the age-histogram comparison of Dagushi Group and Shennongjia Goup, Kunyang Group, Dongchuan Group from different areas of Yangtze block, show that the source of these stratigraphic units are different from each other, which means the magmatic events and tectonic evolutions of each stratigraphic unit are different. Combined with previous research data of Yangtze block, we conclude that the blocks represented by each stratigraphic units are independent continent fragments in Mesoproterozoic, and amalgamated into the crystalline basement of the Yangtze block gradually in Mesoproterozoic to Neoproterozoic.
2017, 42(4): 502-510.
doi: 10.3799/dqkx.2017.040
Abstract:
Tadong Group of Jilin Province is known for large-scale magnetite ore deposit, and Tadong iron deposit is the largest submarine volcano plume-metamorphic-reformation iron deposit in the Jilin-Heilongjiang metallogenic province. Complicated of geological characteristics and geological processes made the ownership of Tadong Group long been controversial. In this paper, the U-Pb zircon ages of the biotite plagioclase gneiss and magnetite diopside plagioclase leptynite are obtained by LA-ICP-MS. Zircons that obtained from biotite plagioclase gneiss are prismatic, and Th/U range between 0.17 and 0.65. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 517.6±2.7 Ma, indicating the formation age of the vocanic. In the magnetite diopside plagioclase leptynite, there are two kinds of zircons with two age groups, respectively. The first kind of zircons are short columns, and Th/U range between 0.78 and 1.00. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 249.8±4.0 Ma, indicating the age of thermal disturbance. Another kind of zircons are subhedral short prismatic, and have extremely high U, Th contents, the highest Th contents is 17 422 μg/g, respectively. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 518.3±3.8 Ma, attributing to the age of hydrothermal event. It is indicated that there is a hydrothermal process at 518.3 Ma or so, which might be related to magmatism. Iron mineralization of Tadong iron deposit of Jilin Province is most likely related with this hydrothermal event. Therefore, one of mineralizations happened in the Early Cambrian Period (±520 Ma) in Tadong iron deposit.
Tadong Group of Jilin Province is known for large-scale magnetite ore deposit, and Tadong iron deposit is the largest submarine volcano plume-metamorphic-reformation iron deposit in the Jilin-Heilongjiang metallogenic province. Complicated of geological characteristics and geological processes made the ownership of Tadong Group long been controversial. In this paper, the U-Pb zircon ages of the biotite plagioclase gneiss and magnetite diopside plagioclase leptynite are obtained by LA-ICP-MS. Zircons that obtained from biotite plagioclase gneiss are prismatic, and Th/U range between 0.17 and 0.65. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 517.6±2.7 Ma, indicating the formation age of the vocanic. In the magnetite diopside plagioclase leptynite, there are two kinds of zircons with two age groups, respectively. The first kind of zircons are short columns, and Th/U range between 0.78 and 1.00. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 249.8±4.0 Ma, indicating the age of thermal disturbance. Another kind of zircons are subhedral short prismatic, and have extremely high U, Th contents, the highest Th contents is 17 422 μg/g, respectively. U-Pb dating of these zircons record 206Pb/238U weighted mean age of 518.3±3.8 Ma, attributing to the age of hydrothermal event. It is indicated that there is a hydrothermal process at 518.3 Ma or so, which might be related to magmatism. Iron mineralization of Tadong iron deposit of Jilin Province is most likely related with this hydrothermal event. Therefore, one of mineralizations happened in the Early Cambrian Period (±520 Ma) in Tadong iron deposit.
2017, 42(4): 511-526.
doi: 10.3799/dqkx.2017.041
Abstract:
Further research on the lithospheric mantle beneath western North China craton is significant in order to understand the degree and evolution of its thinning and transformation thoroughly. Mantle peridotite xenoliths in the Cenozoic alkaline basalts from Jining of western North China craton provide important constraints on the nature and evolution of the lithospheric mantle beneath this area. The samples were analyzed by using LA-ICP-MS and LA-MC-ICP-MS to obtain major element, trace element and Sr isotopic compositions. According to the mineral composition, the peridotites were classified into two groups: (1) Clinopyroxene (Cpx)-poor peridotites (Cpx < 8%), which might have experienced high-degree partial melting, suggest relict of old and refractory lithospheric mantle under this area. (2) lherzolites (Cpx > 13%). They might have experienced low-degree partial melting, representing the fertilized lithospheric mantle. Cpx grains in Type 1 peridotite have relatively low REE contents and show slightly LREE-enriched patterns, while Cpx grains in Type 2 peridotite show both LREE-enriched and slightly LREE-depleted REE patterns. Most Cpx grains show core-rim variations in strong incompatible elements and Sr isotopic compositions. These features indicate that the peridotites could have experienced metamorphism. Variations of (La/Yb)N and Ti/Eu ratios imply multistage metasomatism, which could have been caused by silicate and carbonatite melts/fluids associated with the Paleo-Asian oceanic plate subduction.
Further research on the lithospheric mantle beneath western North China craton is significant in order to understand the degree and evolution of its thinning and transformation thoroughly. Mantle peridotite xenoliths in the Cenozoic alkaline basalts from Jining of western North China craton provide important constraints on the nature and evolution of the lithospheric mantle beneath this area. The samples were analyzed by using LA-ICP-MS and LA-MC-ICP-MS to obtain major element, trace element and Sr isotopic compositions. According to the mineral composition, the peridotites were classified into two groups: (1) Clinopyroxene (Cpx)-poor peridotites (Cpx < 8%), which might have experienced high-degree partial melting, suggest relict of old and refractory lithospheric mantle under this area. (2) lherzolites (Cpx > 13%). They might have experienced low-degree partial melting, representing the fertilized lithospheric mantle. Cpx grains in Type 1 peridotite have relatively low REE contents and show slightly LREE-enriched patterns, while Cpx grains in Type 2 peridotite show both LREE-enriched and slightly LREE-depleted REE patterns. Most Cpx grains show core-rim variations in strong incompatible elements and Sr isotopic compositions. These features indicate that the peridotites could have experienced metamorphism. Variations of (La/Yb)N and Ti/Eu ratios imply multistage metasomatism, which could have been caused by silicate and carbonatite melts/fluids associated with the Paleo-Asian oceanic plate subduction.
2017, 42(4): 527-548.
doi: 10.3799/dqkx.2017.042
Abstract:
In order to discuss the tectonic evolution of the Xing-Meng orogenic belt during the Late Palaeozoic, this study conducts a systematic study of the chronology, geochemical compositions and Hf isotopic characteristics of the quartz diorite, granodiorite and biotite granite from the south of Xiwuqi, which is situated at the southern margin of the southern Mongolian terrane. Zircon U-Pb dating indicates that the quartz diorite, granodiorite and biotite granite were emplaced at ca. 330±2 Ma, 274±1 Ma and 271±1 Ma~282±1 Ma, respectively. The quartz diorite shows typical features of HMA and may be formed by melting of the subcontinental lithospheric mantle wedge induced by fluids released from partial melting of the subducted oceanic crust. The source of the studied granodiorite and biotite granite might be related to partial melting of juvenile crustal materials. Considering the regional geology, we infer that the Late Palaeozoic intrusions from the south of Xiwuqi were likely emplaced during the northward subduction of the Paleo-Asian Ocean plate beneath the southern Mongolian terrane. The Early Carboniferous quartz diorites are components of a continental arc-related magmatism, the Early Perrmian granodiorites and biotite granites are products of magmatism in a temporal back-arc extension setting during the northward subduction.
In order to discuss the tectonic evolution of the Xing-Meng orogenic belt during the Late Palaeozoic, this study conducts a systematic study of the chronology, geochemical compositions and Hf isotopic characteristics of the quartz diorite, granodiorite and biotite granite from the south of Xiwuqi, which is situated at the southern margin of the southern Mongolian terrane. Zircon U-Pb dating indicates that the quartz diorite, granodiorite and biotite granite were emplaced at ca. 330±2 Ma, 274±1 Ma and 271±1 Ma~282±1 Ma, respectively. The quartz diorite shows typical features of HMA and may be formed by melting of the subcontinental lithospheric mantle wedge induced by fluids released from partial melting of the subducted oceanic crust. The source of the studied granodiorite and biotite granite might be related to partial melting of juvenile crustal materials. Considering the regional geology, we infer that the Late Palaeozoic intrusions from the south of Xiwuqi were likely emplaced during the northward subduction of the Paleo-Asian Ocean plate beneath the southern Mongolian terrane. The Early Carboniferous quartz diorites are components of a continental arc-related magmatism, the Early Perrmian granodiorites and biotite granites are products of magmatism in a temporal back-arc extension setting during the northward subduction.
2017, 42(4): 549-558.
doi: 10.3799/dqkx.2017.043
Abstract:
The East Ordos basin is the hotpoint in recent years. In order to supply boundary conditions for field stress numerical simulation and fractures prediction in the eastern Ordos basin, this paper focus on the study of the specific parameters of the field stress between Late Jurassic and Early Cretaceous of Upper Paleozoic in eastern Ordos basin. Based on the retrieving of the syntectonicstructural deformation, calculatingof denudation thickness and the analyzing of the mudstone compaction curve, this paper got the triaxial stress state, the maximum horizontal principal stress direction, and the additive tectonic stress, the vertical earth stress, in-situ stress and differential stress. The results show that, the maximum and minimum principal stress were nearly horizontalwith the direction of the former point to SEE98°. The intermediate principal stress was nearly vertical. The triaxial stresses and the differential stress, which were get from Upper Paleozoic, located in 93.2 to 101.3 MPa, 65.8 to 67.2 MPa, 53.1 to 53.6 MPa and 40.1 to 48.0 MPa respectively. Those results providesignificant basis for field stress numerical simulation, fractures prediction as well as the optimization of favorable exploration zones in the fracturedreservoir.
The East Ordos basin is the hotpoint in recent years. In order to supply boundary conditions for field stress numerical simulation and fractures prediction in the eastern Ordos basin, this paper focus on the study of the specific parameters of the field stress between Late Jurassic and Early Cretaceous of Upper Paleozoic in eastern Ordos basin. Based on the retrieving of the syntectonicstructural deformation, calculatingof denudation thickness and the analyzing of the mudstone compaction curve, this paper got the triaxial stress state, the maximum horizontal principal stress direction, and the additive tectonic stress, the vertical earth stress, in-situ stress and differential stress. The results show that, the maximum and minimum principal stress were nearly horizontalwith the direction of the former point to SEE98°. The intermediate principal stress was nearly vertical. The triaxial stresses and the differential stress, which were get from Upper Paleozoic, located in 93.2 to 101.3 MPa, 65.8 to 67.2 MPa, 53.1 to 53.6 MPa and 40.1 to 48.0 MPa respectively. Those results providesignificant basis for field stress numerical simulation, fractures prediction as well as the optimization of favorable exploration zones in the fracturedreservoir.
2017, 42(4): 559-569.
doi: 10.3799/dqkx.2017.044
Abstract:
The Geologic structure of Erlian basin has been controversial. To make clear the developmental periods of inversion structure and their genetic dynamic mechanism of Bayindulan sag, Erlian basin in Early Cretaceous, we make use of the new processing of 3D seismic data covering the all sag to identify the important tectonic unconformity interfaces and to make sure the contact relationship between the strata developed in Early Cretaceous. Combined the igneous rock revealing in drilling data, we think that the late 3rd Member of K1ba Formation, and the late 4th member of K1ba Formation, the late K1bt1, and the late K1bt2 mainly all developed normal inversion structures. The further studies indicate that the four positive inversion structures in the Early Cretaceous were caused by the developing magmatic diapiric structure under the setting of the regional extensional stress field; while inversion structure in early K1bt2 was typically caused by the regional strike-slip movement. Therefore, the genetic mechanisms of various inversion structures developed in different periods are dissimilar, which was closely coordinated with the subduction of Paleo-Pacific plate to Eurasia, the effects of the magmatic diapiric caused by the metasomatic mantle and regional strike-slip action resulted by the change of subduction direction of Paleo-Pacific plate during the Early Cretaceous period.
The Geologic structure of Erlian basin has been controversial. To make clear the developmental periods of inversion structure and their genetic dynamic mechanism of Bayindulan sag, Erlian basin in Early Cretaceous, we make use of the new processing of 3D seismic data covering the all sag to identify the important tectonic unconformity interfaces and to make sure the contact relationship between the strata developed in Early Cretaceous. Combined the igneous rock revealing in drilling data, we think that the late 3rd Member of K1ba Formation, and the late 4th member of K1ba Formation, the late K1bt1, and the late K1bt2 mainly all developed normal inversion structures. The further studies indicate that the four positive inversion structures in the Early Cretaceous were caused by the developing magmatic diapiric structure under the setting of the regional extensional stress field; while inversion structure in early K1bt2 was typically caused by the regional strike-slip movement. Therefore, the genetic mechanisms of various inversion structures developed in different periods are dissimilar, which was closely coordinated with the subduction of Paleo-Pacific plate to Eurasia, the effects of the magmatic diapiric caused by the metasomatic mantle and regional strike-slip action resulted by the change of subduction direction of Paleo-Pacific plate during the Early Cretaceous period.
2017, 42(4): 570-586.
doi: 10.3799/dqkx.2017.045
Abstract:
BZ34-9 area and KL6 area are located in the north and south of Laibei low uplift, respectively in south of Bohai Sea. The characteristics of the sandstone reservoirs in the two areas are of great differences in spite of the similar background of Cenozoic basalt development which has been proven by drilling. The contrastive studies on structural background, temporal-spacial distribution of basalt, sedimentary system and reservoir development have been taken combined with the analytical methods of 3-D seismic data, well log, casting thin section observation, SEM, BSE and X-ray diffraction. For the BZ34-9 area, braided river deltas were deposited on a gentle slope at low depositional rates. Syndepositional basalt flows occur in the upper and lower parts of the sand body and high-quality sandstone reservoirs are characterized by dolomite coats, zeolite cementation and dissolution, and mixed-layer clay coats, which collectively had a positive impact on the reservoir quality.By contrast, the KL6 area was situated on a steep slope and fan delta deposition occurred at a high rate. The Neogene basalt focused on the middle of the basin and had limited influence on the sandstone reservoirs which is characterized by abundant kaolinite and carbonate cementation. The Oligocene strata of KL6 area which situated near Tan-Lu fault zone has been greatly influenced by the Neogene basalt activities during the diagenesis stages. The magma and hydrothermal activity caused recrystallization of siderite, sericitization and prevailing precipitation of ferrodolomite. The basalt influence on the sandstone reservoirs are controlled by the time of eruption, source supply and the configuration of sandbody and basalt.
BZ34-9 area and KL6 area are located in the north and south of Laibei low uplift, respectively in south of Bohai Sea. The characteristics of the sandstone reservoirs in the two areas are of great differences in spite of the similar background of Cenozoic basalt development which has been proven by drilling. The contrastive studies on structural background, temporal-spacial distribution of basalt, sedimentary system and reservoir development have been taken combined with the analytical methods of 3-D seismic data, well log, casting thin section observation, SEM, BSE and X-ray diffraction. For the BZ34-9 area, braided river deltas were deposited on a gentle slope at low depositional rates. Syndepositional basalt flows occur in the upper and lower parts of the sand body and high-quality sandstone reservoirs are characterized by dolomite coats, zeolite cementation and dissolution, and mixed-layer clay coats, which collectively had a positive impact on the reservoir quality.By contrast, the KL6 area was situated on a steep slope and fan delta deposition occurred at a high rate. The Neogene basalt focused on the middle of the basin and had limited influence on the sandstone reservoirs which is characterized by abundant kaolinite and carbonate cementation. The Oligocene strata of KL6 area which situated near Tan-Lu fault zone has been greatly influenced by the Neogene basalt activities during the diagenesis stages. The magma and hydrothermal activity caused recrystallization of siderite, sericitization and prevailing precipitation of ferrodolomite. The basalt influence on the sandstone reservoirs are controlled by the time of eruption, source supply and the configuration of sandbody and basalt.
2017, 42(4): 587-600.
doi: 10.3799/dqkx.2017.046
Abstract:
In order to deepen the understanding of magmatic activity characteristics in North Yellow Sea basin, discuss the tectonic origin of such intensified magmatic activity in Early Cretaceous, and reveal the structural dynamic mechanism in eastern China, the magmatic activity characteristics and its coupling relationship with regional tectonics were well depicted in North Yellow Sea basin based on well data, high-precision 3D seismic data and magmatic rocks test data. On the space scale, intrusive and extrusive characteristics of magmatic rocks on the seismic profiles and the lateral distribution along the major faults of magmatic rocks were described specifically. On the time scale, four stages of magmatic activity were recognized including 108-115 Ma and 134-145 Ma which occurred in Early Cretaceous. When combined the magmatic activity with regional geological analysis, we believed that magmatic activity exceptionally fierce in the early period of Early Cretaceous. At that time, Izanagi plate oblique dived beneath the Eurasian plate along the NNW with high-speed and low angle. At the same time, the Pacific plate dived in SW. Under the plate shearing action, the Tanlu fault zone started to sinistral strike-slip which generated the sinistral stretching environment around North Yellow Sea basin. Therefore, the derived NW dextral and SN sinistral secondary conjugate fault systems inside the basin controlled the intrusion of magmatic diapir activity. After a comprehensive analysis, the coupling relationship between magmatic activity, fault evolution characteristics, and regional plate movement had been confirmed.
In order to deepen the understanding of magmatic activity characteristics in North Yellow Sea basin, discuss the tectonic origin of such intensified magmatic activity in Early Cretaceous, and reveal the structural dynamic mechanism in eastern China, the magmatic activity characteristics and its coupling relationship with regional tectonics were well depicted in North Yellow Sea basin based on well data, high-precision 3D seismic data and magmatic rocks test data. On the space scale, intrusive and extrusive characteristics of magmatic rocks on the seismic profiles and the lateral distribution along the major faults of magmatic rocks were described specifically. On the time scale, four stages of magmatic activity were recognized including 108-115 Ma and 134-145 Ma which occurred in Early Cretaceous. When combined the magmatic activity with regional geological analysis, we believed that magmatic activity exceptionally fierce in the early period of Early Cretaceous. At that time, Izanagi plate oblique dived beneath the Eurasian plate along the NNW with high-speed and low angle. At the same time, the Pacific plate dived in SW. Under the plate shearing action, the Tanlu fault zone started to sinistral strike-slip which generated the sinistral stretching environment around North Yellow Sea basin. Therefore, the derived NW dextral and SN sinistral secondary conjugate fault systems inside the basin controlled the intrusion of magmatic diapir activity. After a comprehensive analysis, the coupling relationship between magmatic activity, fault evolution characteristics, and regional plate movement had been confirmed.
2017, 42(4): 601-612.
doi: 10.3799/dqkx.2017.047
Abstract:
As the only one basin which oil has come to the industrial standard in Tibet, it is believed that the Lunpola basin extend into rich-oil area, but exploration and investigation activities were limited, so that the development of Niubao Formation, palaeogene, is not clear, which not only limited the evaluation of oil and gas, but also the exploration strategy. Based on the drilling, logging and related laboratory test data, an integrated approach involving the logging regression equation model and basin modeling technique was used to investigate the distribution of source rock, organic matter abundance and types in main period of Niubao Formation, and to reconstruct the source rock thermal evolution history, so an evaluation system for source rocks was presented in Lunpola basin. The following conclusions can be drawn: the Lunpola basin is riched by the source rocks of Niubao Formation, and the middle of the second member of Niubao Formation is widely distributed with large thickness, the date indicates that the source rock thickness in Jiangriacuo sag can reach above 400 m, what's more, the thickness of excellent source rocks (TOC > 1.0%) can reach more than 170 m; in general, the type of source rocks of Niubao Formation is good, with highest proportion of good-excellent source rock in the upper of the second member of Niubao Formation and lower proportion in the middle of the second member of Niubao Formation; parent material types of source rocks in Niubao Formation are mainly mixed type of type Ⅱ1-Ⅰ and have oil-prone characteristic; the maturities of organic matters are mainly high in the midwest and low in the east, the results indicate that the middle of the second member of Niubao Formation is middle and late mature, the upper of the second member of Niubao Formation and the bottom of the third member of Niubao Formation are immature to early mature to present-day. Therefore, in Lunpola basin, the middle of the second member of Niubao Formation is major source rock and Jiangriacuo sag is the most important hydrocarbon generating sag.
As the only one basin which oil has come to the industrial standard in Tibet, it is believed that the Lunpola basin extend into rich-oil area, but exploration and investigation activities were limited, so that the development of Niubao Formation, palaeogene, is not clear, which not only limited the evaluation of oil and gas, but also the exploration strategy. Based on the drilling, logging and related laboratory test data, an integrated approach involving the logging regression equation model and basin modeling technique was used to investigate the distribution of source rock, organic matter abundance and types in main period of Niubao Formation, and to reconstruct the source rock thermal evolution history, so an evaluation system for source rocks was presented in Lunpola basin. The following conclusions can be drawn: the Lunpola basin is riched by the source rocks of Niubao Formation, and the middle of the second member of Niubao Formation is widely distributed with large thickness, the date indicates that the source rock thickness in Jiangriacuo sag can reach above 400 m, what's more, the thickness of excellent source rocks (TOC > 1.0%) can reach more than 170 m; in general, the type of source rocks of Niubao Formation is good, with highest proportion of good-excellent source rock in the upper of the second member of Niubao Formation and lower proportion in the middle of the second member of Niubao Formation; parent material types of source rocks in Niubao Formation are mainly mixed type of type Ⅱ1-Ⅰ and have oil-prone characteristic; the maturities of organic matters are mainly high in the midwest and low in the east, the results indicate that the middle of the second member of Niubao Formation is middle and late mature, the upper of the second member of Niubao Formation and the bottom of the third member of Niubao Formation are immature to early mature to present-day. Therefore, in Lunpola basin, the middle of the second member of Niubao Formation is major source rock and Jiangriacuo sag is the most important hydrocarbon generating sag.
2017, 42(4): 613-624.
doi: 10.3799/dqkx.2017.048
Abstract:
Concealed fault zones are a type of weak deformation fault zones that form in sedimentary covers and have expressive forms of faults that show in the early-middle stage of their formation and evolution processes. It can be found by reservoirs, sedimentary facies, sags (depressions) and ridges ranged regularly. Concealed fault zones are supposed to be potential direction for future exploration since reservoirs are usually distributed in concealed fault zones, displaying en-echelon, string or belt patterns. On the vacant area of concealed fault zones should be worthy of oil and gas exploration area in the future According to the scale, concealed fault zones are classified into 5 types in this paper: (1) the trap scale concealed fault zone consists of a series of en echelon fault blocks, curved blocks or compound blocks in line; (2) the sub-sag scale concealed fault zone composed of a lot of faults and folds, with the distribution of echelons and string of many small faults; (3) the sag scale concealed fault zone showing that there is an intermittent string of sub-sags, ridges, sedimentary facies or traps; (4) the depression scale concealed fault zone identified by the mutation of basement depth, the thickness of the sedimentary cover and sedimentary facies, belonging to regional-concealed fault; (5) the basin scale concealed fault zone characterized by large-scale nosing folds or low-amplitude ridges ranged in defined rows. In addition, the evolution model of concealed fault is established under the evolution of transtensional regional stress field and basement fault activities combined with the structural analogue experiments. It is found that concealed fault zones have controlled the accumulation of the oil and gas in the following six patterns: en echelon fault block accumulation pattern, banded fault block accumulation pattern, en echelon fold accumulation pattern, an accumulation pattern of parallel combination traps, an accumulationpattern of grid combination traps, an accumulation pattern of circularity combination traps.
Concealed fault zones are a type of weak deformation fault zones that form in sedimentary covers and have expressive forms of faults that show in the early-middle stage of their formation and evolution processes. It can be found by reservoirs, sedimentary facies, sags (depressions) and ridges ranged regularly. Concealed fault zones are supposed to be potential direction for future exploration since reservoirs are usually distributed in concealed fault zones, displaying en-echelon, string or belt patterns. On the vacant area of concealed fault zones should be worthy of oil and gas exploration area in the future According to the scale, concealed fault zones are classified into 5 types in this paper: (1) the trap scale concealed fault zone consists of a series of en echelon fault blocks, curved blocks or compound blocks in line; (2) the sub-sag scale concealed fault zone composed of a lot of faults and folds, with the distribution of echelons and string of many small faults; (3) the sag scale concealed fault zone showing that there is an intermittent string of sub-sags, ridges, sedimentary facies or traps; (4) the depression scale concealed fault zone identified by the mutation of basement depth, the thickness of the sedimentary cover and sedimentary facies, belonging to regional-concealed fault; (5) the basin scale concealed fault zone characterized by large-scale nosing folds or low-amplitude ridges ranged in defined rows. In addition, the evolution model of concealed fault is established under the evolution of transtensional regional stress field and basement fault activities combined with the structural analogue experiments. It is found that concealed fault zones have controlled the accumulation of the oil and gas in the following six patterns: en echelon fault block accumulation pattern, banded fault block accumulation pattern, en echelon fold accumulation pattern, an accumulation pattern of parallel combination traps, an accumulationpattern of grid combination traps, an accumulation pattern of circularity combination traps.
2017, 42(4): 625-633.
doi: 10.3799/dqkx.2017.049
Abstract:
The AHP method is one of the key technologies in predicting coal seam floor water inrush. But, the traditional AHP method, which is based on 1-9 scale, often has some problems. For example, the consistency effect is not ideal. Therefore, through the research on these problems, the technique of the improved AHP vulnerable index method, which is based on 10/10-18/2 scale, was put forward. Then, the vulnerability evaluation of the No. 3, 9 and 15 coal in Chengzhuang coalmine was taken as an example. Firstly, based on the establishment of the thematic layers diagrams of eight main factors, the weight of each main factors was determined using the improved AHP method. Then, the vulnerability evaluation model of the floor water inrush from the Ordovician limestone aquifer was constructed. Finally, the vulnerability zoning of each part in the study area of the No.3, 9 and 15 coal mine were obtained. The results showed that the judgment matrix constructed by the improved AHP method has better consistency effect. Furthermore, compared with the results of the traditional water inrush coefficient method, the results of the improved AHP vulnerability index method, which can truly reflect the nonlinear dynamic process of the floor water inrush under multi-factor affection, are more consistent with the actual.
The AHP method is one of the key technologies in predicting coal seam floor water inrush. But, the traditional AHP method, which is based on 1-9 scale, often has some problems. For example, the consistency effect is not ideal. Therefore, through the research on these problems, the technique of the improved AHP vulnerable index method, which is based on 10/10-18/2 scale, was put forward. Then, the vulnerability evaluation of the No. 3, 9 and 15 coal in Chengzhuang coalmine was taken as an example. Firstly, based on the establishment of the thematic layers diagrams of eight main factors, the weight of each main factors was determined using the improved AHP method. Then, the vulnerability evaluation model of the floor water inrush from the Ordovician limestone aquifer was constructed. Finally, the vulnerability zoning of each part in the study area of the No.3, 9 and 15 coal mine were obtained. The results showed that the judgment matrix constructed by the improved AHP method has better consistency effect. Furthermore, compared with the results of the traditional water inrush coefficient method, the results of the improved AHP vulnerability index method, which can truly reflect the nonlinear dynamic process of the floor water inrush under multi-factor affection, are more consistent with the actual.
2017, 42(4): 634-640.
doi: 10.3799/dqkx.2017.050
Abstract:
The initial soil moisture content distribution was one of the important factors that affect the moving down of wetting front. Traditional rainfall infiltration model only assumed that the initial moisture content was uniform and the situation of non-uniform was not taking into consideration. Based on the Mein-Larson rainfall infiltration model, this paper deduced a new landslide rainfall infiltration function by assuming the initial moisture content distribution linear with the increase of perpendicular to the direction of slope surface depth. It made up for the original model that only applied to the situation of uniforminitial moisture content distribution. The result showed that the initial moisture content distribution had large effect on the moving downof wetting front. In the case of initial moisture content was linear distribution, the greater the slope surface moisture content, the value of k which was the one of fitting parameters was closer to the zero, the faster the wetting front infiltrated. When the value of k equaled to the zero, the new model changed to the Mein-Larson rainfall infiltration model. It proved that the Mein-Larson rainfall infiltration model was a special case of the new model. Compared with the result of FEM, the results of the calculation model agree with that of FEM. It proved the reliability of the new model.
The initial soil moisture content distribution was one of the important factors that affect the moving down of wetting front. Traditional rainfall infiltration model only assumed that the initial moisture content was uniform and the situation of non-uniform was not taking into consideration. Based on the Mein-Larson rainfall infiltration model, this paper deduced a new landslide rainfall infiltration function by assuming the initial moisture content distribution linear with the increase of perpendicular to the direction of slope surface depth. It made up for the original model that only applied to the situation of uniforminitial moisture content distribution. The result showed that the initial moisture content distribution had large effect on the moving downof wetting front. In the case of initial moisture content was linear distribution, the greater the slope surface moisture content, the value of k which was the one of fitting parameters was closer to the zero, the faster the wetting front infiltrated. When the value of k equaled to the zero, the new model changed to the Mein-Larson rainfall infiltration model. It proved that the Mein-Larson rainfall infiltration model was a special case of the new model. Compared with the result of FEM, the results of the calculation model agree with that of FEM. It proved the reliability of the new model.
2017, 42(4): 641-644.
doi: 10.3799/dqkx.2017.051
Abstract:
The highly accurate detecting technology of deeply refined oil pipelines has been used FDEM (frequency domain electromagnetic method) method in the subway shield construction site. We summary that how to improve detecting accuracy of refined oil pipelines for about 16 m buried depth. First step, we determine the direction Y of the target pipeline and narrow the searching area through detecting working of X direction on ground. With background interfere the error of pipeline's location is not acceptable and depth error is large when using two different working frequencies on ground detection. Second step, we need detect the direction Z of two boreholes with the distance at 5.0 m from target pipeline. And we can acquire Hz measured curve of the target pipeline nearby. Last step, measured and theoretical Hz curves is inverted and acquired high accurate results with location and depth is 20 cm and 10 cm. It can provide accurate and basic technical data for subway construction. The way of detecting Z direction of borehole can avoid the inference of X direction on ground and also provide a way to test the result of ground detecting. The method is worth popularizing to the acceptance of the quality of ground detection. The signal processing technology of detection dates will be widely used in detecting underground pipeline base on FDEM method with its powerful advance and superiority.
The highly accurate detecting technology of deeply refined oil pipelines has been used FDEM (frequency domain electromagnetic method) method in the subway shield construction site. We summary that how to improve detecting accuracy of refined oil pipelines for about 16 m buried depth. First step, we determine the direction Y of the target pipeline and narrow the searching area through detecting working of X direction on ground. With background interfere the error of pipeline's location is not acceptable and depth error is large when using two different working frequencies on ground detection. Second step, we need detect the direction Z of two boreholes with the distance at 5.0 m from target pipeline. And we can acquire Hz measured curve of the target pipeline nearby. Last step, measured and theoretical Hz curves is inverted and acquired high accurate results with location and depth is 20 cm and 10 cm. It can provide accurate and basic technical data for subway construction. The way of detecting Z direction of borehole can avoid the inference of X direction on ground and also provide a way to test the result of ground detecting. The method is worth popularizing to the acceptance of the quality of ground detection. The signal processing technology of detection dates will be widely used in detecting underground pipeline base on FDEM method with its powerful advance and superiority.
2017, 42(4): 645-651.
doi: 10.3799/dqkx.2017.052
Abstract:
Three component rotational ground motion is one of the most important point of geophysics research. In this paper, the rotational ground motions with three components were deduced by calculation using records of translational seismographs from explosions. The observational data used are from three shots with explosive charge of 500 kg for each and observational distances of 1.8, 2.8, 8.9 km respectively. The rotational motions of the array from these three shots were obtained by calculation. The largest peak angular velocities of ground motion are 41.65, 21.98 and 0.29 μrads/s respectively, which are quite near the results from international colleagues. How the peak values of the ground motion decay with the epicenter distance is always the focal problem in earthquake engineering. In this paper, the peak angular velocities of ground motion are fit with exponent function, and the decay of peak values with distance is obtained. The main features of the decay curves are as follows: The values decay very fast within 1-3 km and slow down gradually beyond 5 km. And with the increase of the distance, the curve tends to more and more flat.
Three component rotational ground motion is one of the most important point of geophysics research. In this paper, the rotational ground motions with three components were deduced by calculation using records of translational seismographs from explosions. The observational data used are from three shots with explosive charge of 500 kg for each and observational distances of 1.8, 2.8, 8.9 km respectively. The rotational motions of the array from these three shots were obtained by calculation. The largest peak angular velocities of ground motion are 41.65, 21.98 and 0.29 μrads/s respectively, which are quite near the results from international colleagues. How the peak values of the ground motion decay with the epicenter distance is always the focal problem in earthquake engineering. In this paper, the peak angular velocities of ground motion are fit with exponent function, and the decay of peak values with distance is obtained. The main features of the decay curves are as follows: The values decay very fast within 1-3 km and slow down gradually beyond 5 km. And with the increase of the distance, the curve tends to more and more flat.
2017, 42(4): 652-660.
doi: 10.3799/dqkx.2017.053
Abstract:
The research about tight gas sandstones is one the forefront research. In order to characterize rock electrical properties in tight gas sandstones of different diagenetic facies in Taiyuan Formation, Dingbei Area, we conducted casting thin sections, porosity and permeability, micro-CT and high pressure mercury intrusion/withdrawal method on these sandstones. Four diagenetic facies are observed in the area, namely, quartz cementation diagenetic facies, kaolinite partially filled diagenetic facies, unstable components resolution diagenetic facies and tight compaction diagenetic facies. The formation factor shows very good relationship with porosity regardless of diagenetic facies, hence a and m are set constant at 15.88 and 0.82 for all the diagenetic facies. Saturation exponent (n) are variable among the different diagenetic facies, 2.30, 1.51, 2.03 and 4.04 are selected repectively for the n value of the four diagenetic facies. Examples show that the chosen electrical parameters have good agreements with the gas production test, much better than the result of chosen the theoretical n value of 2.
The research about tight gas sandstones is one the forefront research. In order to characterize rock electrical properties in tight gas sandstones of different diagenetic facies in Taiyuan Formation, Dingbei Area, we conducted casting thin sections, porosity and permeability, micro-CT and high pressure mercury intrusion/withdrawal method on these sandstones. Four diagenetic facies are observed in the area, namely, quartz cementation diagenetic facies, kaolinite partially filled diagenetic facies, unstable components resolution diagenetic facies and tight compaction diagenetic facies. The formation factor shows very good relationship with porosity regardless of diagenetic facies, hence a and m are set constant at 15.88 and 0.82 for all the diagenetic facies. Saturation exponent (n) are variable among the different diagenetic facies, 2.30, 1.51, 2.03 and 4.04 are selected repectively for the n value of the four diagenetic facies. Examples show that the chosen electrical parameters have good agreements with the gas production test, much better than the result of chosen the theoretical n value of 2.
