2017 Vol. 42, No. 3
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2017, 42(3): 315-324.
doi: 10.3799/dqkx.2017.024
Abstract:
Resources in eastern Arctic are quite abundant, however, a number of problems exist due to complicated regional geological structure and low degree of exploration. In this paper, the structure diagram of the study area is compiled, and the regional geological structure and its evolution are presented on the basis of a large collection of regional geological documents. The main tectonic units in the area include Verkhoyansk-Kolyma orogen, microplate of Arctic Alaska-Chukotka, Kolyma-Omolon superterrane, and South Anyui suture. As the open of Amerasia basin in Early Jurassic to Early Cretaceous, the microplate of Arctic Alaska-Chukotka rifted from the north margin of Canada. With the close of the Anui-Anvil (Angayucham) ocean, Alaska-Chukotka microplate collided with Kolyma-Omolon superterrane, resulting in the formation of South Anyui suture. Moreover, Verkhoyansk-Kolyma orogen resulted from collision between Verkhoyansk margin of Siberia continent and Kolyma-Omolon superterrane.
Resources in eastern Arctic are quite abundant, however, a number of problems exist due to complicated regional geological structure and low degree of exploration. In this paper, the structure diagram of the study area is compiled, and the regional geological structure and its evolution are presented on the basis of a large collection of regional geological documents. The main tectonic units in the area include Verkhoyansk-Kolyma orogen, microplate of Arctic Alaska-Chukotka, Kolyma-Omolon superterrane, and South Anyui suture. As the open of Amerasia basin in Early Jurassic to Early Cretaceous, the microplate of Arctic Alaska-Chukotka rifted from the north margin of Canada. With the close of the Anui-Anvil (Angayucham) ocean, Alaska-Chukotka microplate collided with Kolyma-Omolon superterrane, resulting in the formation of South Anyui suture. Moreover, Verkhoyansk-Kolyma orogen resulted from collision between Verkhoyansk margin of Siberia continent and Kolyma-Omolon superterrane.
2017, 42(3): 339-356.
doi: 10.3799/dqkx.2017.026
Abstract:
The Gangjiang Copper-Molybdenum deposit is a typical porphyry deposit, which locates in the Central Gangdese metallogenic belt. In order to determine the ages of magmatism and mineralization, and disentangle the complicated magmatic evolution and the relationship between magmatic process and copper-molybdenum mineralization, the author carried out a study of LA-ICP-MS zircon U-Pb ages of the monzogranite porphyry, granodiorite porphyry, and tonalite porphyrite in Gangjiang mining area. It is shown that the zircon U-Pb weighted isochron ages are 16.6±0.3 Ma (MSWD=0.94, n=10), 16.1±0.2 Ma (MSWD=1.07, n=12), 14.4±0.4 Ma (MSWD=1.12, n=7). Meanwhile, twelve molybdenite samples separated from quartz sulfides in Gangjiang copper orebodies were used for Re-Os dating, and the model ages obtained range from 13.24±0.20 Ma to 13.55±0.22 Ma, with weighted average 13.4±0.1 Ma (MSWD=0.65) and isochron age 13.6±1.6 Ma (MSWD=1.2). On the basis of geological studies, and conbined with the results mentioned above and previous research data, it is proposed that the rock mass intrusion sequence is monzogranite porphyry→granodiorite porphyry→tonalite porphyrite→rhyolite porphyry. The porphyry occurred ranges from 16.6 Ma to 14.4 Ma, and the mineralization age of Gangjiang deposit is about 13.4 Ma, and petrogenetic and metallogenic is a continuous process of magmatic evolution. The Re content of the molybdenite is 155.4-171.1 μg/g, with an average of 162.9 μg/g, suggesting that the metallogenic material originated from a source with mantle components. Gangjiang porphyry copper-molybdenum deposit was formed in post-collisional extension setting of India-Asia continental collision orogenic belt during the Miocene.
The Gangjiang Copper-Molybdenum deposit is a typical porphyry deposit, which locates in the Central Gangdese metallogenic belt. In order to determine the ages of magmatism and mineralization, and disentangle the complicated magmatic evolution and the relationship between magmatic process and copper-molybdenum mineralization, the author carried out a study of LA-ICP-MS zircon U-Pb ages of the monzogranite porphyry, granodiorite porphyry, and tonalite porphyrite in Gangjiang mining area. It is shown that the zircon U-Pb weighted isochron ages are 16.6±0.3 Ma (MSWD=0.94, n=10), 16.1±0.2 Ma (MSWD=1.07, n=12), 14.4±0.4 Ma (MSWD=1.12, n=7). Meanwhile, twelve molybdenite samples separated from quartz sulfides in Gangjiang copper orebodies were used for Re-Os dating, and the model ages obtained range from 13.24±0.20 Ma to 13.55±0.22 Ma, with weighted average 13.4±0.1 Ma (MSWD=0.65) and isochron age 13.6±1.6 Ma (MSWD=1.2). On the basis of geological studies, and conbined with the results mentioned above and previous research data, it is proposed that the rock mass intrusion sequence is monzogranite porphyry→granodiorite porphyry→tonalite porphyrite→rhyolite porphyry. The porphyry occurred ranges from 16.6 Ma to 14.4 Ma, and the mineralization age of Gangjiang deposit is about 13.4 Ma, and petrogenetic and metallogenic is a continuous process of magmatic evolution. The Re content of the molybdenite is 155.4-171.1 μg/g, with an average of 162.9 μg/g, suggesting that the metallogenic material originated from a source with mantle components. Gangjiang porphyry copper-molybdenum deposit was formed in post-collisional extension setting of India-Asia continental collision orogenic belt during the Miocene.
2017, 42(3): 357-377.
doi: 10.3799/dqkx.2017.027
Abstract:
Gravity flow deposits of Laiyang Group at the lower part of Lingshan island attract an increasing attention of geologists at home and abroad because of its huge thickness and unique sedimentary features. However, its weathering degree, characteristics and structural setting of provenance, and depositional environment stillremain in dispute. In this study, major elements, rare earth elements and trace elements contents of the siltstones from Laiyang Group at Lingshan Island were examined by XRF and ICP-MS. It is found that siltstones are characterized by relatively low contents of SiO2 (avg. 51.78%) and high contents of Fe2O3T (avg. 51.78%); average contents of Na2O and K2O of siltstones are 2.74% and 2.79%, respectively, the siltstones are classified as litharenites and greywackes; ΣREE contents of the samples are 153.00×10-6-254.38×10-6 (avg. 201.65×10-6), which are higher than those of UCC and PAAS; the pattern of REE is characterized by LREE enrichment, HREE depletion, moderately negative Eu abnormity and weakly negative Ce abnormity; compared with UCC, samples are enriched in LILEs, weakly enriched in HFSEs and depleted in transitional elements. Index of Compositional Variability (ICV) values of siltstones in Lingshan Island are high, which indicates the source materials are mainly primary cycle sediments, Chemical Index of Alteration (CIA) values are relatively low, which suggests that the weathering intensity of provenance is low. Element analysis indicates that felsic rocks serve as the main source rocks, including small amounts of contributions from recycled orogenic belt materials; tectonic settings of provenance belong to active continental margin and continental island arc; sedimentary environment is reducing marine environment and paleoclimate of Laiyang Period was arid. It is original for the authors to apply the statistical analysis method to determine the provenance regions more precisely according to the features of REEs, and it is concluded that the source rocks are most likely from Jiaonan Group and Penglai Group.
Gravity flow deposits of Laiyang Group at the lower part of Lingshan island attract an increasing attention of geologists at home and abroad because of its huge thickness and unique sedimentary features. However, its weathering degree, characteristics and structural setting of provenance, and depositional environment stillremain in dispute. In this study, major elements, rare earth elements and trace elements contents of the siltstones from Laiyang Group at Lingshan Island were examined by XRF and ICP-MS. It is found that siltstones are characterized by relatively low contents of SiO2 (avg. 51.78%) and high contents of Fe2O3T (avg. 51.78%); average contents of Na2O and K2O of siltstones are 2.74% and 2.79%, respectively, the siltstones are classified as litharenites and greywackes; ΣREE contents of the samples are 153.00×10-6-254.38×10-6 (avg. 201.65×10-6), which are higher than those of UCC and PAAS; the pattern of REE is characterized by LREE enrichment, HREE depletion, moderately negative Eu abnormity and weakly negative Ce abnormity; compared with UCC, samples are enriched in LILEs, weakly enriched in HFSEs and depleted in transitional elements. Index of Compositional Variability (ICV) values of siltstones in Lingshan Island are high, which indicates the source materials are mainly primary cycle sediments, Chemical Index of Alteration (CIA) values are relatively low, which suggests that the weathering intensity of provenance is low. Element analysis indicates that felsic rocks serve as the main source rocks, including small amounts of contributions from recycled orogenic belt materials; tectonic settings of provenance belong to active continental margin and continental island arc; sedimentary environment is reducing marine environment and paleoclimate of Laiyang Period was arid. It is original for the authors to apply the statistical analysis method to determine the provenance regions more precisely according to the features of REEs, and it is concluded that the source rocks are most likely from Jiaonan Group and Penglai Group.
2017, 42(3): 378-388.
doi: 10.3799/dqkx.2017.028
Abstract:
The Ziyunshan peraluminous granite, located in central Jiangxi Province is closely related to uranium and tungsten mineralization. In order to obtain the accurate age of this granite, the electron microscope, SEM and EMPA were firstly used to study uraninites in the Ziyunshan granite in this study. Results show that most of the uraninites are wrapped in biotite or muscovitized biotite, and only one is surrounded by pyrite. Some uraninite grains have been fractured or altered, which indicates uraninite is one of the most important uranium source minerals of granite type uranium deposits in this area. Five uraninite grains electron microprobe U-Th-Pb dating results in the Jiaokeng unit (J3J) are between 154.5 Ma and 168.9 Ma, the weighted average age is 161.8±2.4 Ma (MSWD=0.26, n=26). Chemical ages of three uraninite grains in the Miaoqian unit (J3M) are between 152.8 Ma and 164.7 Ma, the weighted average age is 159.7±3.2 Ma (MSWD=0.2, n=15). Chemical ages obtained here are very consistent with W-bearing granites in the South China. It is confirmed that uraninite EMPA chemical dating is a suitable method for U-fertile peraluminous granites.
The Ziyunshan peraluminous granite, located in central Jiangxi Province is closely related to uranium and tungsten mineralization. In order to obtain the accurate age of this granite, the electron microscope, SEM and EMPA were firstly used to study uraninites in the Ziyunshan granite in this study. Results show that most of the uraninites are wrapped in biotite or muscovitized biotite, and only one is surrounded by pyrite. Some uraninite grains have been fractured or altered, which indicates uraninite is one of the most important uranium source minerals of granite type uranium deposits in this area. Five uraninite grains electron microprobe U-Th-Pb dating results in the Jiaokeng unit (J3J) are between 154.5 Ma and 168.9 Ma, the weighted average age is 161.8±2.4 Ma (MSWD=0.26, n=26). Chemical ages of three uraninite grains in the Miaoqian unit (J3M) are between 152.8 Ma and 164.7 Ma, the weighted average age is 159.7±3.2 Ma (MSWD=0.2, n=15). Chemical ages obtained here are very consistent with W-bearing granites in the South China. It is confirmed that uraninite EMPA chemical dating is a suitable method for U-fertile peraluminous granites.
2017, 42(3): 389-396.
doi: 10.3799/dqkx.2017.029
Abstract:
The dolomite formation problem has been puzzling geologists for a long time. Recently, microbial mediation is becoming one leading theory for dolomite formation, though many details still remain poorly understood. The exclusive occurrence of modern dolomite in saline environments leads to the investigation of the role of halophiles in dolomite formation. In this study, we focus on the effect of salinity and cell concentrations on dolomite mineralization with three halophilic archaea, Natrinema sp.J7-1, Natrinema sp.J7-3 and Natrinema sp.LJ7. These halophilic archaea were collected and subject to the mineral phase identification, morphology observation and element analysis via X-ray Diffraction (XRD) and Scanning Electronic Microscopy equipped with Energy Dispersive Spectrum (EDS). Results confirm that all the strains used are capable of facilitating the dolomite formation under higher salinity conditions, and the yields of dolomite increase with cell concentration. Morphologically, dolomite is of the shape of sphere, dumb-bell, cauliflower and conglobulation. It is proposed that high salinity and high cell density will result in the more carboxyl groups on cell surface which can serve as nucleation sites for dolomite formation, which is favorable for dolomite formation. The results offer more details about microbial role in dolomite formation and enhance our understanding about the mechanism.
The dolomite formation problem has been puzzling geologists for a long time. Recently, microbial mediation is becoming one leading theory for dolomite formation, though many details still remain poorly understood. The exclusive occurrence of modern dolomite in saline environments leads to the investigation of the role of halophiles in dolomite formation. In this study, we focus on the effect of salinity and cell concentrations on dolomite mineralization with three halophilic archaea, Natrinema sp.J7-1, Natrinema sp.J7-3 and Natrinema sp.LJ7. These halophilic archaea were collected and subject to the mineral phase identification, morphology observation and element analysis via X-ray Diffraction (XRD) and Scanning Electronic Microscopy equipped with Energy Dispersive Spectrum (EDS). Results confirm that all the strains used are capable of facilitating the dolomite formation under higher salinity conditions, and the yields of dolomite increase with cell concentration. Morphologically, dolomite is of the shape of sphere, dumb-bell, cauliflower and conglobulation. It is proposed that high salinity and high cell density will result in the more carboxyl groups on cell surface which can serve as nucleation sites for dolomite formation, which is favorable for dolomite formation. The results offer more details about microbial role in dolomite formation and enhance our understanding about the mechanism.
2017, 42(3): 397-409.
doi: 10.3799/dqkx.2017.030
Abstract:
Volcanic reservoirs and oil & gas shows have been found worldwide. However, the modelling of volcanic rocks related hydrocarbon accumulation process shows little progress due to strong volcanic reservoir heterogeneity. Using PetroMod software, gas migration and accumulation in the volcanic reservoirs has been successfully modelled for the first time in this study. Three dimensional geological modelling, key parameters or methods selection are described in detail. Based on the statistical porosity of volcanic rocks, the relationship of porosity versus depth for volcanic rocks was established using an exponential model, then the gas migration and accumulation processes under different situations, such as fault activity periods and flow simulation methods, were modelled. The results show that gas generation from organic matter in the study area has a long period in a relay mode without major gas generation period; volcanic gas reservoirs formed mainly during Quantou-Qingshankou Formation end period, and gas reservoir distributions were controlled by fault locations, activity periods, volcanic rock mass and porosities; the fault activity time is before 94.5 Ma indicated by simulation results. It is concluded that the integrated migration method is the best way for describing gas migration in the volcanic rocks. Slope zone, micro-structures in the sag, lithologic pinchout and volcanic mass are favorable zones for the volcanic gas exploration in the study area, meanwhile, the tight conglomerate or tight sand in the deep formation should also have a great potential for gas exploration.
Volcanic reservoirs and oil & gas shows have been found worldwide. However, the modelling of volcanic rocks related hydrocarbon accumulation process shows little progress due to strong volcanic reservoir heterogeneity. Using PetroMod software, gas migration and accumulation in the volcanic reservoirs has been successfully modelled for the first time in this study. Three dimensional geological modelling, key parameters or methods selection are described in detail. Based on the statistical porosity of volcanic rocks, the relationship of porosity versus depth for volcanic rocks was established using an exponential model, then the gas migration and accumulation processes under different situations, such as fault activity periods and flow simulation methods, were modelled. The results show that gas generation from organic matter in the study area has a long period in a relay mode without major gas generation period; volcanic gas reservoirs formed mainly during Quantou-Qingshankou Formation end period, and gas reservoir distributions were controlled by fault locations, activity periods, volcanic rock mass and porosities; the fault activity time is before 94.5 Ma indicated by simulation results. It is concluded that the integrated migration method is the best way for describing gas migration in the volcanic rocks. Slope zone, micro-structures in the sag, lithologic pinchout and volcanic mass are favorable zones for the volcanic gas exploration in the study area, meanwhile, the tight conglomerate or tight sand in the deep formation should also have a great potential for gas exploration.
2017, 42(3): 410-420.
doi: 10.3799/dqkx.2017.031
Abstract:
In the process of large carbonate platform formation and tectonic evolution of Tarim basin, the thick platform margin reef, intra-platform beach and deep dolomite carbonate sediments were developed, which formed the various types and large scale of karst fracture-cave systems by the reconstruction of multi period tectonic movement, and the system is an important field of oil and gas exploration and development inside the platform-basin transitional area marine carbonate. Based on the multidisciplinary static and dynamic comprehensive analysis of the field outcrop, underground geology, geophysical prediction, karst geological description, static characteristics and production dynamic data, this paper described the characteristics of reservoir space development, such as caves, dissolved pores and fractures as well as the formation mechanism of the large-scale karst fracture-cave system, and established the superimposed development model of unconformity exposed and fracture karst, and revealed the horizontal distribution of unconformity related karst and the longitudinal distribution and three-dimensional distribution of the fault karst. The comprehensive study shows that the composite karst fracture-cave system is the key to oil and gas accumulation, and is also the basis for the exploration and development of the complex oil and gas accumulation area. The establishment of the superimposed compound karst model is an effective way to guide the significant discovery and efficient development of the carbonate condensate gas field in Tazhong uplift area.
In the process of large carbonate platform formation and tectonic evolution of Tarim basin, the thick platform margin reef, intra-platform beach and deep dolomite carbonate sediments were developed, which formed the various types and large scale of karst fracture-cave systems by the reconstruction of multi period tectonic movement, and the system is an important field of oil and gas exploration and development inside the platform-basin transitional area marine carbonate. Based on the multidisciplinary static and dynamic comprehensive analysis of the field outcrop, underground geology, geophysical prediction, karst geological description, static characteristics and production dynamic data, this paper described the characteristics of reservoir space development, such as caves, dissolved pores and fractures as well as the formation mechanism of the large-scale karst fracture-cave system, and established the superimposed development model of unconformity exposed and fracture karst, and revealed the horizontal distribution of unconformity related karst and the longitudinal distribution and three-dimensional distribution of the fault karst. The comprehensive study shows that the composite karst fracture-cave system is the key to oil and gas accumulation, and is also the basis for the exploration and development of the complex oil and gas accumulation area. The establishment of the superimposed compound karst model is an effective way to guide the significant discovery and efficient development of the carbonate condensate gas field in Tazhong uplift area.
2017, 42(3): 421-434.
doi: 10.3799/dqkx.2017.032
Abstract:
Devonian-Carboniferous is the critical tectonic evolution period of the South Tianshan Ocean and the northern margin of Tarim Basin. Taking Upper Devonian to Lower Carboniferous outcrop of Bachu as the study area, this study further explores provenance, tectonic evolution and its geodynamic mechanism about the Tarim basin and the periphery orogen, based on depositional system, sandstone skeleton component, heavy minerals, especially detrial zircon geochronology analysis by LA-ICP-MS in situ U-Pb and Lu-Hf isotope.Sandstone skeleton component analysis shows that sandstone grains are dominated by mono crystalline quartz, and volcanic-metavolcanic fragments are rare.Its main provenance is the continental block provenance.The main proportions of heavy mineral assemblages are the stable heavy minerals, such as zircon, tourmaline, and TiO2 minerals. Heavy minerals analysis reflects the relatively distant source-sink systems and stable tectonic setting are possible. The geochronological samples show that the two samples have similar U-Pb age patterns and Hf isotopic compositions, mainly reflecting multiphase tectono-thermal events with age groups of 383-479 Ma, 710-932 Ma, 1 752-1 936 Ma, and 2 419-2 597 Ma respectively. Compared with the main potential source areas, the main provenance is the palaeohigh of Tarim basin. Meanwhile, the West Kunlunorogen and the Altunorogen may also have some contribution. However, there is no information about the northern orogenand island arcs. It shows the South Tianshan Ocean has not closed in this period, and there isn't subduction to the south in the northwestern margin of Tarim basin. In other words, the northwestern margin of Tarim basin is a passive continental margin during Late Devonian to Early Carboniferous.
Devonian-Carboniferous is the critical tectonic evolution period of the South Tianshan Ocean and the northern margin of Tarim Basin. Taking Upper Devonian to Lower Carboniferous outcrop of Bachu as the study area, this study further explores provenance, tectonic evolution and its geodynamic mechanism about the Tarim basin and the periphery orogen, based on depositional system, sandstone skeleton component, heavy minerals, especially detrial zircon geochronology analysis by LA-ICP-MS in situ U-Pb and Lu-Hf isotope.Sandstone skeleton component analysis shows that sandstone grains are dominated by mono crystalline quartz, and volcanic-metavolcanic fragments are rare.Its main provenance is the continental block provenance.The main proportions of heavy mineral assemblages are the stable heavy minerals, such as zircon, tourmaline, and TiO2 minerals. Heavy minerals analysis reflects the relatively distant source-sink systems and stable tectonic setting are possible. The geochronological samples show that the two samples have similar U-Pb age patterns and Hf isotopic compositions, mainly reflecting multiphase tectono-thermal events with age groups of 383-479 Ma, 710-932 Ma, 1 752-1 936 Ma, and 2 419-2 597 Ma respectively. Compared with the main potential source areas, the main provenance is the palaeohigh of Tarim basin. Meanwhile, the West Kunlunorogen and the Altunorogen may also have some contribution. However, there is no information about the northern orogenand island arcs. It shows the South Tianshan Ocean has not closed in this period, and there isn't subduction to the south in the northwestern margin of Tarim basin. In other words, the northwestern margin of Tarim basin is a passive continental margin during Late Devonian to Early Carboniferous.
2017, 42(3): 435-446.
doi: 10.3799/dqkx.2017.033
Abstract:
The Zaysan basin is located in northeastern Kazakhstan, one important country along "the Belt and Road". However, Permian petroleum accumulation research in Zaysan basin is relatively few. In this paper, Permian exploration potentials of the Zaysan basin are explored by a comparative study with adjacent northwestern margin of Junggar basin in tectonic and sedimentary evolution, hydrocarbon source rocks, reservoir cap assemblages, migration and accumulation patterns on the basis of background of tectonic evolution of the Zaysan basin. The results show both of them are the products of plate collisions and the sedimentary systems are all controlled by faults; similar to the Fengcheng Formation, the types of Maichat Formation source rocks are type Ⅰ and type Ⅱ; sources rocks deposited in high salinity, reducing environment and they are good source rocks; the reservoirs in the Zaysan basin are of medium porosity and low permeability reservoirs which indicates that the reservoir quality is relatively better. In Permian strata of the Zaysan basin there exists a large set of stratigraphic traps where the oil and gas can be directly accumulated so as to form oil and gas reservoirs. It is suggested that the oil and gas of the Permian strata in the Zaysan basin is characterized by huge potentials for exploration.
The Zaysan basin is located in northeastern Kazakhstan, one important country along "the Belt and Road". However, Permian petroleum accumulation research in Zaysan basin is relatively few. In this paper, Permian exploration potentials of the Zaysan basin are explored by a comparative study with adjacent northwestern margin of Junggar basin in tectonic and sedimentary evolution, hydrocarbon source rocks, reservoir cap assemblages, migration and accumulation patterns on the basis of background of tectonic evolution of the Zaysan basin. The results show both of them are the products of plate collisions and the sedimentary systems are all controlled by faults; similar to the Fengcheng Formation, the types of Maichat Formation source rocks are type Ⅰ and type Ⅱ; sources rocks deposited in high salinity, reducing environment and they are good source rocks; the reservoirs in the Zaysan basin are of medium porosity and low permeability reservoirs which indicates that the reservoir quality is relatively better. In Permian strata of the Zaysan basin there exists a large set of stratigraphic traps where the oil and gas can be directly accumulated so as to form oil and gas reservoirs. It is suggested that the oil and gas of the Permian strata in the Zaysan basin is characterized by huge potentials for exploration.
2017, 42(3): 447-452.
doi: 10.3799/dqkx.2017.034
Abstract:
The van Genuchten model is frequently used in expression of soil lithology and hydraulic feature of vadose zone. The included soil hydraulic parameters are sensitive factors in numerical simulation of rainfall recharge. It facilitates the understanding of the physical meaning of parameters, improving accuracy of numerical simulation of rainfall recharge and parameters regulation to analyze the sensitivity of each soil hydraulic parameter. In this study, one-dimensional variably saturated flow models were established by using HYDRUS software. Simulations were run under conditions of multiple sets of parameters which are set in the principle of changing one parameter and keeping the others invariant to evaluate parameter sensitivity of van Genuchten model by using actual recharge quantity, recharge process curve and maximum evaporation depth as the index. The case study chose multiple sets of measured parameters to evaluate the influence of parameter variation among different samples of the same lithology. The simulations results show that maximum evaporation depth is significantly affected by the n and α which are negatively related to it; θs, n, and Ks have a high sensibility to the variation of vertical groundwater recharge, however they will change with porosity, grain size distribution and bulk density of soil at the same time. It is concluded that the reasonable analysis of parameter sensitivity can only be done in combination of the study of their physical meaning.
The van Genuchten model is frequently used in expression of soil lithology and hydraulic feature of vadose zone. The included soil hydraulic parameters are sensitive factors in numerical simulation of rainfall recharge. It facilitates the understanding of the physical meaning of parameters, improving accuracy of numerical simulation of rainfall recharge and parameters regulation to analyze the sensitivity of each soil hydraulic parameter. In this study, one-dimensional variably saturated flow models were established by using HYDRUS software. Simulations were run under conditions of multiple sets of parameters which are set in the principle of changing one parameter and keeping the others invariant to evaluate parameter sensitivity of van Genuchten model by using actual recharge quantity, recharge process curve and maximum evaporation depth as the index. The case study chose multiple sets of measured parameters to evaluate the influence of parameter variation among different samples of the same lithology. The simulations results show that maximum evaporation depth is significantly affected by the n and α which are negatively related to it; θs, n, and Ks have a high sensibility to the variation of vertical groundwater recharge, however they will change with porosity, grain size distribution and bulk density of soil at the same time. It is concluded that the reasonable analysis of parameter sensitivity can only be done in combination of the study of their physical meaning.
2017, 42(3): 453-461.
doi: 10.3799/dqkx.2017.035
Abstract:
At present, the laboratory experiment of drilling fluid invasion problem mostly focus on small-scale, carrying out large-scale experiment based on physical parameters more similar with actual sediment would provide guidance for drilling fluid formulation during actual drilling process in hydrate-bearing formation and accurate well logging identification and hydrate reservoir evaluation. This experiment were based on artificial cores which were made according to the physical properties of hydrate-bearing formation in the Gulf of Mexico. Results indicate that the temperature and pressure rise when hydrate is heated to decompose, while the resistivity firstly increases and then decreasse, in which, hydrate equilibrium conditions are not only affected by temperature and pressure, but also by pore-water salinity. During drilling fluid invasion, the pressure spread rate is much faster than heat, hence it is probably that in-situ pore water and gas continue to form hydrate for pressure increase while temperature doesn't change. The high drilling fluid temperature is the main factor controlling hydrate decomposition, and pressure difference between drilling fluid and pore pressure can help improve the pore water pressure, which is beneficial to hydrate stability. Though high salinity drilling fluids are conducive to higher pressure difference and will inhibit hydrate formation in drilling fluid, it can also lead to gas hydrate dissociation. Therefore, in order to reduce the drilling risks in the hydrate-bearing formation, the density of drilling fluids should be increased during the safe density window range, but the density increase also increases the drilling fluid invasion. Therefore, a certain amount of kinetic inhibitors and fluid loss control agent leak loss control agents should be added in the low temperature drilling fluids. At the same time, the logging while drilling method or deep laterolog data should be chosen so as to avoid the distortion caused by drilling fluid invasion and hydrate decomposition.
At present, the laboratory experiment of drilling fluid invasion problem mostly focus on small-scale, carrying out large-scale experiment based on physical parameters more similar with actual sediment would provide guidance for drilling fluid formulation during actual drilling process in hydrate-bearing formation and accurate well logging identification and hydrate reservoir evaluation. This experiment were based on artificial cores which were made according to the physical properties of hydrate-bearing formation in the Gulf of Mexico. Results indicate that the temperature and pressure rise when hydrate is heated to decompose, while the resistivity firstly increases and then decreasse, in which, hydrate equilibrium conditions are not only affected by temperature and pressure, but also by pore-water salinity. During drilling fluid invasion, the pressure spread rate is much faster than heat, hence it is probably that in-situ pore water and gas continue to form hydrate for pressure increase while temperature doesn't change. The high drilling fluid temperature is the main factor controlling hydrate decomposition, and pressure difference between drilling fluid and pore pressure can help improve the pore water pressure, which is beneficial to hydrate stability. Though high salinity drilling fluids are conducive to higher pressure difference and will inhibit hydrate formation in drilling fluid, it can also lead to gas hydrate dissociation. Therefore, in order to reduce the drilling risks in the hydrate-bearing formation, the density of drilling fluids should be increased during the safe density window range, but the density increase also increases the drilling fluid invasion. Therefore, a certain amount of kinetic inhibitors and fluid loss control agent leak loss control agents should be added in the low temperature drilling fluids. At the same time, the logging while drilling method or deep laterolog data should be chosen so as to avoid the distortion caused by drilling fluid invasion and hydrate decomposition.
2017, 42(3): 462-470.
doi: 10.3799/dqkx.2017.036
Abstract:
Active fault detection is not only the foundation for the fault activity evaluation, but also the basis for prevention of natural earthquake disasters. The shallow seismic exploration is one of the effective methods for active fault detection. This study aims to further improve the fault activity evaluation with shallow seismic methods. We construct theoretical models of active fault of different fracture zone widths, apply the finite difference method of two-dimensional viscoelastic wave equation to simulate wave field response characteristics, use Hilbert transform method to extract the attributes of instantaneous frequency and instantaneous phase, and analyze the performance in the field of anti-noise and effect of practical applications of method. The results show: Combination of the vertical travel time section and seismic attributes can effectively obtain the response characteristics of active faults which cut through the Quaternary and achieve the evaluation of fault activity; However, when coherent noise reaches thirty percent, it is difficult to trace and identify the weak reflection signals in the Quaternary by the vertical travel time section and instantaneous frequency section, but instantaneous phase attributes can still effectively trace and identify the weak reflection signals with a high anti-noise ability. In the practical determination of active faults, both the vertical travel time section, instantaneous frequency section and instantaneous phase section can determine the existence of faults.The instantaneous phase attribute is the most obvious and prominent to show the characteristics of faults or fracture zones which cut through the Quaternary, whereas the vertical travel time section takes the second place.It is concluded that the instantaneous phase attribute is an important and effective seismic attribute to determine the fault activity.
Active fault detection is not only the foundation for the fault activity evaluation, but also the basis for prevention of natural earthquake disasters. The shallow seismic exploration is one of the effective methods for active fault detection. This study aims to further improve the fault activity evaluation with shallow seismic methods. We construct theoretical models of active fault of different fracture zone widths, apply the finite difference method of two-dimensional viscoelastic wave equation to simulate wave field response characteristics, use Hilbert transform method to extract the attributes of instantaneous frequency and instantaneous phase, and analyze the performance in the field of anti-noise and effect of practical applications of method. The results show: Combination of the vertical travel time section and seismic attributes can effectively obtain the response characteristics of active faults which cut through the Quaternary and achieve the evaluation of fault activity; However, when coherent noise reaches thirty percent, it is difficult to trace and identify the weak reflection signals in the Quaternary by the vertical travel time section and instantaneous frequency section, but instantaneous phase attributes can still effectively trace and identify the weak reflection signals with a high anti-noise ability. In the practical determination of active faults, both the vertical travel time section, instantaneous frequency section and instantaneous phase section can determine the existence of faults.The instantaneous phase attribute is the most obvious and prominent to show the characteristics of faults or fracture zones which cut through the Quaternary, whereas the vertical travel time section takes the second place.It is concluded that the instantaneous phase attribute is an important and effective seismic attribute to determine the fault activity.
2017, 42(3): 471-478.
doi: 10.3799/dqkx.2017.037
Abstract:
Syncretic processing of various types of gravimetric data is one of the challenging and hot issues in the modeling of Earth's gravitational field model (EGM). The general expressions of the spectral weight and spectral combination of the united-processing of various types of gravimetric data are presented in this paper. What's more, the detailed expressions of spectral combination formulae and the corresponding spectral weights in the EGM determination using satellite-to-satellite tracking (SST) data and satellite gravity gradient (SGG) data of GOCE satellite are derived, based on spherical harmonic analysis method. Experimentation results show that the EGM computed by SGG data is improved by SST data in the low order, whatever the data are simulated or surveyed. It is concluded that as many types of gravimetric data as possible should be combined together in the data processing in order to improve the quality and reliability with widening scope and to improve the precision and spatial resolution of the computational results.
Syncretic processing of various types of gravimetric data is one of the challenging and hot issues in the modeling of Earth's gravitational field model (EGM). The general expressions of the spectral weight and spectral combination of the united-processing of various types of gravimetric data are presented in this paper. What's more, the detailed expressions of spectral combination formulae and the corresponding spectral weights in the EGM determination using satellite-to-satellite tracking (SST) data and satellite gravity gradient (SGG) data of GOCE satellite are derived, based on spherical harmonic analysis method. Experimentation results show that the EGM computed by SGG data is improved by SST data in the low order, whatever the data are simulated or surveyed. It is concluded that as many types of gravimetric data as possible should be combined together in the data processing in order to improve the quality and reliability with widening scope and to improve the precision and spatial resolution of the computational results.
2017, 42(3): 479-484.
doi: 10.3799/dqkx.2017.038
Abstract:
Space-based GPS detection can provide the global distribution, high accuracy, high vertical resolution of the ionosphere observation data, compensate for the problem of regional restriction and low vertical resolution in ground-based GPS detection. To enrich the relevant research, this study analyses the spatial distribution variation of electron density based on COSMIC occultation data from 2008—2011 by statistical method. Results show that electron density is dominated by the EIA and WSA. With the solar activity enhancement, EIA extends into the middle latitudes from 250 km to 350 km height range, and WSA occurs not only in summer of the southern hemisphere, but also in spring and autumn there while electron density values during night time are greater than those during daytime from 300 km to 500 km height range; The electron density has obvious WSA phenomenon from 250 km to 500 km height range. And with the solar activity enhancement, the geographic range of abnormal regional expands.
Space-based GPS detection can provide the global distribution, high accuracy, high vertical resolution of the ionosphere observation data, compensate for the problem of regional restriction and low vertical resolution in ground-based GPS detection. To enrich the relevant research, this study analyses the spatial distribution variation of electron density based on COSMIC occultation data from 2008—2011 by statistical method. Results show that electron density is dominated by the EIA and WSA. With the solar activity enhancement, EIA extends into the middle latitudes from 250 km to 350 km height range, and WSA occurs not only in summer of the southern hemisphere, but also in spring and autumn there while electron density values during night time are greater than those during daytime from 300 km to 500 km height range; The electron density has obvious WSA phenomenon from 250 km to 500 km height range. And with the solar activity enhancement, the geographic range of abnormal regional expands.
