The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts ...The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts due to its scale, high grade and abundant associated ores. Because of the insufficient reliable dating of intrusive rocks, the relationship between mineralization and the magmatic activities is still unknown. In order to study this key scientific issue and the ore-forming processes of the Zoige uranium ore field, the LA-ICP-MS zircon U-Pb dating of magmatic rocks was obtained:64.08±0.59 Ma for the granite-prophyry and ~200 Ma for the dolerite. U-Pb dating results of uraninite from the Zoige uranium ore field are mainly concentrated on ~90 Ma and ~60 Ma. According to LA-ICP-MS U-Pb zircon dating, the ages for the dolerite, porphyry granite and granodiorite are 200 Ma, 64.08 Ma approximately and 226.5-200.88 Ma, respectively. This indicates that the mineralization has close relationship with activities of the intermediate-acidic magma. The ages of the granite porphyry are consistent with those uraninite U-Pb dating results achieved by previous studies, which reflects the magmatic and ore-forming event during the later Yanshanian. Based on the data from previous researches, the ore bodies in the Zoige uranium ore field can be divided into two categories:the single uranium type and the uranium with polymetal mineralization type. The former formed at late Cretaceous(about 90 Ma), while the latter, closely related to the granite porphyry, formed at early Paleogene(about 60 Ma). And apart from ore forming elemental uranium, the latter is often associated with polymetallic elements, such as molybdenum, nickel, zinc, etc.展开更多
Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distin...Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distinct rock types.Generally,these methods are applied to petrophysical data that are measured at a pressure other than reservoir pressure.Since the pressure changes the pore structure of rock,the effect of overburden pressure on rock typing should be considered.In this study,porosity and permeability of 113 core samples were measured at five different pressures.To investigate the effect of pressure on determination of rock types,FZI,FZI~*and Winland methods were applied.Results indicated that although most of the samples remain in the same rock type when pressure changes,some of them show different trends.These are related to the mineralogy and changes in pore system of the samples due to pressure change.Additionally,the number of rock types increases with increasing pressure.Furthermore,the effect of overburden pressure on determination of rock types is more clearly observed in the Winland and FZI~*methods.Also,results revealed that a more precise reservoir dynamic simulation can be obtained by considering the reservoir rock typing process at reservoir conditions.展开更多
Dariyan (Shuaiba) Formation is one of the main reservoir units in the Persian Gulf and South Western Iran. The microfacies and depositional environment of this formation is been investigated in the current study and i...Dariyan (Shuaiba) Formation is one of the main reservoir units in the Persian Gulf and South Western Iran. The microfacies and depositional environment of this formation is been investigated in the current study and influencing factors in reservoir characteristics have been discussed for Dariyan reservoir in the Soroush oil field. Facies analysis conducted on core and cutting samples indicated that Dariyan Formation is mainly deposited on a carbonate ramp setting with a shallow intra shelf basin. In addition, it has been demonstrated that facies changes reflect the main controls of the tectonic and climate (sea level fluctuations) during the deposition of these sediments. To determine the reservoir unites in this formation, 5 electrofacies were determined by neural network method that it is using different petrophysical logs (i.e. GR, PHIE and SWE). Using rock typing as the best way to establish an association between the various collected data (e.g. logs and cores) and geological descriptions 4 hydraulic flow units or rock types, determined on the basis of the Flow Zone Indicator (FZI) method in the Dariyan Formation of the Soroush field. Establishing a correlation between microfacies and rock types, the carbonate zones with moderate to good reservoir properties and also the intervals with the highest reservoir quality were determined.展开更多
We used the geological map and published rock density measurements to compile the digital rock density model for the Hong Kong territories.We then estimated the average density for the whole territory.According to our...We used the geological map and published rock density measurements to compile the digital rock density model for the Hong Kong territories.We then estimated the average density for the whole territory.According to our result,the rock density values in Hong Kong vary from 2101 to 2681 kg·m^(-3).These density values are typically smaller than the average density of 2670 kg·m^(-3),often adopted to represent the average density of the upper continental crust in physical geodesy and gravimetric geophysics applications.This finding reflects that the geological configuration in Hong Kong is mainly formed by light volcanic formations and lava flows with overlying sedimentary deposits at many locations,while the percentage of heavier metamorphic rocks is very low(less than 1%).This product will improve the accuracy of a detailed geoid model and orthometric heights.展开更多
The Oligo-Miocene Asmari Formation is one of the most important hydrocarbon reservoirs in the Middle East.The oilfield under study is one of the largest oilfields in the Zagros basin with the Asmari Formation being th...The Oligo-Miocene Asmari Formation is one of the most important hydrocarbon reservoirs in the Middle East.The oilfield under study is one of the largest oilfields in the Zagros basin with the Asmari Formation being the major reservoir rock.In this study,petrographic analyses,petrophysical data and neural network clustering techniques were used for identifying rock types in the Asmari reservoir.Facies analysis of the Asmari Formation in the study area has resulted in the definition of 1 clastic lithofacies and 14 carbonate microfacies types.Using petrophysical logs from 43 wells and their correlation with capillary pressure(Pc)curves,led to the recognition of 7 electrofacies(EF1-EF7).Microscopic evidence of Electrofacies group C1 and S1 show that the sedimentary facies of these electrofacies are most commonly found in restricted and shoal facies belts zone.Also,petrographic studies show that the sedimentary facies of C2,C3,C4,S2 and S3 were formed in the open marine,Lagoon,and Tidal flat facies belt zone of homoclinal ramp sedimentary environment during the Oligo-Miocene based on relative sea level changes respectively.The link between electrofacies and geological data indicated that both sedimentary and diagenetic processes controlled the reservoir quality of the Asmari Formation.Porosity,permeability and water saturation were used to estimate the reservoir quality of each electrofacies.EFs 1 and 2 with high porosity and permeability,low water saturation is considered as the best reservoir with regard to sedimentary textures(dolowackestone and dolograinstone)and the effect of diagenetic processes such as dolomitization processes.Vuggy,growth framework and interparticle porosities are major in EF-2,while the intercrystalline porosity is the major type in EF-1.EFs 3 and 4 show low values of porosity,permeability and high percentage of water saturations,which characterizes them as poor reservoir rocks.Finally,EF-5 is the only electrofacies in the siliciclastic parts of the Asmari reservoir,which is composed of rounded and well-sorted quartz grains that are slightly cemented.In sandstone electrofacies,electrofacies EF-5(S1),is the best type of sandstone reservoir rock and to move towards electrofacies EF-7(S3),will reduce reservoir quality.In carbonate electrofacies,also,electrofacies no 1,the best type of carbonate reservoir rock can be observed and move towards electrofacie number 4,lower quality of reservoir rocks is seen.展开更多
Due to the complicated lithology in the ES3 Member of the Shahejie Formation in the Shulu sag,Jizhong depression,it is difficult to classify the rock types and characterize the reservoirs at the marl intervals.In this...Due to the complicated lithology in the ES3 Member of the Shahejie Formation in the Shulu sag,Jizhong depression,it is difficult to classify the rock types and characterize the reservoirs at the marl intervals.In this paper,a four-element classification method has been proposed,and seven rock types have been identified by analyzing the mineral composition.The primary rock types are medium-high organic carbonate rocks and medium-high organic shaly-siliceous carbonate rocks.With the methods of field emission scanning electron microscopy,high-pressure mercury intrusion,nitrogen adsorption,and nano-CT,four types of reservoir spaces have been identified,including intra-granular pores,intergranular pores(inter-crystalline pores),organic pores,and micro-fractures.By combining the method of high-pressure mercury intrusion with the method of the nitrogen adsorption,the porosity of the marl has been measured,ranging from 0.73%to 5.39%.The distribution of the pore sizes is bimodal,and the pore types are dominated by micron pores.Through this study,it has been concluded that the sag area to the east of Well ST1H is the favorable area for the development of self-sourced and self-reservoired shale oil.According to the results of geochemical and reservoir analysis,the III Oil Group may have sweet spot layers.展开更多
Pendulum-type ( μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse w...Pendulum-type ( μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently. The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fourier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendulum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of 2~(1/2), most of those frequencies satisfied the quantitative expression (2~(1/2))i V p/2△ .展开更多
The Jinjiazhuang gold deposit occurs in the Zhangjiakou gold field, Northwest Hebei. The ore bodies are mostly hosted in Xiaozhangjiakou ultrabasic rocks dominated by diopsidite. Electron microprobe analyses indicate ...The Jinjiazhuang gold deposit occurs in the Zhangjiakou gold field, Northwest Hebei. The ore bodies are mostly hosted in Xiaozhangjiakou ultrabasic rocks dominated by diopsidite. Electron microprobe analyses indicate that the deposit is characterized by the enrichment of some platinum group elements in principal metallic minerals such as chalcopyrite, galena, sphalerite and pyrite, and the presence of millerite. Stable isotope studies show that carbon, sulfur and most of the metallogenic elements were probably derived largely from the host Xiaozhangjiakou ultrabasic rocks and that it is possible that the ore\|forming fluid was predominated by meteoric water.展开更多
Metallogenic models of gold deposits of quartz vein type and altered rock type will be dis-cussed in this note. They are considered to be closely related to granite spatially andgenetically.
The discovery of the Bozhong 19-6 gas field,the largest integrated condensate gas field in the eastern China in 2018,opened up a new field for the natural gas exploration deep strata in the Bohai Bay Basin,demonstrati...The discovery of the Bozhong 19-6 gas field,the largest integrated condensate gas field in the eastern China in 2018,opened up a new field for the natural gas exploration deep strata in the Bohai Bay Basin,demonstrating there is a great potential for natural gas exploration in oil-type basins.The ethane isotope of the Bozhong 19-6 condensate gas is heavy,showing the characteristics of partial humic gas.In this paper,aimed at the source rocks of the Bozhong 19-6 gas field in the Bohai Bay Basin,the characteristics of the source rocks in the Bozhong 19-6 structural belt were clarified and the reason are explained from impact of microorganism degradation on hydrocarbon generation of source rocks why the condensate oil and gas had heavy carbon isotope and why it showed partial humic characteristics was explored based on the research of parent materials.The following conclusions were obtained:The paleontology of the Bozhong 19-6 structural belt and its surrounding sub-sags is dominated by higher plants,such as angiosperm and gymnosperm.During the formation of source rocks,under the intensive transformation of microorganism,the original sedimentary organic matter such as higher plants was degraded and transformed by defunctionalization.Especially,the transformation of anaerobic microorganisms on source rocks causes the degradation and defunctionalization of a large number of humic products such as higher plants and the increase of hydrogen content.The degradation and transformation of microorganism don't transform the terrestrial humic organic matter into newly formed“sapropel”hydrocarbons,the source rocks are mixed partial humic source rocks.As a result,hydrogen content incrased and the quality of source rocks was improved,forming the partial humic source rocks dominated by humic amorphous bodies.The partial humic source rocks are the main source rocks in the Bozhong 19-6 gas field,and it is also the internal reason why the isotope of natural gas is heavy.展开更多
The ever-increasing demand for oil and gas has driven its exploration in rather extreme conditions. In Lamu offshore, which is hitherto underexplored, most of the wells already drilled turned out dry save for a few we...The ever-increasing demand for oil and gas has driven its exploration in rather extreme conditions. In Lamu offshore, which is hitherto underexplored, most of the wells already drilled turned out dry save for a few wells with hydrocarbon shows despite the promising reservoir properties and related geological structures. This, therefore, necessitated a source rock evaluation study in the area to ascertain the presence and potential of the source rock by integrating the geochemical data analysis and petroleum system modeling. The shallow Lamu offshore source rock quantity, quality, and maturity have been estimated through the determination of the total organic carbon (TOC) average values, Kerogen typing, and Rock-Eval pyrolysis measurements respectively. Geochemical data for Kubwa-1, Mbawa-1, Pomboo-1, and Simba-1 were evaluated for determining the source rock potential for hydrocarbon generation. Petroleum system modeling was applied in evaluating geological conditions necessary for a successful charge within a software that integrated geochemical and petrophysical characterization of the sedimentary formations in conjunction with boundary conditions that include basal heat flow, sediment-water interface temperature, and Paleo-water depth. The average TOC of 0.89 wt % in the study area suggests a fair organic richness which seems higher in the late cretaceous (0.98 wt %) than in the Paleocene (0.81 wt %). Vitrinite reflectance and T<sub>max</sub> values in the study area indicate the possible presence of both mature and immature source rocks. Type III Kerogen was the most dominant Kerogen type, and gas shows are the most frequent hydrocarbon encountered in the Lamu Basin with a few cases registering type II/III and type II. The charge properties (i.e. Temperature, transformation ratio, and Vitrinite reflectance) over geologic time at each of the wells have been estimated and their spatial variation mapped as seen from the burial history and depth curves overlaid with temperature, transformation ratio, and Vitrinite reflectance respectively. From the upper cretaceous maturity maps, the results seem to favor near coastal regions where average TOC is about 1.4 wt %, Vitrinite reflectance is more than 0.5%, transformation ratio is more than 10%, and temperatures range from 80°C to 160°C. The results postulate the absence of a definitive effective source rock with a likelihood of having cases of potential and possible source rocks. Moreover, greater uncertainty rests on the source rock’s presence and viability tending toward the deep offshore. Geochemical analysis and petroleum system modeling for hydrocarbon source rock evaluation improved the understanding of the occurrence of the possible and potential source rocks and processes necessary for hydrocarbon generation.展开更多
基金supported financially by the National Natural Scientific Foundation of China (Grants No. 40872069 and 41173059)the National Basic Research Program of China (973 Program) (Grants No. 2015CB453000)+1 种基金China Geological Survey (Grants No. 12120113095500)the Foundation of China Nuclear Geology (Grants No. 201148)
文摘The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts due to its scale, high grade and abundant associated ores. Because of the insufficient reliable dating of intrusive rocks, the relationship between mineralization and the magmatic activities is still unknown. In order to study this key scientific issue and the ore-forming processes of the Zoige uranium ore field, the LA-ICP-MS zircon U-Pb dating of magmatic rocks was obtained:64.08±0.59 Ma for the granite-prophyry and ~200 Ma for the dolerite. U-Pb dating results of uraninite from the Zoige uranium ore field are mainly concentrated on ~90 Ma and ~60 Ma. According to LA-ICP-MS U-Pb zircon dating, the ages for the dolerite, porphyry granite and granodiorite are 200 Ma, 64.08 Ma approximately and 226.5-200.88 Ma, respectively. This indicates that the mineralization has close relationship with activities of the intermediate-acidic magma. The ages of the granite porphyry are consistent with those uraninite U-Pb dating results achieved by previous studies, which reflects the magmatic and ore-forming event during the later Yanshanian. Based on the data from previous researches, the ore bodies in the Zoige uranium ore field can be divided into two categories:the single uranium type and the uranium with polymetal mineralization type. The former formed at late Cretaceous(about 90 Ma), while the latter, closely related to the granite porphyry, formed at early Paleogene(about 60 Ma). And apart from ore forming elemental uranium, the latter is often associated with polymetallic elements, such as molybdenum, nickel, zinc, etc.
文摘Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distinct rock types.Generally,these methods are applied to petrophysical data that are measured at a pressure other than reservoir pressure.Since the pressure changes the pore structure of rock,the effect of overburden pressure on rock typing should be considered.In this study,porosity and permeability of 113 core samples were measured at five different pressures.To investigate the effect of pressure on determination of rock types,FZI,FZI~*and Winland methods were applied.Results indicated that although most of the samples remain in the same rock type when pressure changes,some of them show different trends.These are related to the mineralogy and changes in pore system of the samples due to pressure change.Additionally,the number of rock types increases with increasing pressure.Furthermore,the effect of overburden pressure on determination of rock types is more clearly observed in the Winland and FZI~*methods.Also,results revealed that a more precise reservoir dynamic simulation can be obtained by considering the reservoir rock typing process at reservoir conditions.
文摘Dariyan (Shuaiba) Formation is one of the main reservoir units in the Persian Gulf and South Western Iran. The microfacies and depositional environment of this formation is been investigated in the current study and influencing factors in reservoir characteristics have been discussed for Dariyan reservoir in the Soroush oil field. Facies analysis conducted on core and cutting samples indicated that Dariyan Formation is mainly deposited on a carbonate ramp setting with a shallow intra shelf basin. In addition, it has been demonstrated that facies changes reflect the main controls of the tectonic and climate (sea level fluctuations) during the deposition of these sediments. To determine the reservoir unites in this formation, 5 electrofacies were determined by neural network method that it is using different petrophysical logs (i.e. GR, PHIE and SWE). Using rock typing as the best way to establish an association between the various collected data (e.g. logs and cores) and geological descriptions 4 hydraulic flow units or rock types, determined on the basis of the Flow Zone Indicator (FZI) method in the Dariyan Formation of the Soroush field. Establishing a correlation between microfacies and rock types, the carbonate zones with moderate to good reservoir properties and also the intervals with the highest reservoir quality were determined.
基金supported by the Hong Kong GRF RGC project 15217222:“Modernization of the leveling network in the Hong Kong territories.”。
文摘We used the geological map and published rock density measurements to compile the digital rock density model for the Hong Kong territories.We then estimated the average density for the whole territory.According to our result,the rock density values in Hong Kong vary from 2101 to 2681 kg·m^(-3).These density values are typically smaller than the average density of 2670 kg·m^(-3),often adopted to represent the average density of the upper continental crust in physical geodesy and gravimetric geophysics applications.This finding reflects that the geological configuration in Hong Kong is mainly formed by light volcanic formations and lava flows with overlying sedimentary deposits at many locations,while the percentage of heavier metamorphic rocks is very low(less than 1%).This product will improve the accuracy of a detailed geoid model and orthometric heights.
文摘The Oligo-Miocene Asmari Formation is one of the most important hydrocarbon reservoirs in the Middle East.The oilfield under study is one of the largest oilfields in the Zagros basin with the Asmari Formation being the major reservoir rock.In this study,petrographic analyses,petrophysical data and neural network clustering techniques were used for identifying rock types in the Asmari reservoir.Facies analysis of the Asmari Formation in the study area has resulted in the definition of 1 clastic lithofacies and 14 carbonate microfacies types.Using petrophysical logs from 43 wells and their correlation with capillary pressure(Pc)curves,led to the recognition of 7 electrofacies(EF1-EF7).Microscopic evidence of Electrofacies group C1 and S1 show that the sedimentary facies of these electrofacies are most commonly found in restricted and shoal facies belts zone.Also,petrographic studies show that the sedimentary facies of C2,C3,C4,S2 and S3 were formed in the open marine,Lagoon,and Tidal flat facies belt zone of homoclinal ramp sedimentary environment during the Oligo-Miocene based on relative sea level changes respectively.The link between electrofacies and geological data indicated that both sedimentary and diagenetic processes controlled the reservoir quality of the Asmari Formation.Porosity,permeability and water saturation were used to estimate the reservoir quality of each electrofacies.EFs 1 and 2 with high porosity and permeability,low water saturation is considered as the best reservoir with regard to sedimentary textures(dolowackestone and dolograinstone)and the effect of diagenetic processes such as dolomitization processes.Vuggy,growth framework and interparticle porosities are major in EF-2,while the intercrystalline porosity is the major type in EF-1.EFs 3 and 4 show low values of porosity,permeability and high percentage of water saturations,which characterizes them as poor reservoir rocks.Finally,EF-5 is the only electrofacies in the siliciclastic parts of the Asmari reservoir,which is composed of rounded and well-sorted quartz grains that are slightly cemented.In sandstone electrofacies,electrofacies EF-5(S1),is the best type of sandstone reservoir rock and to move towards electrofacies EF-7(S3),will reduce reservoir quality.In carbonate electrofacies,also,electrofacies no 1,the best type of carbonate reservoir rock can be observed and move towards electrofacie number 4,lower quality of reservoir rocks is seen.
基金supported by the National Basic Research Program of China(973 Program)(No.2014CB239001).
文摘Due to the complicated lithology in the ES3 Member of the Shahejie Formation in the Shulu sag,Jizhong depression,it is difficult to classify the rock types and characterize the reservoirs at the marl intervals.In this paper,a four-element classification method has been proposed,and seven rock types have been identified by analyzing the mineral composition.The primary rock types are medium-high organic carbonate rocks and medium-high organic shaly-siliceous carbonate rocks.With the methods of field emission scanning electron microscopy,high-pressure mercury intrusion,nitrogen adsorption,and nano-CT,four types of reservoir spaces have been identified,including intra-granular pores,intergranular pores(inter-crystalline pores),organic pores,and micro-fractures.By combining the method of high-pressure mercury intrusion with the method of the nitrogen adsorption,the porosity of the marl has been measured,ranging from 0.73%to 5.39%.The distribution of the pore sizes is bimodal,and the pore types are dominated by micron pores.Through this study,it has been concluded that the sag area to the east of Well ST1H is the favorable area for the development of self-sourced and self-reservoired shale oil.According to the results of geochemical and reservoir analysis,the III Oil Group may have sweet spot layers.
基金Projects 50525825 and 90815010 supported by the National Natural Science Foundation of China2009CB724608 by the National Basic Research Program of ChinaBK2008002 by the Natural Science Foundation of Jiangsu Province
文摘Pendulum-type ( μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently. The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fourier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendulum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of 2~(1/2), most of those frequencies satisfied the quantitative expression (2~(1/2))i V p/2△ .
文摘The Jinjiazhuang gold deposit occurs in the Zhangjiakou gold field, Northwest Hebei. The ore bodies are mostly hosted in Xiaozhangjiakou ultrabasic rocks dominated by diopsidite. Electron microprobe analyses indicate that the deposit is characterized by the enrichment of some platinum group elements in principal metallic minerals such as chalcopyrite, galena, sphalerite and pyrite, and the presence of millerite. Stable isotope studies show that carbon, sulfur and most of the metallogenic elements were probably derived largely from the host Xiaozhangjiakou ultrabasic rocks and that it is possible that the ore\|forming fluid was predominated by meteoric water.
基金Project supported by Doctorate Foundation of the State Education Commission of China.
文摘Metallogenic models of gold deposits of quartz vein type and altered rock type will be dis-cussed in this note. They are considered to be closely related to granite spatially andgenetically.
文摘The discovery of the Bozhong 19-6 gas field,the largest integrated condensate gas field in the eastern China in 2018,opened up a new field for the natural gas exploration deep strata in the Bohai Bay Basin,demonstrating there is a great potential for natural gas exploration in oil-type basins.The ethane isotope of the Bozhong 19-6 condensate gas is heavy,showing the characteristics of partial humic gas.In this paper,aimed at the source rocks of the Bozhong 19-6 gas field in the Bohai Bay Basin,the characteristics of the source rocks in the Bozhong 19-6 structural belt were clarified and the reason are explained from impact of microorganism degradation on hydrocarbon generation of source rocks why the condensate oil and gas had heavy carbon isotope and why it showed partial humic characteristics was explored based on the research of parent materials.The following conclusions were obtained:The paleontology of the Bozhong 19-6 structural belt and its surrounding sub-sags is dominated by higher plants,such as angiosperm and gymnosperm.During the formation of source rocks,under the intensive transformation of microorganism,the original sedimentary organic matter such as higher plants was degraded and transformed by defunctionalization.Especially,the transformation of anaerobic microorganisms on source rocks causes the degradation and defunctionalization of a large number of humic products such as higher plants and the increase of hydrogen content.The degradation and transformation of microorganism don't transform the terrestrial humic organic matter into newly formed“sapropel”hydrocarbons,the source rocks are mixed partial humic source rocks.As a result,hydrogen content incrased and the quality of source rocks was improved,forming the partial humic source rocks dominated by humic amorphous bodies.The partial humic source rocks are the main source rocks in the Bozhong 19-6 gas field,and it is also the internal reason why the isotope of natural gas is heavy.
文摘The ever-increasing demand for oil and gas has driven its exploration in rather extreme conditions. In Lamu offshore, which is hitherto underexplored, most of the wells already drilled turned out dry save for a few wells with hydrocarbon shows despite the promising reservoir properties and related geological structures. This, therefore, necessitated a source rock evaluation study in the area to ascertain the presence and potential of the source rock by integrating the geochemical data analysis and petroleum system modeling. The shallow Lamu offshore source rock quantity, quality, and maturity have been estimated through the determination of the total organic carbon (TOC) average values, Kerogen typing, and Rock-Eval pyrolysis measurements respectively. Geochemical data for Kubwa-1, Mbawa-1, Pomboo-1, and Simba-1 were evaluated for determining the source rock potential for hydrocarbon generation. Petroleum system modeling was applied in evaluating geological conditions necessary for a successful charge within a software that integrated geochemical and petrophysical characterization of the sedimentary formations in conjunction with boundary conditions that include basal heat flow, sediment-water interface temperature, and Paleo-water depth. The average TOC of 0.89 wt % in the study area suggests a fair organic richness which seems higher in the late cretaceous (0.98 wt %) than in the Paleocene (0.81 wt %). Vitrinite reflectance and T<sub>max</sub> values in the study area indicate the possible presence of both mature and immature source rocks. Type III Kerogen was the most dominant Kerogen type, and gas shows are the most frequent hydrocarbon encountered in the Lamu Basin with a few cases registering type II/III and type II. The charge properties (i.e. Temperature, transformation ratio, and Vitrinite reflectance) over geologic time at each of the wells have been estimated and their spatial variation mapped as seen from the burial history and depth curves overlaid with temperature, transformation ratio, and Vitrinite reflectance respectively. From the upper cretaceous maturity maps, the results seem to favor near coastal regions where average TOC is about 1.4 wt %, Vitrinite reflectance is more than 0.5%, transformation ratio is more than 10%, and temperatures range from 80°C to 160°C. The results postulate the absence of a definitive effective source rock with a likelihood of having cases of potential and possible source rocks. Moreover, greater uncertainty rests on the source rock’s presence and viability tending toward the deep offshore. Geochemical analysis and petroleum system modeling for hydrocarbon source rock evaluation improved the understanding of the occurrence of the possible and potential source rocks and processes necessary for hydrocarbon generation.