This study examined the geochemical features of pore water in the diapiric area of the Yinggehai Basin, northwestern South China Sea, and illuminated the origin and evolution of basin fluids. Pore water with low salin...This study examined the geochemical features of pore water in the diapiric area of the Yinggehai Basin, northwestern South China Sea, and illuminated the origin and evolution of basin fluids. Pore water with low salinity occurs in marine sediments in the diapiric area even without meteoric water infiltration. The presence of low-salinity water within deep, overpressured compartments is assumed to be due to smectite-illite transformation. Howerver, in shallow portions（less than 2 000 m） of diapiric areas with normal pressure, pore water has a much wider variation and much lower salinity than that in the overpressured intervals. Its total dissolved solid（TDS） content is ~5 336 to 35 939 mg/L. Moreover, smectite and chlorite content sharply decreases as kaolinite and illite content increase in shallower intervals. The geochemical variation of pore water in diapiric structures indicates the expulsion of low-salinity, overpressured fluids along vertical faults. Strong injection of hot fluids from deep overpressured sediments results in rapid clay mineral transformation in shallow reservoirs. Consequently, fluid mixing due to fluid expulsion from deeper overpressured deposits leads to variation in salinity and ionic composition as well as some diagenetic reactions. This includes transformation of clay minerals caused by the higher temperatur of deeper hot fluids, e.g., the transfromation of smectite to illite and chlorite to kaolinite. Therefore, variations in salinity and ionic compositions in various pressured systems provide a clue to flow pathways and associated diagenetic reactions.展开更多
Oil and gas currently still hold a leading role in the global energy mix.The recent drastic increase in unconventional oil and gas production contributes significantly to strike a balance between the global demand and...Oil and gas currently still hold a leading role in the global energy mix.The recent drastic increase in unconventional oil and gas production contributes significantly to strike a balance between the global demand and supply of oil and gas.However,a range of important fundamental questions about the unconventional oil and gas resources have not been adequately answered.Little is known about the distribution and accumulation patterns,as well as the exploration and development characteristics of unconventional oil and gas.The current status of global oil and gas exploration was reviewed and four key theoretical issues regarding the unconventional oil and gas geology were identified:(1)the traditional concept and definition of“petroleum system”needs to be revisited.The concept of a“holistic-process accumulation”model of a“total petroleum system”in petroliferous basins was proposed to analyze the unconventional hydrocarbon accumulation mechanisms from four key aspects of quantitative studies on hydrocarbon generation-expulsion-migration-accumulation processes.(2)The second issue is related to fine-grained sedimentary system and sedimentary facies of tight reservoirs.Through analyzing the relationship between fine-grained sediments and unconventional hydrocarbon accumulation,three research integration areas were put forward.(3)The third issue is on the micro-nano pore system and fluid phase behavior in shales and tight reservoirs.Five aspects of micro-nano pore system were identified to focus on unconventional hydrocarbon research,and the characteristics of micro-nano pore development and fluid phase behavior in micro-nanopores were elucidated.(4)The fourth issue is related to unconventional hydrocarbon accumulation patterns and resource evaluation.Based on the characteristics of unconventional hydrocarbon accumulation,an evaluation system for unconventional hydrocarbon resources was established and optimized.展开更多
During the past two years the shale gas exploration in Southern Sichuan basin received some exciting achievements.Data of a new appraisal well showed that the gas producrtions of vertical well and horizontal well are^...During the past two years the shale gas exploration in Southern Sichuan basin received some exciting achievements.Data of a new appraisal well showed that the gas producrtions of vertical well and horizontal well are^1.5×104 m3/day/well(with maximum^3.5×104 m3/day/well)and^12.5×104 m3/day/well(with maximum^40×104 m3/day/well),respectively,indicating a good gas potential in this area.Eight core samples from the reservoir were investigated by using a carbon sulfur analyzer,microphotometry,x-ray diffractometry,field-emission scanning electron microscopy(FE-SEM),mercury injection porosimetry(MIP),and low-pressure nitrogen adsorption to obtain a better understanding of the reservoir characteristics of the Upper OrdovicianeLower Silurian organic-rich shale.Results show that the total organic carbon(TOC)content ranges from 0.5%to 5.9%,whereas the equivalent vitrinite reflectance(VRr)is between 2.8%and 3.0%.Pores in the studied samples were observed in three modes of occurrence,namely,interparticle pores,intraparticle pores,and intraparticle organic pores.The total porosity(P)ranges from 1.6%to 5.3%,and MIP data sets suggest that pores with throats larger than 20 nm contribute little to the pore volume.Low-pressure N2 adsorption isotherms indicate that the total specific surface area(SBET)ranges from 9.6 m2/g to 18.9 m2/g,and the pore volume(V)ranges from 0.011 cm3/g to 0.020 cm3/g.The plot of dV/dW versus W shows that the fine mesopores(pore size(BJH)<4 nm)mainly contribute to the pore volume.The P,SBET,and V show a good positive correlation with TOC and a weak positive correlation with the total clay mineral content,thus indicating that the nanopores are mainly generated by the decomposition of organic matter.The reservoir characteristics of the Upper OrdovicianeLower Silurian organic-rich shale are comparable with commercial shale gas plays in North America.The sample gas contents with TOC>2%are more than 3.0 m3/ton.The observation can be a good reference for the future exploration and evaluation of reservoir in t展开更多
基金the projects the National Natural Science Foundation of China (Nos. 91028009, 41476032 and 40806019)the Special Foundation for State Major Basic Research Program of China (No. 2011ZX05025-0020-020-03)
文摘This study examined the geochemical features of pore water in the diapiric area of the Yinggehai Basin, northwestern South China Sea, and illuminated the origin and evolution of basin fluids. Pore water with low salinity occurs in marine sediments in the diapiric area even without meteoric water infiltration. The presence of low-salinity water within deep, overpressured compartments is assumed to be due to smectite-illite transformation. Howerver, in shallow portions（less than 2 000 m） of diapiric areas with normal pressure, pore water has a much wider variation and much lower salinity than that in the overpressured intervals. Its total dissolved solid（TDS） content is ~5 336 to 35 939 mg/L. Moreover, smectite and chlorite content sharply decreases as kaolinite and illite content increase in shallower intervals. The geochemical variation of pore water in diapiric structures indicates the expulsion of low-salinity, overpressured fluids along vertical faults. Strong injection of hot fluids from deep overpressured sediments results in rapid clay mineral transformation in shallow reservoirs. Consequently, fluid mixing due to fluid expulsion from deeper overpressured deposits leads to variation in salinity and ionic composition as well as some diagenetic reactions. This includes transformation of clay minerals caused by the higher temperatur of deeper hot fluids, e.g., the transfromation of smectite to illite and chlorite to kaolinite. Therefore, variations in salinity and ionic compositions in various pressured systems provide a clue to flow pathways and associated diagenetic reactions.
基金This work was funded by National Science and Technology Major Project(2011ZX05043)CNPC Major Science and Technology Project(2013E0502)Innovation Project of PetroChina Research Institute of Exploration and Development(2012Y006).
文摘Oil and gas currently still hold a leading role in the global energy mix.The recent drastic increase in unconventional oil and gas production contributes significantly to strike a balance between the global demand and supply of oil and gas.However,a range of important fundamental questions about the unconventional oil and gas resources have not been adequately answered.Little is known about the distribution and accumulation patterns,as well as the exploration and development characteristics of unconventional oil and gas.The current status of global oil and gas exploration was reviewed and four key theoretical issues regarding the unconventional oil and gas geology were identified:(1)the traditional concept and definition of“petroleum system”needs to be revisited.The concept of a“holistic-process accumulation”model of a“total petroleum system”in petroliferous basins was proposed to analyze the unconventional hydrocarbon accumulation mechanisms from four key aspects of quantitative studies on hydrocarbon generation-expulsion-migration-accumulation processes.(2)The second issue is related to fine-grained sedimentary system and sedimentary facies of tight reservoirs.Through analyzing the relationship between fine-grained sediments and unconventional hydrocarbon accumulation,three research integration areas were put forward.(3)The third issue is on the micro-nano pore system and fluid phase behavior in shales and tight reservoirs.Five aspects of micro-nano pore system were identified to focus on unconventional hydrocarbon research,and the characteristics of micro-nano pore development and fluid phase behavior in micro-nanopores were elucidated.(4)The fourth issue is related to unconventional hydrocarbon accumulation patterns and resource evaluation.Based on the characteristics of unconventional hydrocarbon accumulation,an evaluation system for unconventional hydrocarbon resources was established and optimized.
基金The authors are grateful to Lei Xie,Xiaowei Yang,Bing Shu and Yanni Ma,for their help in sampling and field work.This study was supported by the National Natural Science Foundation of China(Grant No.41302123)the Doctoral Program of Higher Education(Specialized Research Fund)of China(Grant No.20125121130001)the Science Foundation of Education Department of Sichuan Province(Grant No.13ZB0190).
文摘During the past two years the shale gas exploration in Southern Sichuan basin received some exciting achievements.Data of a new appraisal well showed that the gas producrtions of vertical well and horizontal well are^1.5×104 m3/day/well(with maximum^3.5×104 m3/day/well)and^12.5×104 m3/day/well(with maximum^40×104 m3/day/well),respectively,indicating a good gas potential in this area.Eight core samples from the reservoir were investigated by using a carbon sulfur analyzer,microphotometry,x-ray diffractometry,field-emission scanning electron microscopy(FE-SEM),mercury injection porosimetry(MIP),and low-pressure nitrogen adsorption to obtain a better understanding of the reservoir characteristics of the Upper OrdovicianeLower Silurian organic-rich shale.Results show that the total organic carbon(TOC)content ranges from 0.5%to 5.9%,whereas the equivalent vitrinite reflectance(VRr)is between 2.8%and 3.0%.Pores in the studied samples were observed in three modes of occurrence,namely,interparticle pores,intraparticle pores,and intraparticle organic pores.The total porosity(P)ranges from 1.6%to 5.3%,and MIP data sets suggest that pores with throats larger than 20 nm contribute little to the pore volume.Low-pressure N2 adsorption isotherms indicate that the total specific surface area(SBET)ranges from 9.6 m2/g to 18.9 m2/g,and the pore volume(V)ranges from 0.011 cm3/g to 0.020 cm3/g.The plot of dV/dW versus W shows that the fine mesopores(pore size(BJH)<4 nm)mainly contribute to the pore volume.The P,SBET,and V show a good positive correlation with TOC and a weak positive correlation with the total clay mineral content,thus indicating that the nanopores are mainly generated by the decomposition of organic matter.The reservoir characteristics of the Upper OrdovicianeLower Silurian organic-rich shale are comparable with commercial shale gas plays in North America.The sample gas contents with TOC>2%are more than 3.0 m3/ton.The observation can be a good reference for the future exploration and evaluation of reservoir in t
