The deep layer has become an important replacement field for oil and gas exploration,but the formation mechanism of effective reservoirs is unknown,and the distribution of dessert reservoirs is difficult to predict,wh...The deep layer has become an important replacement field for oil and gas exploration,but the formation mechanism of effective reservoirs is unknown,and the distribution of dessert reservoirs is difficult to predict,which seriously affects the discovery of deep resources.In this paper,the reservoir of the first and second members of the Shahejie Formation in the Caofeidian 6-4S area of the Bozhong Depression is taken as an example.Through the comprehensive means such as well-seismic calibration,denudation recovery,source-sink quantitative coupling,basin simulation,microscopic observation,X-ray diffraction,inclusion and thermodynamic analysis,the reservoir formation mechanism of dissolution pores and the favorable area distribution of thermodynamic prediction of dissolution reaction in the study area are carried out.The results show that the dissolution pores are the dominant type,accounting for more than 80%of the total pores.The dissolution reaction between soluble minerals such as feldspar accumulated in the near source and acidic fluids such as organic acids formed in the adjacent strata is the main mechanism for the development of dissolution pores.The organic matter in the adjacent strata is controlled by temperature and pressure during the burial evolution process to form organic acids,and migrates to the adjacent reservoirs for selective dissolution under the action of pressure and other driving forces.The characteristics of thermodynamic parameters(ΔG,which can determine whether feldspar is dissolved)and kinetic parameters(R,indicating the degree of feldspar dissolution)of feldspar dissolution reaction show that the thermodynamic parameters of feldspar dissolution are positively correlated with temperature,and the kinetic parameters are correlated with the concentration of organic acid discharge.The results of thermodynamic and kinetic parameters are coupled with provenance-sedimentary facies-diagenetic facies,and it is predicted that the plane area of TypeⅠfavorable area is 50 km^(2),and the plane area of TypeⅡfavorable area is 62.4 km2.This method provides theoretical reference and method guidance for the prediction of favorable reservoir distribution of deep clastic rocks,and has a good application prospect.展开更多
To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Memb...To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.展开更多
Clastic rock reservoirs in petroliferous basins are generally rich in feldspars. Feldspar dissolution has developed widely in clastic reservoirs, and the resulting secondary pores are crucial in deeply buried reservoi...Clastic rock reservoirs in petroliferous basins are generally rich in feldspars. Feldspar dissolution has developed widely in clastic reservoirs, and the resulting secondary pores are crucial in deeply buried reservoirs. Based on a study of the diagenesis of clastic reservoirs in the Bohai Bay Basin, Tarim Basin, and Pearl River Mouth Basin and physical and numerical simulation experiments of fluid-rock interactions, this paper proposed a successive formation model of secondary pores via feldspar dissolution in deeply buried clastic reservoirs, considering the global research progresses in feldspar dissolution in clastic rocks. Feldspar dissolution can occur from shallow open systems to deep-ultra deep closed systems in petroliferous basins, resulting in the successive formation of secondary pores at different diagenetic stages. The successive mechanism includes three aspects. The first aspect is the succession of corrosive fluids that dissolve minerals. Meteoric freshwater dominates at the Earth’s surface and the early diagenetic A stage. Subsequently, organic acids and COformed via kerogen maturation dominate at the early diagenetic B stage to the middle diagenetic stage. COand organic acids formed via hydrocarbon oxidation in hydrocarbon reservoirs dominate at the middle diagenetic B stage to the late diagenetic stage. The second aspect is the successive formation processes of secondary pores via feldspar dissolution. Large-scale feldspar secondary pores identified in deep reservoirs include secondary pores formed at shallow-medium depths that are subsequently preserved into deep layers, as well as secondary pores formed at deep depths. Existing secondary pores in deeply buried reservoirs are the superposition of successively feldspar dissolution caused by different acids at different stages. The third aspect is a successive change in the feldspar alteration pathways and porosity enhancement/preservation effect. Open to semi-open diagenetic systems are developed from the Earth’s surface to the early diagenetic stage, and feldspar dissolution forms enhanced secondary pores. Nearly closed to closed diagenetic systems develop in the middle to late diagenetic stages, and feldspar dissolution forms redistributional secondary pores. The associated cementation causes compression resistance of the rock, which is favorable for the preservation of secondary pores in deep layers. These new insights extend the formation window of secondary pores in petroliferous basins from the traditional acid-oil generation window to a high-temperature gas generation window after hydrocarbon charging. The proposed model explains the genesis of deep-ultra deep high-quality reservoirs with low-permeability, medium-porosity and dominating feldspar secondary pores, which is significant for hydrocarbon exploration in deep to ultra-deep layers.展开更多
Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore ...Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore in the reservoir rocks.On the basis of thermodynamic phase equilibrium,this study investigates the chemical equilibrium relationships between fluid and various plagioclase and K-feldspar in diagenesis of the sediments,particularly,the impact of temperature and fluid compositions(pH,activity of K+,Na+,Ca2+and so on)on precipitation and dissolution equilibria of feldspars.Feldspar is extremely easily dissolved in the acid pore water with a low salinity when temperature decreases.The dissolution of anorthite end-member of plagioclase is related to the Ca content of the mineral and the fluid,higher Ca either in the mineral or in the fluid,easier dissolution of the feldspar.Moreover,the dissolution of albite end-member of plagioclase is related to Na of both the mineral and fluid,lower Na out of both the mineral and fluid,easier dissolution of the mineral.Similarly,lower-K fluid is more powerful to dissolve K-feldspar than the higher.The anorthite component of plagioclase is most easily dissolved in ground water-rock system,the albite is the secondary,and K-feldspar is the most stable.Selective dissolution of plagioclase occurs in diagenesis because of the plagioclase solid solution that is mainly composed of albite and anorthite end-members,Ca-rich part of which is preferentially dissolved by the pore water,in contrast to the Na-rich parts.Based on investigation of reservoir quality,secondary pore,dissolution structures of feldspar,clay minerals and ground water chemistry of the Kela 2 gas field of Kuqa Depression in the Tarim basin of Western China,we discovered that the secondary pore is very well developed in the highest quality section of the reservoir,and the plagioclase of which was obviously selectively dissolved,in contrast to the overgrowth of K-feldspar.Chemistry of the ground water out of the highest quality section of the reservoir is consistent with the complete dissolution field of anorthite,partial dissolution field of albite component of plagioclase,and the precipitation of K-feldspar on the temperature-logK phase equilibrium diagram drawn from this study.The thermodynamic modeling calculation gave us an insight into formation of the secondary pore within the reservoir,and the dissolution of plagioclase an important cause of the secondary pore.It is assumed that the solvent to dissolve the plagioclase frame grains originated from the origin-enriched compacted fluid acids out of the mudstone buried beneath the top of geopressured zones in the Kuqa Depression.展开更多
基金The National Natural Science Foundation of China under contract Nos U24B2016 and 42202157the National Basic Research Program of China under contract No. KJGG2022-0101+1 种基金the Key Laboratory of Tectonics and Petroleum Resources under contract No. TPR-2023-04CNOOC Technology Project under contract No. KJZH-2023-2105
文摘The deep layer has become an important replacement field for oil and gas exploration,but the formation mechanism of effective reservoirs is unknown,and the distribution of dessert reservoirs is difficult to predict,which seriously affects the discovery of deep resources.In this paper,the reservoir of the first and second members of the Shahejie Formation in the Caofeidian 6-4S area of the Bozhong Depression is taken as an example.Through the comprehensive means such as well-seismic calibration,denudation recovery,source-sink quantitative coupling,basin simulation,microscopic observation,X-ray diffraction,inclusion and thermodynamic analysis,the reservoir formation mechanism of dissolution pores and the favorable area distribution of thermodynamic prediction of dissolution reaction in the study area are carried out.The results show that the dissolution pores are the dominant type,accounting for more than 80%of the total pores.The dissolution reaction between soluble minerals such as feldspar accumulated in the near source and acidic fluids such as organic acids formed in the adjacent strata is the main mechanism for the development of dissolution pores.The organic matter in the adjacent strata is controlled by temperature and pressure during the burial evolution process to form organic acids,and migrates to the adjacent reservoirs for selective dissolution under the action of pressure and other driving forces.The characteristics of thermodynamic parameters(ΔG,which can determine whether feldspar is dissolved)and kinetic parameters(R,indicating the degree of feldspar dissolution)of feldspar dissolution reaction show that the thermodynamic parameters of feldspar dissolution are positively correlated with temperature,and the kinetic parameters are correlated with the concentration of organic acid discharge.The results of thermodynamic and kinetic parameters are coupled with provenance-sedimentary facies-diagenetic facies,and it is predicted that the plane area of TypeⅠfavorable area is 50 km^(2),and the plane area of TypeⅡfavorable area is 62.4 km2.This method provides theoretical reference and method guidance for the prediction of favorable reservoir distribution of deep clastic rocks,and has a good application prospect.
基金Supported by the National Natural Science Foundation of China(42202176)CNPC-Southwest University of Petroleum Innovation Consortium Cooperation Project(2020CX050103).
文摘To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41872140, 41821002, 41911530189)the National Major Science and Technology Special Grant (Grant No. 2016ZX05006-007)+2 种基金the Special Fund for Taishan Scholar Project (Grant No. tsqn201909061)the Fundamental Research Funds for the Central Universities (Grant No. 20CX06067A)the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao) (Grant No. 2021QNLM020001)。
文摘Clastic rock reservoirs in petroliferous basins are generally rich in feldspars. Feldspar dissolution has developed widely in clastic reservoirs, and the resulting secondary pores are crucial in deeply buried reservoirs. Based on a study of the diagenesis of clastic reservoirs in the Bohai Bay Basin, Tarim Basin, and Pearl River Mouth Basin and physical and numerical simulation experiments of fluid-rock interactions, this paper proposed a successive formation model of secondary pores via feldspar dissolution in deeply buried clastic reservoirs, considering the global research progresses in feldspar dissolution in clastic rocks. Feldspar dissolution can occur from shallow open systems to deep-ultra deep closed systems in petroliferous basins, resulting in the successive formation of secondary pores at different diagenetic stages. The successive mechanism includes three aspects. The first aspect is the succession of corrosive fluids that dissolve minerals. Meteoric freshwater dominates at the Earth’s surface and the early diagenetic A stage. Subsequently, organic acids and COformed via kerogen maturation dominate at the early diagenetic B stage to the middle diagenetic stage. COand organic acids formed via hydrocarbon oxidation in hydrocarbon reservoirs dominate at the middle diagenetic B stage to the late diagenetic stage. The second aspect is the successive formation processes of secondary pores via feldspar dissolution. Large-scale feldspar secondary pores identified in deep reservoirs include secondary pores formed at shallow-medium depths that are subsequently preserved into deep layers, as well as secondary pores formed at deep depths. Existing secondary pores in deeply buried reservoirs are the superposition of successively feldspar dissolution caused by different acids at different stages. The third aspect is a successive change in the feldspar alteration pathways and porosity enhancement/preservation effect. Open to semi-open diagenetic systems are developed from the Earth’s surface to the early diagenetic stage, and feldspar dissolution forms enhanced secondary pores. Nearly closed to closed diagenetic systems develop in the middle to late diagenetic stages, and feldspar dissolution forms redistributional secondary pores. The associated cementation causes compression resistance of the rock, which is favorable for the preservation of secondary pores in deep layers. These new insights extend the formation window of secondary pores in petroliferous basins from the traditional acid-oil generation window to a high-temperature gas generation window after hydrocarbon charging. The proposed model explains the genesis of deep-ultra deep high-quality reservoirs with low-permeability, medium-porosity and dominating feldspar secondary pores, which is significant for hydrocarbon exploration in deep to ultra-deep layers.
基金Much content and data of this study came from the Fundamental Research Special Support Project of Ministry of ScienceTechnology of China(Grant No.2001CB209104)This work was also supported by the National Natural Science Foundation of China(Grant Nos.49902016 and 40272032).
文摘Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore in the reservoir rocks.On the basis of thermodynamic phase equilibrium,this study investigates the chemical equilibrium relationships between fluid and various plagioclase and K-feldspar in diagenesis of the sediments,particularly,the impact of temperature and fluid compositions(pH,activity of K+,Na+,Ca2+and so on)on precipitation and dissolution equilibria of feldspars.Feldspar is extremely easily dissolved in the acid pore water with a low salinity when temperature decreases.The dissolution of anorthite end-member of plagioclase is related to the Ca content of the mineral and the fluid,higher Ca either in the mineral or in the fluid,easier dissolution of the feldspar.Moreover,the dissolution of albite end-member of plagioclase is related to Na of both the mineral and fluid,lower Na out of both the mineral and fluid,easier dissolution of the mineral.Similarly,lower-K fluid is more powerful to dissolve K-feldspar than the higher.The anorthite component of plagioclase is most easily dissolved in ground water-rock system,the albite is the secondary,and K-feldspar is the most stable.Selective dissolution of plagioclase occurs in diagenesis because of the plagioclase solid solution that is mainly composed of albite and anorthite end-members,Ca-rich part of which is preferentially dissolved by the pore water,in contrast to the Na-rich parts.Based on investigation of reservoir quality,secondary pore,dissolution structures of feldspar,clay minerals and ground water chemistry of the Kela 2 gas field of Kuqa Depression in the Tarim basin of Western China,we discovered that the secondary pore is very well developed in the highest quality section of the reservoir,and the plagioclase of which was obviously selectively dissolved,in contrast to the overgrowth of K-feldspar.Chemistry of the ground water out of the highest quality section of the reservoir is consistent with the complete dissolution field of anorthite,partial dissolution field of albite component of plagioclase,and the precipitation of K-feldspar on the temperature-logK phase equilibrium diagram drawn from this study.The thermodynamic modeling calculation gave us an insight into formation of the secondary pore within the reservoir,and the dissolution of plagioclase an important cause of the secondary pore.It is assumed that the solvent to dissolve the plagioclase frame grains originated from the origin-enriched compacted fluid acids out of the mudstone buried beneath the top of geopressured zones in the Kuqa Depression.
