In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make...In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make depleted oil and gas reservoirs unsuitable for gas storage.In order to effectively evaluate the sealing of faults in caprock above depleted reservoir and provide a basis for a reasonable selection of injection time and location for gas storage,this paper comprehensively considers fault slip potential(FSP)and fault tensile potential(FTP),and establishes a fault sealing evaluation model in caprock above depleted reservoir.The influences of distance of fault from reservoir top,reservoir pressure depletion degree,cap mechanical property,fault occurrence,fault frictional property and in-situ stress anisotropy in caprock on different types of FSP and FTP are analyzed.The results show that for normal faults,reverse faults,and strike-slip faults,FTP increases with reservoir depletion and does not cause tensile failure,among which FTP is the smallest for normal faults.FSP is the key to controlling fault sealing in caprock above depleted reservoir.For reverse faults and strike-slip faults,in the early stage of reservoir depletion,the FsP is larger when the fault is farther away from the top of the reservoir,while normal faults are the opposite.When the normal fault is closer to the top of the reservoir,the cap poisson ratio is smaller,the Biot's coefficient is larger,the internal friction coefficient of the fault is smaller,the inherent shear strength of the fault is smaller,σH/σv is smaller,σh/σv is smaller,45°<β<75°,α=0° or α=180°,the FSP is larger with the reservoir depletion,and the shear failure of the fault is the most likely.At this time,the reservoir pressure should be strictly controlled not to be too small,so that it can be suitable for the construction of gas storage.Under other conditions,the possibility of shear failure of the caprock is less.For reverse faults and strike-slip faults,when is smaller,the FSP decreases first and then increases with reservoir depletion.Although the possibility of shear failure decreases in the initial stage of reservoir depletion,it increases in the later stage.The research results can provide a theoretical basis for the reconstruction of underground gas storage.展开更多
Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consid...Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consider changes in temperature and pressure conditions,which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling.Triaxial stress-strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperaturepressure action and isothermal-variable pressure action on the basis of sample feasibility analysis.According to research,the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions,and it becomes more ductile.This reduces the amount of time it takes for the rock to transition from brittle to plastic.When temperature is taken into account,both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower,and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization.The sealing ability under the temperature-pressure coupling is more in line with the actual geological context when the application results of the Well#ZS5 are compared.This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.展开更多
The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon sou...The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon source development characteristics of the Meso-Neoproterozoic and its overlying strata,as well as the formation contact relationships,lithology characteristics and exploratory drilling data,it is recognized that the Meso-Neoproterozoic contains two types of petroleum accumulation assemblage,that is,the“self-sourced indigenous”and“upper source rock-lower reservoir”assemblages.The former is mainly controlled by the development and distribution of source rocks of the Changcheng System,with the Lower Cambrian shale sequence as its caprock.The later is controlled by the superposition between the Meso-Neoproterozoic and its overlying source rocks and this assemblage is mainly distributed in Hangjinqi and Pingliang areas with the Carboniferous-Permian shale sequence as its caprock.The dynamic evaluation on the displacement pressure serves to reconstruct the displacement pressure history of the caprock.The results show that the shale sequence of the Cambrian Maozhuang Formation in well XY 1 in the southern Ordos Basin has possibly acquired the ability of sealing natural gas since the early of Late Triassic.Its displacement pressure increased rapidly up to 20 MPa during the Late Triassic-Jurassic and keeps at 9.2 MPa at present,indicating fair sealing ability.The Carboniferous-Permian caprocks in Hangjinqi area could have acquired the ability to seal natural gas in the Late Jurassic-Early Cretaceous,and the present-day displacement pressure is 9e12 MPa,indicating good sealing ability.The upper Paleozoic caprock in Pingliang area has been able to seal natural gas since the Early Jurassic,with a maximum displacement pressure of 23 MPa during the Cretaceous period and a current value of 17 e20 MPa,indicative of strong ability to seal natural gas.The sealing ability of caprocks of both the“selfsourced indigenous”and“upper source rock-lower reservoir”assemblages has come into being earlier than or at least no later than the peak gas generation of the source rocks and therefore the caprocks are dynamically effective in geohistory.The Meso-Neoproterozoic reservoirs in the Ordos Basin are well preserved and probabally of better potential for exploration in terms of the caprock-source rock combination.展开更多
Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted b...Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted by the buoyant CO2plume, CO2gradually penetrates into the caprock. The CO2penetration depth into a caprock layer can be used to measure the caprock sealing efficiency and becomes the key issue to the assessment of caprock sealing efficiency. On the other hand, our numerical simulations on a caprock layer have revealed that a square root law for time and pore pressure exists for the CO2penetration into the caprock layer. Based on this finding, this study proposes a simple approach to estimate the CO2penetration depth into a caprock layer. This simple approach is initially developed to consider the speed of CO2invading front. It explicitly expresses the penetration depth with pressuring time, pressure difference and pressure magnitude. This simple approach is then used to fit three sets of experimental data and good fittings are observed regardless of pressures, strengths of porous media, and pore fluids(water,hydrochloric acid, and carbonic acid). Finally, theoretical analyses are conducted to explore those factors affecting CO2penetration depth. The effects of capillary pressure, gas sorption induced swelling, and fluid property are then included in this simple approach. These results show that this simple approach can predict the penetration depth into a caprock layer with sufficient accuracy, even if complicated interactions in penetration process are not explicitly expressed in this simple formula.展开更多
Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi F...Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi Formation gypsolyte rock that seals significant petroleum in the Kashi Sag of Tarim Basin had been revealed via X-ray diffraction and triaxial compression test. The results indicate the Artashi Formation can be lithologically divided into the lower and upper lithologic members. The lower member comprises gypsum as the dominant mineral, and the cohesion and friction coefficient are 8 MPa and 0.315, respectively. Similarly, the upper lithologic member consists mainly of anhydrite at the cohesion and coefficient of internal friction values of 18 MPa and 0.296. Given that the failure criterion and brittle-ductile transition factors during burial, the sealing integrity of Artashi Formation can be quantized for seven different stages. The reservoirs at the bottom of Artashi Formation caprock buried from 2285 m to 3301 m are expected to be the most favorable exploration target in the Kashi Sag.展开更多
Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sands...Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sandstone,Permian mudstone and Permian siltstone were collected and tested using experimental methods of microstructure observation,pore structure measurement and diffusion properties determination.Results indicate that with denser structures,lower porosities,much more developed micropores/transition pores and higher pore/throat ratios,mudstone and siltstone have the more ideal sealing capacities for CBM preservation when comparing to other kinds of caprocks;the methane diffusion coefficients of mudstone/siltstone are about 6 times higher than sandstone and almost 90 times higher than clayrock/redbeds.To further estimate the CBM escape through caprocks,a one-dimensional CBM diffusion model is derived.Modeling calculation result demonstrates that under the same thickness,the CBM sealing abilities of mudstone/siltstone are almost 100 times higher than those of clayrock/redbeds,and nearly 17 times higher than sandstone,which indicates that the coal seam below caprocks like clayrock,redbeds or sandstone may suffer stronger CBM diffusion effect than that below mudstone or siltstone.Such conclusion is verified by the case study from III3 District,Xutuan Colliery,where the coal seam capped by Paleogene redbeds has a much lower CBM content than that capped by the Permian strata like mudstone,siltstone and sandstone.展开更多
The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this ...The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this paper, we use the Amplitude versus offset （AVO） seismic technique to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The essence of this technique is to detect the variations of the reservoir bed physical properties by monitoring the variations of the reflection coefficient of seismic waves upon the interfaces between different lithologies. Generally it is used to indicate hydrocarbon directly. For the hydrocarbon concentration sealing caprocks, the change of hydrocarbon concentration may cause the change of physical properties of the caprocks. Therefore it is possible to evaluate the hydrocarbon concentration sealing ability of the caprocks by AVO. This paper presents a case study using AVO to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The result shows that this method is helpful for the exploration of the region.展开更多
The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.O...The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.Of these,carbon isotope and biomarkers or chemical fossils are new scopes in petroleum geology especially in correlation.The member 1 of Gachsaran formation can be divided into 6 keybeds,among them the B keybed is展开更多
Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the ...Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the formation of these gasfields and their development laws have already been discussed in a large number of literatures,but the relationship between over pressure and the formation of this kind of gasfields is still less researched.In this regard,this paperfirstly analyzed the gas reservoir development law,sealing conditions and over pressure char-acteristics of deep and ultra-deep super-large gasfields.Then,the formation mechanisms of deep and ultra-deep over pressure caprocks were investigated and the development law of deep and ultra-deep super-large gasfields and their relationship with over pressure caprocks were discussed.Finally,the favorable areas for the next exploration of deep and ultra-deep natural gas were pointed out.And the following research results were obtained.First,the formation of deep and ultra-deep super-large gasfields is closely related to the development of over pressure caprocks.Over pressure caprock is a necessary condition for the formation of deep and ultra-deep super-large gasfields,and there are three over pressure formation mechanisms,including pressure seal of salt-gypsum layer,pressure seal of residual uplift and pressure seal of hydrocarbon-generating pressurization.Second,as for deep and ultra-deep over pressure caprocks and super-large gasfields,there are four reservoirecaprock assemblage modes under different pressure environments,i.e.,over pressure salt-gypsum seal and over pressure super-large gasfield(Type I),internal over pressure compartment and over pressure super-large gasfield(Type II),high-pressure argillaceous shale seal at the bottom of over pressure compartment and normal-pressure super-larger gasfield(Type III),and over pressure source rock seal and normal-pressure super-larger gasfield(Type IV).In conclusion,there are Type I super-large gasfields in the Kuqa Depression of the Tarim Basin,types II and III in the Junggar Basin,types IeIV in the Sichuan Basin and Type IV in the Bohai Bay Basin.展开更多
Precipitation or dissolution due to geochemical reactions has been observed in the caprocks for CO_(2)geosequestration.Geochemical reactions modify the caprock sealing efficiency with self-limiting or self-enhancement...Precipitation or dissolution due to geochemical reactions has been observed in the caprocks for CO_(2)geosequestration.Geochemical reactions modify the caprock sealing efficiency with self-limiting or self-enhancement.However,the effect of this modification on the caprock sealing efficiency has not been fully investigated through multiphysical-geochemical coupling analysis.In this study,a multiphysical-geochemical coupling model was proposed to analyze caprock sealing efficiency.This coupling model considered the full couplings of caprock deformation,two-phase flow,CO_(2)concentration diffusion,geochemical reaction,and CO_(2)sorption.The two-phase flow only occurs in the fracture network and the CO_(2)may partially dissolve into water and diffuse through the concentration difference.The dissolved CO_(2)has geochemical reactions with some critical minerals,thus altering flow channels.The CO_(2)in the fracture network diffuses into matrix,causing the matrix swelling.This fully coupling model was validated with a penetration experiment on a cement cube and compared with two other models for CO_(2)storage plumes.Finally,the effects of geochemical reactions on penetration depth and pore pressure were studied through parametric study.The numerical simulations reveal that the coupling of geochemical reactions and matrix diffusion significantly affect the caprock sealing efficiency.Geochemical reactions occur at a short time after the arrival of CO_(2)concentration and modify the fracture porosity.The CO_(2)diffusion into the matrix requires a much longer time and mainly induces matrix swelling.These effects may produce selfenhancement or self-limiting depending on the flow rate in the fracture network,thus significantly modifying caprock sealing efficiency.展开更多
Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumula...Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumulation with reservoir-forming assemblage as the unit.In the Persian Gulf Basin,the hydrocarbon-generating centers of source rocks of different geological ages and the hydrocarbon rich zones migrate in a clockwise direction around the Ghawar Oilfield in the Central Arabian Subbasin.Horizontally,the overall distribution pattern is orderly,showing“oil in the west and gas in the east”,and“large oil and gas fields dense in the basin center and sparse at the basin edges”.Vertically,the extents of petroleum system compounding and sources mixing increase from west to east,the pattern of tectonic strength(weak in the west and strong in the east)forming the distribution characteristics of“gas rich in the Paleozoic,oil rich in the Mesozoic,and both oil and gas rich in the Cenozoic”.The large scale accumulation and orderly distribution of oil and gas in the Persian Gulf Basin are controlled by three factors:(1)Multiple sets of giant hydrocarbon kitchens provide a resource base for near-source reservoir-forming assemblages.The short-distance lateral migration determines the oil and gas enrichment in and around the distribution area of effective source rocks.(2)The anhydrite caprocks in the platform area are thin but have experienced weak late-stage tectonic activities.Their good sealing performance makes it difficult for oil and gas to migrate vertically to shallow layers through them.The thrust faults and high-angle fractures formed by intense tectonic activities of the Zagros Orogenic Belt connect multiple source-reservoir assemblages.However,the Neogene Gachsaran Formation gypsum-salt rocks are thick and highly plastic,generally with good sealing performance,so large-scale oil and gas accumulations are still formed beneath the salt;(3)Each set of reservoir-forming assemblages is well matched in time and space in terms of the development of source rocks and reservoir-caprock assemblages,the maturation and hydrocarbon generation of source rocks,and the formation of traps,thus resulting in abundant multi layer hydrocarbon accumulations.At present,the Persian Gulf Basin is still in the stage of structural trap exploration.The pre-salt prospective traps in effective hydrocarbon kitchens remain the first choice.The areas with significant changes in Mesozoic sedimentary facies have the conditions to form large scale lithologic oil and gas reservoirs.The deep Paleozoic conventional oil and gas reservoirs and the Lower Silurian Qusaiba Member shale gas have great exploration potential and are expected to become important reserve growth areas in the future.展开更多
基金National Natural Science Foundation of China(52074224)Key Research and Development Program of Shaanxi Province(2023-YBGY-312).
文摘In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make depleted oil and gas reservoirs unsuitable for gas storage.In order to effectively evaluate the sealing of faults in caprock above depleted reservoir and provide a basis for a reasonable selection of injection time and location for gas storage,this paper comprehensively considers fault slip potential(FSP)and fault tensile potential(FTP),and establishes a fault sealing evaluation model in caprock above depleted reservoir.The influences of distance of fault from reservoir top,reservoir pressure depletion degree,cap mechanical property,fault occurrence,fault frictional property and in-situ stress anisotropy in caprock on different types of FSP and FTP are analyzed.The results show that for normal faults,reverse faults,and strike-slip faults,FTP increases with reservoir depletion and does not cause tensile failure,among which FTP is the smallest for normal faults.FSP is the key to controlling fault sealing in caprock above depleted reservoir.For reverse faults and strike-slip faults,in the early stage of reservoir depletion,the FsP is larger when the fault is farther away from the top of the reservoir,while normal faults are the opposite.When the normal fault is closer to the top of the reservoir,the cap poisson ratio is smaller,the Biot's coefficient is larger,the internal friction coefficient of the fault is smaller,the inherent shear strength of the fault is smaller,σH/σv is smaller,σh/σv is smaller,45°<β<75°,α=0° or α=180°,the FSP is larger with the reservoir depletion,and the shear failure of the fault is the most likely.At this time,the reservoir pressure should be strictly controlled not to be too small,so that it can be suitable for the construction of gas storage.Under other conditions,the possibility of shear failure of the caprock is less.For reverse faults and strike-slip faults,when is smaller,the FSP decreases first and then increases with reservoir depletion.Although the possibility of shear failure decreases in the initial stage of reservoir depletion,it increases in the later stage.The research results can provide a theoretical basis for the reconstruction of underground gas storage.
基金funded by the National Natural Science Foundation of China(Grant No.42172147)PetroChina Major Science and Technology Project(Grant No.ZD2019-183-002).
文摘Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consider changes in temperature and pressure conditions,which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling.Triaxial stress-strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperaturepressure action and isothermal-variable pressure action on the basis of sample feasibility analysis.According to research,the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions,and it becomes more ductile.This reduces the amount of time it takes for the rock to transition from brittle to plastic.When temperature is taken into account,both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower,and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization.The sealing ability under the temperature-pressure coupling is more in line with the actual geological context when the application results of the Well#ZS5 are compared.This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.
基金supported by the National Key R&D Program of China grant(2017YFC0603105).
文摘The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon source development characteristics of the Meso-Neoproterozoic and its overlying strata,as well as the formation contact relationships,lithology characteristics and exploratory drilling data,it is recognized that the Meso-Neoproterozoic contains two types of petroleum accumulation assemblage,that is,the“self-sourced indigenous”and“upper source rock-lower reservoir”assemblages.The former is mainly controlled by the development and distribution of source rocks of the Changcheng System,with the Lower Cambrian shale sequence as its caprock.The later is controlled by the superposition between the Meso-Neoproterozoic and its overlying source rocks and this assemblage is mainly distributed in Hangjinqi and Pingliang areas with the Carboniferous-Permian shale sequence as its caprock.The dynamic evaluation on the displacement pressure serves to reconstruct the displacement pressure history of the caprock.The results show that the shale sequence of the Cambrian Maozhuang Formation in well XY 1 in the southern Ordos Basin has possibly acquired the ability of sealing natural gas since the early of Late Triassic.Its displacement pressure increased rapidly up to 20 MPa during the Late Triassic-Jurassic and keeps at 9.2 MPa at present,indicating fair sealing ability.The Carboniferous-Permian caprocks in Hangjinqi area could have acquired the ability to seal natural gas in the Late Jurassic-Early Cretaceous,and the present-day displacement pressure is 9e12 MPa,indicating good sealing ability.The upper Paleozoic caprock in Pingliang area has been able to seal natural gas since the Early Jurassic,with a maximum displacement pressure of 23 MPa during the Cretaceous period and a current value of 17 e20 MPa,indicative of strong ability to seal natural gas.The sealing ability of caprocks of both the“selfsourced indigenous”and“upper source rock-lower reservoir”assemblages has come into being earlier than or at least no later than the peak gas generation of the source rocks and therefore the caprocks are dynamically effective in geohistory.The Meso-Neoproterozoic reservoirs in the Ordos Basin are well preserved and probabally of better potential for exploration in terms of the caprock-source rock combination.
基金the financial support from the Creative Research and Development Group Program of Jiangsu Province(2014-27)the National Science Fund for Distinguished Young Scholars(Grant No.51125017)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD2014)
文摘Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted by the buoyant CO2plume, CO2gradually penetrates into the caprock. The CO2penetration depth into a caprock layer can be used to measure the caprock sealing efficiency and becomes the key issue to the assessment of caprock sealing efficiency. On the other hand, our numerical simulations on a caprock layer have revealed that a square root law for time and pore pressure exists for the CO2penetration into the caprock layer. Based on this finding, this study proposes a simple approach to estimate the CO2penetration depth into a caprock layer. This simple approach is initially developed to consider the speed of CO2invading front. It explicitly expresses the penetration depth with pressuring time, pressure difference and pressure magnitude. This simple approach is then used to fit three sets of experimental data and good fittings are observed regardless of pressures, strengths of porous media, and pore fluids(water,hydrochloric acid, and carbonic acid). Finally, theoretical analyses are conducted to explore those factors affecting CO2penetration depth. The effects of capillary pressure, gas sorption induced swelling, and fluid property are then included in this simple approach. These results show that this simple approach can predict the penetration depth into a caprock layer with sufficient accuracy, even if complicated interactions in penetration process are not explicitly expressed in this simple formula.
基金Project(41672121)supported by the National Natural Science Foundation of ChinaProject(D1438)supported by the China Geological Survey
文摘Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi Formation gypsolyte rock that seals significant petroleum in the Kashi Sag of Tarim Basin had been revealed via X-ray diffraction and triaxial compression test. The results indicate the Artashi Formation can be lithologically divided into the lower and upper lithologic members. The lower member comprises gypsum as the dominant mineral, and the cohesion and friction coefficient are 8 MPa and 0.315, respectively. Similarly, the upper lithologic member consists mainly of anhydrite at the cohesion and coefficient of internal friction values of 18 MPa and 0.296. Given that the failure criterion and brittle-ductile transition factors during burial, the sealing integrity of Artashi Formation can be quantized for seven different stages. The reservoirs at the bottom of Artashi Formation caprock buried from 2285 m to 3301 m are expected to be the most favorable exploration target in the Kashi Sag.
基金Project(2016YFC0801608) supported by the National Key Research and Development Plan,ChinaProject(51574148) supported by the National Natural Science Foundation of China
文摘Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sandstone,Permian mudstone and Permian siltstone were collected and tested using experimental methods of microstructure observation,pore structure measurement and diffusion properties determination.Results indicate that with denser structures,lower porosities,much more developed micropores/transition pores and higher pore/throat ratios,mudstone and siltstone have the more ideal sealing capacities for CBM preservation when comparing to other kinds of caprocks;the methane diffusion coefficients of mudstone/siltstone are about 6 times higher than sandstone and almost 90 times higher than clayrock/redbeds.To further estimate the CBM escape through caprocks,a one-dimensional CBM diffusion model is derived.Modeling calculation result demonstrates that under the same thickness,the CBM sealing abilities of mudstone/siltstone are almost 100 times higher than those of clayrock/redbeds,and nearly 17 times higher than sandstone,which indicates that the coal seam below caprocks like clayrock,redbeds or sandstone may suffer stronger CBM diffusion effect than that below mudstone or siltstone.Such conclusion is verified by the case study from III3 District,Xutuan Colliery,where the coal seam capped by Paleogene redbeds has a much lower CBM content than that capped by the Permian strata like mudstone,siltstone and sandstone.
文摘The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this paper, we use the Amplitude versus offset （AVO） seismic technique to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The essence of this technique is to detect the variations of the reservoir bed physical properties by monitoring the variations of the reflection coefficient of seismic waves upon the interfaces between different lithologies. Generally it is used to indicate hydrocarbon directly. For the hydrocarbon concentration sealing caprocks, the change of hydrocarbon concentration may cause the change of physical properties of the caprocks. Therefore it is possible to evaluate the hydrocarbon concentration sealing ability of the caprocks by AVO. This paper presents a case study using AVO to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The result shows that this method is helpful for the exploration of the region.
文摘The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.Of these,carbon isotope and biomarkers or chemical fossils are new scopes in petroleum geology especially in correlation.The member 1 of Gachsaran formation can be divided into 6 keybeds,among them the B keybed is
基金supported by the Special and Significant Project of National Research Council of Science and Technology"Evaluation of Hydrocarbon Accumulation,Distribution Law and Favorable Areas in the Foreland Thrust Belt and Complex Structure Area"(No.:2016ZX05003-002).
文摘Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the formation of these gasfields and their development laws have already been discussed in a large number of literatures,but the relationship between over pressure and the formation of this kind of gasfields is still less researched.In this regard,this paperfirstly analyzed the gas reservoir development law,sealing conditions and over pressure char-acteristics of deep and ultra-deep super-large gasfields.Then,the formation mechanisms of deep and ultra-deep over pressure caprocks were investigated and the development law of deep and ultra-deep super-large gasfields and their relationship with over pressure caprocks were discussed.Finally,the favorable areas for the next exploration of deep and ultra-deep natural gas were pointed out.And the following research results were obtained.First,the formation of deep and ultra-deep super-large gasfields is closely related to the development of over pressure caprocks.Over pressure caprock is a necessary condition for the formation of deep and ultra-deep super-large gasfields,and there are three over pressure formation mechanisms,including pressure seal of salt-gypsum layer,pressure seal of residual uplift and pressure seal of hydrocarbon-generating pressurization.Second,as for deep and ultra-deep over pressure caprocks and super-large gasfields,there are four reservoirecaprock assemblage modes under different pressure environments,i.e.,over pressure salt-gypsum seal and over pressure super-large gasfield(Type I),internal over pressure compartment and over pressure super-large gasfield(Type II),high-pressure argillaceous shale seal at the bottom of over pressure compartment and normal-pressure super-larger gasfield(Type III),and over pressure source rock seal and normal-pressure super-larger gasfield(Type IV).In conclusion,there are Type I super-large gasfields in the Kuqa Depression of the Tarim Basin,types II and III in the Junggar Basin,types IeIV in the Sichuan Basin and Type IV in the Bohai Bay Basin.
基金National Natural Science Foundation of China,Grant/Award Number:51674246Creative Research and Development Group Program of Jiangsu Province,Grant/Award Number:2014-27。
文摘Precipitation or dissolution due to geochemical reactions has been observed in the caprocks for CO_(2)geosequestration.Geochemical reactions modify the caprock sealing efficiency with self-limiting or self-enhancement.However,the effect of this modification on the caprock sealing efficiency has not been fully investigated through multiphysical-geochemical coupling analysis.In this study,a multiphysical-geochemical coupling model was proposed to analyze caprock sealing efficiency.This coupling model considered the full couplings of caprock deformation,two-phase flow,CO_(2)concentration diffusion,geochemical reaction,and CO_(2)sorption.The two-phase flow only occurs in the fracture network and the CO_(2)may partially dissolve into water and diffuse through the concentration difference.The dissolved CO_(2)has geochemical reactions with some critical minerals,thus altering flow channels.The CO_(2)in the fracture network diffuses into matrix,causing the matrix swelling.This fully coupling model was validated with a penetration experiment on a cement cube and compared with two other models for CO_(2)storage plumes.Finally,the effects of geochemical reactions on penetration depth and pore pressure were studied through parametric study.The numerical simulations reveal that the coupling of geochemical reactions and matrix diffusion significantly affect the caprock sealing efficiency.Geochemical reactions occur at a short time after the arrival of CO_(2)concentration and modify the fracture porosity.The CO_(2)diffusion into the matrix requires a much longer time and mainly induces matrix swelling.These effects may produce selfenhancement or self-limiting depending on the flow rate in the fracture network,thus significantly modifying caprock sealing efficiency.
基金Supported by the CNPC Major Science and Technology Project(2023ZZ07).
文摘Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumulation with reservoir-forming assemblage as the unit.In the Persian Gulf Basin,the hydrocarbon-generating centers of source rocks of different geological ages and the hydrocarbon rich zones migrate in a clockwise direction around the Ghawar Oilfield in the Central Arabian Subbasin.Horizontally,the overall distribution pattern is orderly,showing“oil in the west and gas in the east”,and“large oil and gas fields dense in the basin center and sparse at the basin edges”.Vertically,the extents of petroleum system compounding and sources mixing increase from west to east,the pattern of tectonic strength(weak in the west and strong in the east)forming the distribution characteristics of“gas rich in the Paleozoic,oil rich in the Mesozoic,and both oil and gas rich in the Cenozoic”.The large scale accumulation and orderly distribution of oil and gas in the Persian Gulf Basin are controlled by three factors:(1)Multiple sets of giant hydrocarbon kitchens provide a resource base for near-source reservoir-forming assemblages.The short-distance lateral migration determines the oil and gas enrichment in and around the distribution area of effective source rocks.(2)The anhydrite caprocks in the platform area are thin but have experienced weak late-stage tectonic activities.Their good sealing performance makes it difficult for oil and gas to migrate vertically to shallow layers through them.The thrust faults and high-angle fractures formed by intense tectonic activities of the Zagros Orogenic Belt connect multiple source-reservoir assemblages.However,the Neogene Gachsaran Formation gypsum-salt rocks are thick and highly plastic,generally with good sealing performance,so large-scale oil and gas accumulations are still formed beneath the salt;(3)Each set of reservoir-forming assemblages is well matched in time and space in terms of the development of source rocks and reservoir-caprock assemblages,the maturation and hydrocarbon generation of source rocks,and the formation of traps,thus resulting in abundant multi layer hydrocarbon accumulations.At present,the Persian Gulf Basin is still in the stage of structural trap exploration.The pre-salt prospective traps in effective hydrocarbon kitchens remain the first choice.The areas with significant changes in Mesozoic sedimentary facies have the conditions to form large scale lithologic oil and gas reservoirs.The deep Paleozoic conventional oil and gas reservoirs and the Lower Silurian Qusaiba Member shale gas have great exploration potential and are expected to become important reserve growth areas in the future.
