In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oi...In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.展开更多
A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery i...A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.展开更多
With the continuous deepening of natural gas exploration,the quality of discovered resources gets worse and exploration targets are getting more and more complicated,so it is necessary to develop and improve natural g...With the continuous deepening of natural gas exploration,the quality of discovered resources gets worse and exploration targets are getting more and more complicated,so it is necessary to develop and improve natural gas geological theories continuously in order to tap and discover more natural gas resources.Therefore,geological theories on the formation of large gas fields were studied during the 12th Five-Year Plan period and the following progresses were mainly achieved.(1)Gas generation modes were established of oil cracking and highly evolved coal-measure source rocks in different geologic conditions.(2)A model was set up for evaluating quantitatively the hydrocarbon expulsion and detainment of various source rocks with different abundance.(3)Natural gas genesis identification chart was built up with multiple parameters and indexes.(4)Two carbonate rock sedimentation patterns and two tight sandstone sedimentation patterns were established.(5)A new method was developed for evaluating caprockereservoir displacement pressure difference of immediate caprocks.(6)The hydrocarbon accumulation pattern of large gas fields was established and their main controlling factors and distribution laws were summarized.Then,the natural gas exploration theories were deepened in the following five fields and their application achievements are remarkable.First,the hydrocarbon-accumulation geological theory used for large ancient carbonate gas fields was innovatively understood to promote the discovery and confirmation of the Anyue supergiant gas field in the Sichuan Basin.Second,the hydrocarbon-accumulation geological theory suitable for large tight sandstone gas fields was developed to guide the exploration of tight sandstone gas in the Ordos and Songliao basins.Third,the hydrocarbon-accumulation theory of platform margin reefs was deepened to expand the exploration of platform margin reef gas in the Sichuan Basin.Fourth,the hydrocarbon accumulation mechanism and enrichment theory of large condensate gas reservoirs were deepened to guide the exploration of large condensate gas reservoirs in the Tarim Basin.And fifth,the exploration theory of volcanic gas reservoirs with hydrocarbon-generation fault troughs as basic units was completed to realize the strategic replacement of volcanic gas reservoir exploration.展开更多
To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model cons...To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model considered closed boundaries at both the top and bottom,as well as an external boundary with infinite,closed,or constant pressure on the horizontal plane.We took the bi-zonal composite model as an example to carry out concrete analysis.Various contemporary mathematical techniques,including Laplace integral transformation,separation of variables,and eigenfunction methods,were employed to solve the model.The pressure solution in real space was obtained through Duhamel's principle and Stehfest numerical inversion,then analytical curves created,and flow stages were defined for a slanted well in a bi-zonal composite reservoir.In addition,we performed a sensitivity analysis on some parameters affecting the curves.For a tri-zonal composite model,we also plotted the well-test curves and categorized them.Finally,we validated the model through the interpretation of an example well.The results show that the fluid flow of a slanted well in a bi-zonal composite reservoir can be divided into seven main stages,including wellbore storage effect(WSE)stage,skin effect(SE)stage,linear flow(LF)stage,radial flow(RF)stage of the 1st zone,transitional flow(TF)stage from the 1st to the 2nd zone,RF stage of the 2nd zone,and the external boundary response stage.The position of the pressure curve at the SE stage and LF stage decreases as the length and inclination angle increase.Correspondingly,the pressure curve at the RF stage of the 2nd zone and external boundary response stage decreases with increasing mobility ratio.Furthermore,as the radius of the 1st zone increases,the pressure curve at the RF stage of the 1st zone and the TF stage shifts towards the right.The established model and plotted curves provide a theoretical basis for further studies on the flow behavior of slanted wells in composite reservoirs.展开更多
In this paper,the shale of Upper Ordovician Wufeng Fm-Lower Silurian Longmaxi Fm was taken as an example to reveal the distribution patterns and the main sedimentation controlling factors of high-quality shale in the ...In this paper,the shale of Upper Ordovician Wufeng Fm-Lower Silurian Longmaxi Fm was taken as an example to reveal the distribution patterns and the main sedimentation controlling factors of high-quality shale in the Upper Yangtze region.This study was made from the aspects of plate movement,fluctuation of sea level,palaeo-productivity,deposition rate and paleogeographic environment,based on the field outcrop sections and drilling data of the southern Sichuan Basin,together with geochemical element testing and biostratigraphical analysis results.The following findings were obtained.First,the collision and joint of Yangtze Plate and its periphery plates and the intra-plate deformation were gentle in the early stage,strong in the late stage,gentle in northwest and strong in southeast,so the sedimentation center in the Upper Yangtze region migrated to the northwest and the closure of sea area in the southern Sichuan Basin changed from weak in early stages to strong in late stages.Second,at the turning period from Ordovician to Silurian,sea levels presented the cycle change of deep-shallow-deep-shallow.Due to the combination of high sea levels and a stable ocean basin in early stages,an extensive anoxic tectonic sedimentary space favorable for organic matters preservation was formed in the sea floor.Third,due to the effect of tectonic movements and sea closure,palaeo-productivity of sea areas in the southern Sichuan Basin presented a trend of being high in the early stage and low in the late stage,and the deposition rate was also low in the early stage and high in the late stage.And fourth,extensive deposition and distribution of shale rich in organic matters and silica was mainly controlled by a stable sea basin with a low subsidence rate,a relatively high sea level,semi-closed waters and low deposition rates.To sum up,the high-quality shale in the Upper Yangtze region is characterized by multiphase superimposition,lateral extension and northwestward renewal of sedimentary ages,and it is mainly deposited in Wufeng-Rhuddanian age and secondarily in Aeronian age.The main exploration layers are Wufeng-Rhuddanian in southerneeastern Sichuan Depression,Rhuddanian-Aeronian in Weiyuan area,and Wufeng-Telychian in central-northern Sichuan Basin.展开更多
Over years of oil and gas exploration in the Qaidam Basin,reservoirs have been discovered in many layers.In the Shizigou area,western Qaidam Basin,the upper member of Oligocene Lower Ganchaigou Fm is an important targ...Over years of oil and gas exploration in the Qaidam Basin,reservoirs have been discovered in many layers.In the Shizigou area,western Qaidam Basin,the upper member of Oligocene Lower Ganchaigou Fm is an important target for oil and gas exploration,and gypsum-salt rocks are the high-quality caprocks for the preservation of oil and gas reservoirs in this area.For predicting oil and gas exploration direction and target in the western Qaidam Basin and providing guidance for its oil and gas exploration deployment,its depositional characteristics and environment of gypsum-salt rocks in this area were investigated based on the core observation,thin section identification,and analysis of grain size,sensitivity parameter ratios(Sr/Cu,Fe/Mn,(Fe+Al)/(Ca+Mg),V/(V+Ni)and Pr/Ph),pyrite content and inclusions.The following characteristics are identified.First,gypsum-salt rocks are mainly distributed in the depocenter of the lake basin and their thickness decreases towards the margin of the basin.They are laterally transformed into carbonate rocks or terrigenous clastic rocks.They are areally distributed in the shape of irregular ellipse.Second,gypsum-salt rocks are vertically developed mainly in the middle and upper parts of the upper member of Lower Ganchaigou Fm and they are interbedded with carbonate rocks or terrigenous clastic rocks.Their single layer thickness changes greatly,and there are many layers with good continuity.Third,Sand Group III to Group I in the upper member of Lower Ganchaigou Fm(inter-salt)are of reductive water environment of semi-deep to deep lake facies due to their sedimentation in an arid and hot climate.It is concluded that gypsum-salt rocks of the upper member of Lower Ganchaigou Fm are distributed widely with great accumulative thickness in this area;and that they are originated from deep lake water by virtue of evaporation,concentration and crystallization in an arid and hot climate instead of by hydrothermalfluid.展开更多
The marine shale gas resource in South China is abundant,but the existing conventional methods cannot meet the needs of predicting the future production development of shale gas.With the marine shale of the Lower Silu...The marine shale gas resource in South China is abundant,but the existing conventional methods cannot meet the needs of predicting the future production development of shale gas.With the marine shale of the Lower Silurian Longmaxi Fm in this region as an example and based on its development potential,the development features of the existing shale gas resources were analyzed.It is considered that the Longmaxi shale gas accumulation zones in the Sichuan Basin and its neighboring areas contain resources of about 17.4×10^(12)m^(3)and recoverable resources of about 2.9×10^(12)m^(3).In particular,the shale gas above 3500 m underground is the main body for recent development targets,with a potential production scale about 300×10^(8)m^(3).On this basis,the development features of foreign and domestic shale gas wells were studied and the drilling workload analytical method for the prediction of shale gas production was established:(1)the initial production of a single well can be used to characterize the productivity of the shale gas well,and its test production is approximate to its initial production.Due to the similarity of decline rate among shale gas wells,the single-well estimated ultimate recovery(EUR)value of a single well can be roughly speculated from its initial production,thus the production scale of a shale gasfield can be speculated according to the analysis of drilling workload;(2)currently,the expected test production of South China marine shale gas is 17.6104 m^(3)/d,and the predicted single-well EUR value is roughly 1.5108 m^(3).It is concluded that the marine shale gas in South China represents high initial production of a single well,high declining rate,longer production cycle and the drilling workload is closely related with the production of a shale gasfield.Therefore,the analysis of drilling workload shows better applicability to the evaluation of shale gas production.Based on this method,the shale gas production of the Sichuan Basin and its neighboring area in 2020 was estimated to be about 200×10^(8)m^(3).展开更多
文摘In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.
文摘A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.
基金Project supported by National Science and Technology Major Project“Development of Large Oil,Gas and CBM Fields”(No.:2011ZX05007-002,2016ZX05007-003)PetroChina Science and Technology Project(No.2016B-0602).
文摘With the continuous deepening of natural gas exploration,the quality of discovered resources gets worse and exploration targets are getting more and more complicated,so it is necessary to develop and improve natural gas geological theories continuously in order to tap and discover more natural gas resources.Therefore,geological theories on the formation of large gas fields were studied during the 12th Five-Year Plan period and the following progresses were mainly achieved.(1)Gas generation modes were established of oil cracking and highly evolved coal-measure source rocks in different geologic conditions.(2)A model was set up for evaluating quantitatively the hydrocarbon expulsion and detainment of various source rocks with different abundance.(3)Natural gas genesis identification chart was built up with multiple parameters and indexes.(4)Two carbonate rock sedimentation patterns and two tight sandstone sedimentation patterns were established.(5)A new method was developed for evaluating caprockereservoir displacement pressure difference of immediate caprocks.(6)The hydrocarbon accumulation pattern of large gas fields was established and their main controlling factors and distribution laws were summarized.Then,the natural gas exploration theories were deepened in the following five fields and their application achievements are remarkable.First,the hydrocarbon-accumulation geological theory used for large ancient carbonate gas fields was innovatively understood to promote the discovery and confirmation of the Anyue supergiant gas field in the Sichuan Basin.Second,the hydrocarbon-accumulation geological theory suitable for large tight sandstone gas fields was developed to guide the exploration of tight sandstone gas in the Ordos and Songliao basins.Third,the hydrocarbon-accumulation theory of platform margin reefs was deepened to expand the exploration of platform margin reef gas in the Sichuan Basin.Fourth,the hydrocarbon accumulation mechanism and enrichment theory of large condensate gas reservoirs were deepened to guide the exploration of large condensate gas reservoirs in the Tarim Basin.And fifth,the exploration theory of volcanic gas reservoirs with hydrocarbon-generation fault troughs as basic units was completed to realize the strategic replacement of volcanic gas reservoir exploration.
文摘To enhance the comprehension of flow characteristics and enrich the well-test theory of slanted wells,this study established a well-test model for a slanted well in a heterogeneous multi-zonal reservoir.The model considered closed boundaries at both the top and bottom,as well as an external boundary with infinite,closed,or constant pressure on the horizontal plane.We took the bi-zonal composite model as an example to carry out concrete analysis.Various contemporary mathematical techniques,including Laplace integral transformation,separation of variables,and eigenfunction methods,were employed to solve the model.The pressure solution in real space was obtained through Duhamel's principle and Stehfest numerical inversion,then analytical curves created,and flow stages were defined for a slanted well in a bi-zonal composite reservoir.In addition,we performed a sensitivity analysis on some parameters affecting the curves.For a tri-zonal composite model,we also plotted the well-test curves and categorized them.Finally,we validated the model through the interpretation of an example well.The results show that the fluid flow of a slanted well in a bi-zonal composite reservoir can be divided into seven main stages,including wellbore storage effect(WSE)stage,skin effect(SE)stage,linear flow(LF)stage,radial flow(RF)stage of the 1st zone,transitional flow(TF)stage from the 1st to the 2nd zone,RF stage of the 2nd zone,and the external boundary response stage.The position of the pressure curve at the SE stage and LF stage decreases as the length and inclination angle increase.Correspondingly,the pressure curve at the RF stage of the 2nd zone and external boundary response stage decreases with increasing mobility ratio.Furthermore,as the radius of the 1st zone increases,the pressure curve at the RF stage of the 1st zone and the TF stage shifts towards the right.The established model and plotted curves provide a theoretical basis for further studies on the flow behavior of slanted wells in composite reservoirs.
文摘In this paper,the shale of Upper Ordovician Wufeng Fm-Lower Silurian Longmaxi Fm was taken as an example to reveal the distribution patterns and the main sedimentation controlling factors of high-quality shale in the Upper Yangtze region.This study was made from the aspects of plate movement,fluctuation of sea level,palaeo-productivity,deposition rate and paleogeographic environment,based on the field outcrop sections and drilling data of the southern Sichuan Basin,together with geochemical element testing and biostratigraphical analysis results.The following findings were obtained.First,the collision and joint of Yangtze Plate and its periphery plates and the intra-plate deformation were gentle in the early stage,strong in the late stage,gentle in northwest and strong in southeast,so the sedimentation center in the Upper Yangtze region migrated to the northwest and the closure of sea area in the southern Sichuan Basin changed from weak in early stages to strong in late stages.Second,at the turning period from Ordovician to Silurian,sea levels presented the cycle change of deep-shallow-deep-shallow.Due to the combination of high sea levels and a stable ocean basin in early stages,an extensive anoxic tectonic sedimentary space favorable for organic matters preservation was formed in the sea floor.Third,due to the effect of tectonic movements and sea closure,palaeo-productivity of sea areas in the southern Sichuan Basin presented a trend of being high in the early stage and low in the late stage,and the deposition rate was also low in the early stage and high in the late stage.And fourth,extensive deposition and distribution of shale rich in organic matters and silica was mainly controlled by a stable sea basin with a low subsidence rate,a relatively high sea level,semi-closed waters and low deposition rates.To sum up,the high-quality shale in the Upper Yangtze region is characterized by multiphase superimposition,lateral extension and northwestward renewal of sedimentary ages,and it is mainly deposited in Wufeng-Rhuddanian age and secondarily in Aeronian age.The main exploration layers are Wufeng-Rhuddanian in southerneeastern Sichuan Depression,Rhuddanian-Aeronian in Weiyuan area,and Wufeng-Telychian in central-northern Sichuan Basin.
基金Project supported by the National Science and Technology Major Project“Qaidam Basin Complex Structural Area Hydrocarbon Accumulation,Key Exploration Technology and New Field Target Optimization”(No.2016ZX05003-006)China National Petroleum Corporation Major Science and Technology special“Qaidam Basin construction of 10 million tons of oil and gas field comprehensive supporting technology research”(No.2011-ZG-001004).
文摘Over years of oil and gas exploration in the Qaidam Basin,reservoirs have been discovered in many layers.In the Shizigou area,western Qaidam Basin,the upper member of Oligocene Lower Ganchaigou Fm is an important target for oil and gas exploration,and gypsum-salt rocks are the high-quality caprocks for the preservation of oil and gas reservoirs in this area.For predicting oil and gas exploration direction and target in the western Qaidam Basin and providing guidance for its oil and gas exploration deployment,its depositional characteristics and environment of gypsum-salt rocks in this area were investigated based on the core observation,thin section identification,and analysis of grain size,sensitivity parameter ratios(Sr/Cu,Fe/Mn,(Fe+Al)/(Ca+Mg),V/(V+Ni)and Pr/Ph),pyrite content and inclusions.The following characteristics are identified.First,gypsum-salt rocks are mainly distributed in the depocenter of the lake basin and their thickness decreases towards the margin of the basin.They are laterally transformed into carbonate rocks or terrigenous clastic rocks.They are areally distributed in the shape of irregular ellipse.Second,gypsum-salt rocks are vertically developed mainly in the middle and upper parts of the upper member of Lower Ganchaigou Fm and they are interbedded with carbonate rocks or terrigenous clastic rocks.Their single layer thickness changes greatly,and there are many layers with good continuity.Third,Sand Group III to Group I in the upper member of Lower Ganchaigou Fm(inter-salt)are of reductive water environment of semi-deep to deep lake facies due to their sedimentation in an arid and hot climate.It is concluded that gypsum-salt rocks of the upper member of Lower Ganchaigou Fm are distributed widely with great accumulative thickness in this area;and that they are originated from deep lake water by virtue of evaporation,concentration and crystallization in an arid and hot climate instead of by hydrothermalfluid.
基金supported by the National Key Basic Rescarch Program of China(973 Program)(No.:2012CB214700).
文摘The marine shale gas resource in South China is abundant,but the existing conventional methods cannot meet the needs of predicting the future production development of shale gas.With the marine shale of the Lower Silurian Longmaxi Fm in this region as an example and based on its development potential,the development features of the existing shale gas resources were analyzed.It is considered that the Longmaxi shale gas accumulation zones in the Sichuan Basin and its neighboring areas contain resources of about 17.4×10^(12)m^(3)and recoverable resources of about 2.9×10^(12)m^(3).In particular,the shale gas above 3500 m underground is the main body for recent development targets,with a potential production scale about 300×10^(8)m^(3).On this basis,the development features of foreign and domestic shale gas wells were studied and the drilling workload analytical method for the prediction of shale gas production was established:(1)the initial production of a single well can be used to characterize the productivity of the shale gas well,and its test production is approximate to its initial production.Due to the similarity of decline rate among shale gas wells,the single-well estimated ultimate recovery(EUR)value of a single well can be roughly speculated from its initial production,thus the production scale of a shale gasfield can be speculated according to the analysis of drilling workload;(2)currently,the expected test production of South China marine shale gas is 17.6104 m^(3)/d,and the predicted single-well EUR value is roughly 1.5108 m^(3).It is concluded that the marine shale gas in South China represents high initial production of a single well,high declining rate,longer production cycle and the drilling workload is closely related with the production of a shale gasfield.Therefore,the analysis of drilling workload shows better applicability to the evaluation of shale gas production.Based on this method,the shale gas production of the Sichuan Basin and its neighboring area in 2020 was estimated to be about 200×10^(8)m^(3).
