This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke cu...This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny(Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55-94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170-196 m and 11 298 km^(2), respectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle-Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma 4 Member-pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.展开更多
This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation)...This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.展开更多
1 Introduction Shale formations bear abundant mineral resource and*unconventional petroleum resource,and the unconventional petroleum resource that contain in the shale formation should be integrated and researched.
To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies, we investigate two dolomite reservoir types, i.e. wea...To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies, we investigate two dolomite reservoir types, i.e. weathering-crust karstic reservoirs and mound-beach reservoirs, in the Ordovician Majiagou Formation, Ordos Basin by using in-situ laser ablation U-Pb dating as well as carbon and oxygen isotopic composition analysis. The results show that:(1) According to the dating of 8 reservoir samples, the Majiagou Formation experienced 5 diagenetic stages(Stage 1: deposition of matrix dolomite or penecontemporaneous dolomitization, in 444.0–494.0 Ma;Stage 2: dogtooth-or blade-shaped dolomite cementation, in 440.0–467.0 Ma;Stage 3: dolomitic silt filling, in 316.5–381.0 Ma;Stage 4: crystalline dolomite filling, in 354.0 Ma;Stage 5: crystalline calcite filling, in 292.7–319.0 Ma).(2) Supra-salt weathering-crust karstic dolomite reservoirs went through several diagenetic processes including penecontemporaneous dolomitization, compaction, weathering-crust karstification, packing, and rupturing in succession. Gypsum mold pores formed in the phase of hypergenic karstification and were filled with such minerals as dolomitic silts and calcites, and thus the porosity decreased from 10%–40% to 3%–8%.(3) Sub-salt mound-beach dolomite reservoirs went through the diagenetic processes including penecontemporaneous dolomitization, compaction, subsea cementation, penecontemporaneous corrosion, infiltration backflow dolomitization, packing, and rupturing. The porosity of reservoirs was originally 10%–30%, decreased to 0–6% due to seawater cementation, rose back to 5%–15% owing to penecontemporaneous corrosion, and finally declined to 2%–6% as a result of crystalline dolomites and calcites packing. The above methodology for the restoration of dolomitization and porosity evolution may be helpful for the restoration of porosity evolution in other basins or series of strata.展开更多
After 50 years of oil and gas exploration in Longdong area of southwest Ordos Basin,NW China,a deep coal-formed gas field was discovered for the first time in Qingyang area.Through observation of field outcrops and co...After 50 years of oil and gas exploration in Longdong area of southwest Ordos Basin,NW China,a deep coal-formed gas field was discovered for the first time in Qingyang area.Through observation of field outcrops and core,analysis of common,cast and cathode thin sections,Ro and other geochemistry indexes,carbon isotope,electron microscope and other supporting tests and analyses,the hydrocarbon generation,reserves formation and reservoir formation characteristics of gas reservoirs at different buried depths in Yishaan slope were examined and compared.The deep gas reservoir has an average buried depth of more than 4200 m,and the main gas-bearing formation is the Member 1 of Lower Permian Shanxi Formation,which is characterized by low porosity,low permeability,low pressure and low abundance.It is believed that hydrocarbon generation in thin seam coal source rocks with high thermal evolution can form large gas fields,high-quality sandstone reservoirs with dissolved pores,intergranular pores and intercrystalline pores can still develop in late diagenetic stage under deep burial depth and high thermal evolution,and fractures improve the permeability of reservoirs.High drying coefficient of natural gas and negative carbon isotope series are typical geochemical characteristics of deep coal-formed gas.The integrated exploration and development method has been innovated,and the economic and effective development mode of gas fields of"dissecting sand body by framework vertical wells,centralized development by horizontal wells"has been formed.The discovery and successful exploration of the large gas field has provided geological basis and technical support for the construction of natural gas fields of 100 billion cubic meter scale in the southwest of the basin,and has important guidance for exploration of coal-derived gas with deep buried depth and high thermal evolution widely distributed in China.展开更多
Efficient large-scale development of ultra-low-permeability reservoirs(0.3-1 mD)has been achieved in the Changqing Oilfield,Ordos Basin of China.According to unique features of petroleum exploration and development in...Efficient large-scale development of ultra-low-permeability reservoirs(0.3-1 mD)has been achieved in the Changqing Oilfield,Ordos Basin of China.According to unique features of petroleum exploration and development in this basin,tight oil herein refers to petroleum that occurs in oil-bearing shales and interbedded tight sandstone reservoirs adjacent to source rocks with ambient air permeability<0.3 mD.Tight oil in tight sandstone and shale have generally not yet experienced large-scale long-distance migration.In the Yanchang Formation,tight oil has mainly accumulated in the semi-deep to deep lacustrine facies,typically in oil-bearing shales and tight sandstones of the 7th member oil-bearing formation and tight sandstones of the 6th member oil-bearing formation in the center of the basin.Tight oil resource in the Ordos Basin is characterized by wide spatial distribution,excellent source rocks,extremely tight sandstone reservoirs,complex pore throat structures,poor physical properties,high oil saturation,good crude-oil properties,and low reservoir pressure.A fundamental feature of the continuous oil and gas accumulation in tight oil reservoirs is the widespread development of nano-scale pore-throat systems.In the Yanchang Formation,most of connected pore throats in tight sandstone reservoirs have diameters greater than critical pore throat diameter,allowing oil and gas migration in the tight reservoirs.According to contact relationship between tight reservoirs and source rocks,three types of tight oil reservoirs are identified in the Yanchang Formation,i.e.,tight massive sandstone reservoir,sand-shale interbed reservoir,and oil-bearing shale reservoir.In the Ordos Basin,tight oil is widely distributed in the 6th and 7th members of the Yanchang Formation,with total resources estimated to be 3×10^(9) t.These include>1×10^(9) t of oil resources in shale in the 7th member of the Yanchang Formation and approximately 0.9×10^(9) t and 1.1×10^(9) t of tight sandstone oil resource in the 6th and 7th members of the Yanchang Formation,respectively.These tight oil resources are the realistic resources addition for the oilfield,which can ensure an annual production of 50×10^(6) t of oil and gas equivalent and maintain long-term stable oil production in the Changqing Oilfield,Ordos Basin,China.展开更多
基金Supported by the Major Science and Technology Project of PetroChina Changqing Oilfield Company (ZDZX2021-01)。
文摘This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny(Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55-94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170-196 m and 11 298 km^(2), respectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle-Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma 4 Member-pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.
基金financially supported by the National Natural Science Foundation of China (grant No.41502147)Sichuan Province University Scientific Innovation Team Construction Project (USITCP)+1 种基金the Yong Scholars Development Fund of SWPU (grant No.201499010089)the National Science and Technology Major Project (grant No.2011ZX05001-001-04)
文摘This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.
基金supported by funding the National Basic Research Program of China (973 Program) and the grant number is 2014CB239000
文摘1 Introduction Shale formations bear abundant mineral resource and*unconventional petroleum resource,and the unconventional petroleum resource that contain in the shale formation should be integrated and researched.
基金Supported by the National Science and Technology Major Project of China (2016ZX05004-002)PetroChina Science and Technology Project (2016E-05-142021DJ0503)。
文摘To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies, we investigate two dolomite reservoir types, i.e. weathering-crust karstic reservoirs and mound-beach reservoirs, in the Ordovician Majiagou Formation, Ordos Basin by using in-situ laser ablation U-Pb dating as well as carbon and oxygen isotopic composition analysis. The results show that:(1) According to the dating of 8 reservoir samples, the Majiagou Formation experienced 5 diagenetic stages(Stage 1: deposition of matrix dolomite or penecontemporaneous dolomitization, in 444.0–494.0 Ma;Stage 2: dogtooth-or blade-shaped dolomite cementation, in 440.0–467.0 Ma;Stage 3: dolomitic silt filling, in 316.5–381.0 Ma;Stage 4: crystalline dolomite filling, in 354.0 Ma;Stage 5: crystalline calcite filling, in 292.7–319.0 Ma).(2) Supra-salt weathering-crust karstic dolomite reservoirs went through several diagenetic processes including penecontemporaneous dolomitization, compaction, weathering-crust karstification, packing, and rupturing in succession. Gypsum mold pores formed in the phase of hypergenic karstification and were filled with such minerals as dolomitic silts and calcites, and thus the porosity decreased from 10%–40% to 3%–8%.(3) Sub-salt mound-beach dolomite reservoirs went through the diagenetic processes including penecontemporaneous dolomitization, compaction, subsea cementation, penecontemporaneous corrosion, infiltration backflow dolomitization, packing, and rupturing. The porosity of reservoirs was originally 10%–30%, decreased to 0–6% due to seawater cementation, rose back to 5%–15% owing to penecontemporaneous corrosion, and finally declined to 2%–6% as a result of crystalline dolomites and calcites packing. The above methodology for the restoration of dolomitization and porosity evolution may be helpful for the restoration of porosity evolution in other basins or series of strata.
基金Supported by the National Key Basic Research and Development Program(973 Program),China(2014CB239003)China National Science and Technology Major Project(2016ZX05050,2017ZX05001002).
文摘After 50 years of oil and gas exploration in Longdong area of southwest Ordos Basin,NW China,a deep coal-formed gas field was discovered for the first time in Qingyang area.Through observation of field outcrops and core,analysis of common,cast and cathode thin sections,Ro and other geochemistry indexes,carbon isotope,electron microscope and other supporting tests and analyses,the hydrocarbon generation,reserves formation and reservoir formation characteristics of gas reservoirs at different buried depths in Yishaan slope were examined and compared.The deep gas reservoir has an average buried depth of more than 4200 m,and the main gas-bearing formation is the Member 1 of Lower Permian Shanxi Formation,which is characterized by low porosity,low permeability,low pressure and low abundance.It is believed that hydrocarbon generation in thin seam coal source rocks with high thermal evolution can form large gas fields,high-quality sandstone reservoirs with dissolved pores,intergranular pores and intercrystalline pores can still develop in late diagenetic stage under deep burial depth and high thermal evolution,and fractures improve the permeability of reservoirs.High drying coefficient of natural gas and negative carbon isotope series are typical geochemical characteristics of deep coal-formed gas.The integrated exploration and development method has been innovated,and the economic and effective development mode of gas fields of"dissecting sand body by framework vertical wells,centralized development by horizontal wells"has been formed.The discovery and successful exploration of the large gas field has provided geological basis and technical support for the construction of natural gas fields of 100 billion cubic meter scale in the southwest of the basin,and has important guidance for exploration of coal-derived gas with deep buried depth and high thermal evolution widely distributed in China.
基金This work was suppor ted by National Science and Technology Major Project of China(Grant No.2011ZX05044,2011ZX05001)National Key Basic Research Program(973 Program)of China(2014CB239003).
文摘Efficient large-scale development of ultra-low-permeability reservoirs(0.3-1 mD)has been achieved in the Changqing Oilfield,Ordos Basin of China.According to unique features of petroleum exploration and development in this basin,tight oil herein refers to petroleum that occurs in oil-bearing shales and interbedded tight sandstone reservoirs adjacent to source rocks with ambient air permeability<0.3 mD.Tight oil in tight sandstone and shale have generally not yet experienced large-scale long-distance migration.In the Yanchang Formation,tight oil has mainly accumulated in the semi-deep to deep lacustrine facies,typically in oil-bearing shales and tight sandstones of the 7th member oil-bearing formation and tight sandstones of the 6th member oil-bearing formation in the center of the basin.Tight oil resource in the Ordos Basin is characterized by wide spatial distribution,excellent source rocks,extremely tight sandstone reservoirs,complex pore throat structures,poor physical properties,high oil saturation,good crude-oil properties,and low reservoir pressure.A fundamental feature of the continuous oil and gas accumulation in tight oil reservoirs is the widespread development of nano-scale pore-throat systems.In the Yanchang Formation,most of connected pore throats in tight sandstone reservoirs have diameters greater than critical pore throat diameter,allowing oil and gas migration in the tight reservoirs.According to contact relationship between tight reservoirs and source rocks,three types of tight oil reservoirs are identified in the Yanchang Formation,i.e.,tight massive sandstone reservoir,sand-shale interbed reservoir,and oil-bearing shale reservoir.In the Ordos Basin,tight oil is widely distributed in the 6th and 7th members of the Yanchang Formation,with total resources estimated to be 3×10^(9) t.These include>1×10^(9) t of oil resources in shale in the 7th member of the Yanchang Formation and approximately 0.9×10^(9) t and 1.1×10^(9) t of tight sandstone oil resource in the 6th and 7th members of the Yanchang Formation,respectively.These tight oil resources are the realistic resources addition for the oilfield,which can ensure an annual production of 50×10^(6) t of oil and gas equivalent and maintain long-term stable oil production in the Changqing Oilfield,Ordos Basin,China.