Based on development practices of Gulong shale oil and a series of experiments on interactions between CO_(2) and the rocks and fluids of shale oil reservoirs, the application and adaptability of CO_(2) pre-fracturing...Based on development practices of Gulong shale oil and a series of experiments on interactions between CO_(2) and the rocks and fluids of shale oil reservoirs, the application and adaptability of CO_(2) pre-fracturing to the Gulong shale oil reservoirs are systematically evaluated. The pilot tests indicate that compared to wells with conventional fracturing, the wells with CO_(2) pre-fracturing demonstrate four significant characteristics: high but rapidly declined initial production, low cumulative production, high and unstable gas-oil ratio, and non-competitive liquid production. These characteristics are attributed to two facts. First, pre-fracturing with CO_(2) inhibits the cross-layer extension of the main fractures in the Gulong shale oil reservoirs, reduces the stimulated reservoir volume, weakens the fracture conductivity, and decreases the matrix permeability and porosity, ultimately impeding the engineering performance. Second, due to the confinement effect, pre-fracturing with CO_(2) increases the saturation pressure difference between the fracture-macropore system and the matrix micropore system, leading to continuous gas production and light hydrocarbon evaporation in the fracture-macropore system, and difficult extraction of crude oil in the matrix-micropore system, which affects the stable production. Under the superposition of various characteristics of Gulong shale oil reservoirs, pre-fracturing with CO_(2) has some negative impacts on reservoir stimulation (fracture extension and fracture conductivity), matrix seepage, and fluid phase and production, which restrict the application performance of CO_(2) pre-fracturing in the Gulong shale oil reservoirs.展开更多
A seepage-geomechanical coupled embedded fracture flow model has been established for multi-field coupled simulation in tight oil reservoirs,revealing the patterns of change in pressure field,seepage field,and stress ...A seepage-geomechanical coupled embedded fracture flow model has been established for multi-field coupled simulation in tight oil reservoirs,revealing the patterns of change in pressure field,seepage field,and stress field after long-term water injection in tight oil reservoirs.Based on this,a technique for enhanced oil recovery(EOR)combining multi-field reconstruction and combination of displacement and imbibition in tight oil reservoirs has been proposed.The study shows that after long-term water flooding for tight oil development,the pressure diffusion range is limited,making it difficult to establish an effective displacement system.The variation in geostress exhibits diversity,with the change in horizontal minimum principal stress being greater than that in horizontal maximum principal stress,and the variation around the injection wells being more significant than that around the production wells.The deflection of geostress direction around injection wells is also large.The technology for EOR through multi-field reconstruction and combination of displacement and imbibition employs water injection wells converted to production and large-scale fracturing techniques to restructure the artificial fracture network system.Through a full lifecycle energy replenishment method of pre-fracturing energy supplementation,energy increase during fracturing,well soaking for energy storage,and combination of displacement and imbibition,it effectively addresses the issue of easy channeling of the injection medium and difficult energy replenishment after large-scale fracturing.By intensifying the imbibition effect through the coordination of multiple wells,it reconstructs the combined system of displacement and imbibition under a complex fracture network,transitioning from avoiding fractures to utilizing them,thereby improving microscopic sweep and oil displacement efficiencies.Field application in Block Yuan 284 of the Huaqing Oilfield in the Ordos Basin has demonstrated that this technology increases the recovery factor by 12 percentage points,enabling large scale and efficient development of tight oil.展开更多
Based on systematically summarizing the achievements of previous ion-matched waterflooding researches,the diversity and synergy of oil recovery enhancement mechanisms and the interaction between mechanisms are examine...Based on systematically summarizing the achievements of previous ion-matched waterflooding researches,the diversity and synergy of oil recovery enhancement mechanisms and the interaction between mechanisms are examined according to two classification standards,and the influence of behaviors of different ions on different mechanisms and oil displacement efficiency are investigated.Ionic strength is proposed to characterize the behavior differences of univalent and divalent ions,the relationships between ionic strength,effective concentration,and mechanisms are established to characterize the ion behavior behind various mechanisms,and evaluate the performance of ion-matched injection water.The mechanisms of enhancing oil recovery by ion-matched waterflooding include:(1)The ion-matched water can reduce the ion strength and match the ion composition of formation water,thereby reducing the difference between the effective concentration of univalent ions and divalent ions on the surface of carbonate rocks,and improving the effective concentration of potential determining ions(especially SO42-).(2)It can improve wettability,oil-water interface properties,pore structure and physical properties of the reservoir,and finally enable the establishment of a new ionic equilibrium conducive to waterflooding while breaking the original equilibrium.In this study,experiments such as relative permeability curve,interfacial tension,and core-flooding were carried out on carbonate core samples from the Cretaceous Mishrif Formation reservoirs in Halfaya Oilfield,Middle East,a method for injection water evaluation was established and the injection water suitable for these reservoirs was selected:6 times diluted seawater.Compared with ordinary seawater,oil displacement efficiency can be increased by more than 4.60%and compared with the optimum dilution of formation water,oil displacement efficiency can be increased by 3.14%.展开更多
基金Supported by the National Natural Science Foundation of China(U22B2075)。
文摘Based on development practices of Gulong shale oil and a series of experiments on interactions between CO_(2) and the rocks and fluids of shale oil reservoirs, the application and adaptability of CO_(2) pre-fracturing to the Gulong shale oil reservoirs are systematically evaluated. The pilot tests indicate that compared to wells with conventional fracturing, the wells with CO_(2) pre-fracturing demonstrate four significant characteristics: high but rapidly declined initial production, low cumulative production, high and unstable gas-oil ratio, and non-competitive liquid production. These characteristics are attributed to two facts. First, pre-fracturing with CO_(2) inhibits the cross-layer extension of the main fractures in the Gulong shale oil reservoirs, reduces the stimulated reservoir volume, weakens the fracture conductivity, and decreases the matrix permeability and porosity, ultimately impeding the engineering performance. Second, due to the confinement effect, pre-fracturing with CO_(2) increases the saturation pressure difference between the fracture-macropore system and the matrix micropore system, leading to continuous gas production and light hydrocarbon evaporation in the fracture-macropore system, and difficult extraction of crude oil in the matrix-micropore system, which affects the stable production. Under the superposition of various characteristics of Gulong shale oil reservoirs, pre-fracturing with CO_(2) has some negative impacts on reservoir stimulation (fracture extension and fracture conductivity), matrix seepage, and fluid phase and production, which restrict the application performance of CO_(2) pre-fracturing in the Gulong shale oil reservoirs.
基金Supported by the Joint Fund Project of the National Natural Science Foundation of China(U22B2075).
文摘A seepage-geomechanical coupled embedded fracture flow model has been established for multi-field coupled simulation in tight oil reservoirs,revealing the patterns of change in pressure field,seepage field,and stress field after long-term water injection in tight oil reservoirs.Based on this,a technique for enhanced oil recovery(EOR)combining multi-field reconstruction and combination of displacement and imbibition in tight oil reservoirs has been proposed.The study shows that after long-term water flooding for tight oil development,the pressure diffusion range is limited,making it difficult to establish an effective displacement system.The variation in geostress exhibits diversity,with the change in horizontal minimum principal stress being greater than that in horizontal maximum principal stress,and the variation around the injection wells being more significant than that around the production wells.The deflection of geostress direction around injection wells is also large.The technology for EOR through multi-field reconstruction and combination of displacement and imbibition employs water injection wells converted to production and large-scale fracturing techniques to restructure the artificial fracture network system.Through a full lifecycle energy replenishment method of pre-fracturing energy supplementation,energy increase during fracturing,well soaking for energy storage,and combination of displacement and imbibition,it effectively addresses the issue of easy channeling of the injection medium and difficult energy replenishment after large-scale fracturing.By intensifying the imbibition effect through the coordination of multiple wells,it reconstructs the combined system of displacement and imbibition under a complex fracture network,transitioning from avoiding fractures to utilizing them,thereby improving microscopic sweep and oil displacement efficiencies.Field application in Block Yuan 284 of the Huaqing Oilfield in the Ordos Basin has demonstrated that this technology increases the recovery factor by 12 percentage points,enabling large scale and efficient development of tight oil.
基金Supported by the China National Science and Technology Major Project(2017ZX05030-001).
文摘Based on systematically summarizing the achievements of previous ion-matched waterflooding researches,the diversity and synergy of oil recovery enhancement mechanisms and the interaction between mechanisms are examined according to two classification standards,and the influence of behaviors of different ions on different mechanisms and oil displacement efficiency are investigated.Ionic strength is proposed to characterize the behavior differences of univalent and divalent ions,the relationships between ionic strength,effective concentration,and mechanisms are established to characterize the ion behavior behind various mechanisms,and evaluate the performance of ion-matched injection water.The mechanisms of enhancing oil recovery by ion-matched waterflooding include:(1)The ion-matched water can reduce the ion strength and match the ion composition of formation water,thereby reducing the difference between the effective concentration of univalent ions and divalent ions on the surface of carbonate rocks,and improving the effective concentration of potential determining ions(especially SO42-).(2)It can improve wettability,oil-water interface properties,pore structure and physical properties of the reservoir,and finally enable the establishment of a new ionic equilibrium conducive to waterflooding while breaking the original equilibrium.In this study,experiments such as relative permeability curve,interfacial tension,and core-flooding were carried out on carbonate core samples from the Cretaceous Mishrif Formation reservoirs in Halfaya Oilfield,Middle East,a method for injection water evaluation was established and the injection water suitable for these reservoirs was selected:6 times diluted seawater.Compared with ordinary seawater,oil displacement efficiency can be increased by more than 4.60%and compared with the optimum dilution of formation water,oil displacement efficiency can be increased by 3.14%.
