The third member of Shahejie Formation(also referred to as Sha 3 Member)in Dongpu Depression,China,a volatile,low-permeability oil reservoir with complex fluid compositions,is subjected to high temperature and high pr...The third member of Shahejie Formation(also referred to as Sha 3 Member)in Dongpu Depression,China,a volatile,low-permeability oil reservoir with complex fluid compositions,is subjected to high temperature and high pressure(HPHT),which poses significant challenges to conventional water injection.To elucidate flow mechanisms and optimize development strategies,this study integrates constant-rate mercury injection(CRMI),nuclear magnetic resonance(NMR),and HPHT three-phase oil/gas/water relative permeability experiments to analyze pore-throat structures,movable fluid characteristics,and relative permeability.The CRMI results indicate that the reservoir exhibits low porosity and low permeability,with dominant throat radius ranging from 0.6 to 5.0μm,and mean pore-throat radius ratio ranging from 40.303 to 278.320,demonstrating significant microscopic heterogeneity.The NMR results reveal that water-alternating-gas(WAG)injection enhances oil recovery by 16.28%(Sample W1)and 13.52%(Sample W2)compared to conventional water injection,primarily due to the gas phase's low viscosity and high mobility,enabling access to micropores unreachable by water phases.The HPHT three-phase relative permeability tests demonstrate positive correlations between saturation and relative permeability,with oil permeability significantly influenced by three-phase saturation and rock wettability.These findings establish a microscopic seepage model for optimizing enhanced oil recovery(EOR)strategies in volatile reservoirs.展开更多
The BZ oilfield in the Bohai Sea is a rare,highly volatile reservoir with fractures in the metamorphic rocks of buried hills.Clarifying the mechanism of gas injection for improving oil recovery and determining the opt...The BZ oilfield in the Bohai Sea is a rare,highly volatile reservoir with fractures in the metamorphic rocks of buried hills.Clarifying the mechanism of gas injection for improving oil recovery and determining the optimal way to deploy injection-production well networks are critical issues that must be urgently addressed for efficient oilfield development.Experimental research on the mixed-phase displacement mechanism through gas injection into indoor formation fluids was conducted to guide the efficient development of gas injection in oil fields.We established a model of dual-medium reservoir composition and researched the deployment strategy for a three-dimensional well network for gas injection development.The coupling relationship between key influencing factors of the well network and fracture development was also quantitatively analyzed.The results show that the solubility of the associated gas and strong volatile oil system injected into the BZ oilfield is high.This high solubility demonstrates a mixed-phase displacement mechanism involving intermediate hydrocarbons,dissolution and condensation of medium components,and coexistence of extraction processes.Injecting gas and crude oil can achieve a favorable mixing effect when the local formation pressure is greater than 35.79 MPa.Associated gas reinjection is recommended to supplement energy for developing the highly volatile oil reservoirs in the fractured buried hills of the BZ oilfield.This recommendation involves fully utilizing the structural position and gravity-assisted oil displacement mechanism to deploy an injection-production well network.Gas injection points should be constructed at the top of high areas,and oil production points should be placed at the middle and lower parts of low areas.This approach forms a spatial threedimensional well network.By adopting high inclination well development,the oil production well forms a 45°angle with the fracture direction,which increases the drainage area and enhances single-well production capacity.The optimal injection-production well spacing along the fracture direction is approximately 1000 m,while the reasonable well spacing in the vertical fracture direction is approximately 800 m.The research results were applied to the development practice of the buried hills in the BZ oilfield,which achieved favorable development results.These outcomes provide a valuable reference for the formulation of development plans and efficient gas injection development in similar oil and gas fields in buried hills.展开更多
To describe the complex phase transformation in the process of depletion exploitation of volatile oil reservoir,four fluid phases are defined,and production and remaining volume of these phases are calculated based on...To describe the complex phase transformation in the process of depletion exploitation of volatile oil reservoir,four fluid phases are defined,and production and remaining volume of these phases are calculated based on the principle of surface volume balance,then the recovery prediction method of volatile oil reservoir considering the influence of condensate content in released solution gas and the correction method of multiple degassing experiments data are established.Taking three typical kinds of crude oil(black oil,medium-weak volatile oil,strong volatile oil)as examples,the new improved method is used to simulate constant volume depletion experiments based on the corrected data of multiple degassing experiment to verify the reliability of the modified method.By using"experimental data and traditional method","corrected data and traditional method"and"corrected data and modified method",recovery factors of these three typical kinds of oil are calculated respectively.The source of parameters and the calculation methods have little effect on the recovery of typical black oil.However,with the increase of crude oil volatility,the oil recovery will be seriously underestimated by using experimental data or traditional method.The combination of"corrected data and modified method"considers the influence of condensate in gas phase in both experimental parameters and calculation method,and has good applicability to typical black oil and volatile oil.The strong shrinkage of volatile oil makes more"liquid oil"convert to"gaseous oil",so volatile oil reservoir can reach very high oil recovery by depletion drive.展开更多
A</span><span style="font-family:Verdana;">s a typical volatile oil reservoir, the actual production characteristics o</span><span style="font-family:Verdana;">f Wenchang 8-...A</span><span style="font-family:Verdana;">s a typical volatile oil reservoir, the actual production characteristics o</span><span style="font-family:Verdana;">f Wenchang 8-3 reservoir are inconsistent with the results of traditional phase equilibrium experiments. The conventional isothermal instantaneous phase equilibrium theory cannot meet the production performance or numerical simulation analysis requirements of this type of reservoir. The thermodynamic properties of volatile oil reservoirs are like those of condensate gas reservoirs. As the formation pressure drops below the dew point pressure during the mining process, the balance between the liquid phase and the gas phase is not completed instantaneously. Based on the non-equilibrium phase recovery treatment method of the condensate gas reservoir, the phase behavior change curve of the A4h well of Wenchang 8-3 oil reservoir recovered from the saturation pressure to three different pressures is analyzed. The accuracy of the numerical simulation results with or without non-equilibrium phase transition is compared. The results show that the non-equilibrium phase change has a great impact on the production performance of volatile oil reservoirs;t</span><span style="font-family:Verdana;">he numerical simulation results considering the non-equilibrium phas</span><span style="font-family:Verdana;">e transition are in good agreement with the actual production performance of a single well and can better reflect the actual situation of this type of reservoir. Therefore, considering the effects of non-equilibrium phase transitions has important guiding significance for the dynamic analysis of volatile oil reservoirs, numerical simulation, and the formulation of development management strategies.展开更多
BZ13-2 oil field is a deep submerged strongly volatile reservoir in Bohai Sea. This oil reservoir has the characteristics of high gas oil ratio and small difference in formation pressure and saturation point pressure....BZ13-2 oil field is a deep submerged strongly volatile reservoir in Bohai Sea. This oil reservoir has the characteristics of high gas oil ratio and small difference in formation pressure and saturation point pressure. It usually adopts gas injection development to avoid crude oil degassing and fast decreasing production capacity. However, the phase characteristics and miscibility mechanism of this high-temperature and high-pressure fluid after gas injection are not clear. Therefore, it is necessary to study the feasibility of CO<sub>2</sub> injection to improve oil recovery in near critical volatile oil reservoirs through CO<sub>2</sub> injection experiments. In the early stage of the depletion experiment, the content of heavy components in the remaining oil increased significantly, so the depletion method is not conducive to the development of such reservoirs. With the increase of CO<sub>2</sub> injection, the volumetric expansion coefficient of formation crude oil increases significantly, while the saturation pressure and formation crude oil viscosity remain basically unchanged. The minimum miscible pressure experiment shows that CO<sub>2</sub> injection under formation pressure conditions can achieve multiphase miscibility. Based on experimental research results, the BZ13-2 oilfield is suitable for early gas injection development and can significantly improve recovery.展开更多
基金supported by the Key R&D Plan of Shaanxi Province[key industrial innovation chain(Group)](No.2022ZDLSF07-04).
文摘The third member of Shahejie Formation(also referred to as Sha 3 Member)in Dongpu Depression,China,a volatile,low-permeability oil reservoir with complex fluid compositions,is subjected to high temperature and high pressure(HPHT),which poses significant challenges to conventional water injection.To elucidate flow mechanisms and optimize development strategies,this study integrates constant-rate mercury injection(CRMI),nuclear magnetic resonance(NMR),and HPHT three-phase oil/gas/water relative permeability experiments to analyze pore-throat structures,movable fluid characteristics,and relative permeability.The CRMI results indicate that the reservoir exhibits low porosity and low permeability,with dominant throat radius ranging from 0.6 to 5.0μm,and mean pore-throat radius ratio ranging from 40.303 to 278.320,demonstrating significant microscopic heterogeneity.The NMR results reveal that water-alternating-gas(WAG)injection enhances oil recovery by 16.28%(Sample W1)and 13.52%(Sample W2)compared to conventional water injection,primarily due to the gas phase's low viscosity and high mobility,enabling access to micropores unreachable by water phases.The HPHT three-phase relative permeability tests demonstrate positive correlations between saturation and relative permeability,with oil permeability significantly influenced by three-phase saturation and rock wettability.These findings establish a microscopic seepage model for optimizing enhanced oil recovery(EOR)strategies in volatile reservoirs.
文摘The BZ oilfield in the Bohai Sea is a rare,highly volatile reservoir with fractures in the metamorphic rocks of buried hills.Clarifying the mechanism of gas injection for improving oil recovery and determining the optimal way to deploy injection-production well networks are critical issues that must be urgently addressed for efficient oilfield development.Experimental research on the mixed-phase displacement mechanism through gas injection into indoor formation fluids was conducted to guide the efficient development of gas injection in oil fields.We established a model of dual-medium reservoir composition and researched the deployment strategy for a three-dimensional well network for gas injection development.The coupling relationship between key influencing factors of the well network and fracture development was also quantitatively analyzed.The results show that the solubility of the associated gas and strong volatile oil system injected into the BZ oilfield is high.This high solubility demonstrates a mixed-phase displacement mechanism involving intermediate hydrocarbons,dissolution and condensation of medium components,and coexistence of extraction processes.Injecting gas and crude oil can achieve a favorable mixing effect when the local formation pressure is greater than 35.79 MPa.Associated gas reinjection is recommended to supplement energy for developing the highly volatile oil reservoirs in the fractured buried hills of the BZ oilfield.This recommendation involves fully utilizing the structural position and gravity-assisted oil displacement mechanism to deploy an injection-production well network.Gas injection points should be constructed at the top of high areas,and oil production points should be placed at the middle and lower parts of low areas.This approach forms a spatial threedimensional well network.By adopting high inclination well development,the oil production well forms a 45°angle with the fracture direction,which increases the drainage area and enhances single-well production capacity.The optimal injection-production well spacing along the fracture direction is approximately 1000 m,while the reasonable well spacing in the vertical fracture direction is approximately 800 m.The research results were applied to the development practice of the buried hills in the BZ oilfield,which achieved favorable development results.These outcomes provide a valuable reference for the formulation of development plans and efficient gas injection development in similar oil and gas fields in buried hills.
基金Supported by the China National Science and Technology Major Project(2016ZX05027)。
文摘To describe the complex phase transformation in the process of depletion exploitation of volatile oil reservoir,four fluid phases are defined,and production and remaining volume of these phases are calculated based on the principle of surface volume balance,then the recovery prediction method of volatile oil reservoir considering the influence of condensate content in released solution gas and the correction method of multiple degassing experiments data are established.Taking three typical kinds of crude oil(black oil,medium-weak volatile oil,strong volatile oil)as examples,the new improved method is used to simulate constant volume depletion experiments based on the corrected data of multiple degassing experiment to verify the reliability of the modified method.By using"experimental data and traditional method","corrected data and traditional method"and"corrected data and modified method",recovery factors of these three typical kinds of oil are calculated respectively.The source of parameters and the calculation methods have little effect on the recovery of typical black oil.However,with the increase of crude oil volatility,the oil recovery will be seriously underestimated by using experimental data or traditional method.The combination of"corrected data and modified method"considers the influence of condensate in gas phase in both experimental parameters and calculation method,and has good applicability to typical black oil and volatile oil.The strong shrinkage of volatile oil makes more"liquid oil"convert to"gaseous oil",so volatile oil reservoir can reach very high oil recovery by depletion drive.
文摘A</span><span style="font-family:Verdana;">s a typical volatile oil reservoir, the actual production characteristics o</span><span style="font-family:Verdana;">f Wenchang 8-3 reservoir are inconsistent with the results of traditional phase equilibrium experiments. The conventional isothermal instantaneous phase equilibrium theory cannot meet the production performance or numerical simulation analysis requirements of this type of reservoir. The thermodynamic properties of volatile oil reservoirs are like those of condensate gas reservoirs. As the formation pressure drops below the dew point pressure during the mining process, the balance between the liquid phase and the gas phase is not completed instantaneously. Based on the non-equilibrium phase recovery treatment method of the condensate gas reservoir, the phase behavior change curve of the A4h well of Wenchang 8-3 oil reservoir recovered from the saturation pressure to three different pressures is analyzed. The accuracy of the numerical simulation results with or without non-equilibrium phase transition is compared. The results show that the non-equilibrium phase change has a great impact on the production performance of volatile oil reservoirs;t</span><span style="font-family:Verdana;">he numerical simulation results considering the non-equilibrium phas</span><span style="font-family:Verdana;">e transition are in good agreement with the actual production performance of a single well and can better reflect the actual situation of this type of reservoir. Therefore, considering the effects of non-equilibrium phase transitions has important guiding significance for the dynamic analysis of volatile oil reservoirs, numerical simulation, and the formulation of development management strategies.
文摘BZ13-2 oil field is a deep submerged strongly volatile reservoir in Bohai Sea. This oil reservoir has the characteristics of high gas oil ratio and small difference in formation pressure and saturation point pressure. It usually adopts gas injection development to avoid crude oil degassing and fast decreasing production capacity. However, the phase characteristics and miscibility mechanism of this high-temperature and high-pressure fluid after gas injection are not clear. Therefore, it is necessary to study the feasibility of CO<sub>2</sub> injection to improve oil recovery in near critical volatile oil reservoirs through CO<sub>2</sub> injection experiments. In the early stage of the depletion experiment, the content of heavy components in the remaining oil increased significantly, so the depletion method is not conducive to the development of such reservoirs. With the increase of CO<sub>2</sub> injection, the volumetric expansion coefficient of formation crude oil increases significantly, while the saturation pressure and formation crude oil viscosity remain basically unchanged. The minimum miscible pressure experiment shows that CO<sub>2</sub> injection under formation pressure conditions can achieve multiphase miscibility. Based on experimental research results, the BZ13-2 oilfield is suitable for early gas injection development and can significantly improve recovery.
