页岩油藏多重孔隙介质耦合流动数值模拟

Numerical simulation of shale oil coupled flow in multi-pore media

页岩孔隙类型多样,微纳米尺度孔隙发育,借助分段压裂水平井技术能够实商业化开采。原油分子与孔隙壁面作用较甲烷分子更加复杂,目前页岩油在无机和有机纳米孔中的运移机制尚不清楚。准确模拟页岩油微观运移机制和多重孔隙介质间耦合流动对页岩油藏产能评价和生产预测具有重要意义。结合润湿特性,考虑液体吸附、速度滑移及物性变化等机制,引入复杂结构参数(迂曲度、孔隙度和有机孔含量),建立了微纳米多孔介质液体表观渗透率模型,研究了不同运移机制对微纳米多孔介质表观渗透率影响。在此基础上,建立了基质-天然裂缝-人工裂缝耦合的页岩油藏分段压裂水平井数学模型,利用有限元方法求解,进行产能影响因素分析。结果表明,孔隙半径小于10 nm时,微纳米孔隙速度滑移影响明显,而孔隙半径大于100 nm时,微观运移机制作用可以忽略;有机孔隙含量越小、裂缝条数越多则分段压裂水平井产能越大;最优的缝网模式为缝网无间距且不重叠。本研究的重点是丰富微纳米孔隙内油气运移理论,为页岩油藏开发模拟研究提供理论方法。

Shale reservoirs are characterized by various pores with micro- and nano-pores well developed.Commercial shale oil development can be achieved by means of staged fracturing in horizontal wells.The interaction between oil molecules and pore wall is more complex than that between methane molecules and pore wall,but it is still unclear about the migration mechanism of shale oil in inorganic and organic nano-pores at present.Accurate simulation of the microscopic migration mechanisms of shale oil and the coupled flow in multi-pore media is of great significance to productivity evaluation and production prediction in shale oil reservoirs.Considering wettability and mechanisms of liquid adsorption,velocity slip and physical property change,we established the apparent permeability model for fluids in micro- and nano-scale multi-pore media based on the complex structural parameters (including tortuosity,porosity and organic pore content),to explore the effects of different migration mechanisms on the apparent permeability of micro- and nano-scale multi-pore media.Subsequently,the mathematical model with matrix,natural fracture and artificial fracture coupled was set up for multistage fractured horizontal wells in shale oil reservoirs.Besides,the finite element method was used to solve the mo- del ,and to analyze the factors affecting productivity.The results show that when the pore radius is less than 10 nm,the effect of velocity slip in micro- and nano-pores is significant,while when the pore radius is greater than 100 nm,the effect of microscopic migration mechanisms may be neglected.The less the number of organic pores and the more the number of fractures,the greater the productivity of multistage fractured horizontal wells will be.The optimal fracture network is that has neither spacing nor overlapping between the adjacent fractures.The highlight of the study is to enrich the theories on oil and gas migration in micro- and nano-pores,so as to contribute to the development simulation of shale reservoirs with theoretical methods.