Influence mechanisms of pressure difference in fracture ends on dynamic imbibition and displacement in shale reservoirs
The pressure difference between the pressure exerted by fracturing fluid and the pressure of reservoir matrix at the ends of the fractures can have an important influence on oil-water imbibition and displacement.In this study,using cores col-lected from Chang 7 shale formation,simulation experiments of imbibition and displacement under different fracture end pres-sure difference were carried out under conditions of supplement formation energy with high pressure injection of fracturing flu-id and well shut-in with constant pressure.In the experiments,a dynamic nuclear magnetic resonance(NMR)technique,real-time pressure detection,and visual image analysis were applied to analyze and interpret the influence mechanisms of the fracture end pressure difference.The results show that reverse differential pressure with reverse imbibition can be obviously observed,especially in the process of supplement formation energy by the fracturing fluid,in which,with the increase of the fracture end pressure difference,the efficiency of imbibition and displacement gradually increases.The efficiency of imbibi-tion and displacement is dominated in the micro pores(at 0-6 MPa,the imbibition and displacement efficiency are 33.31%,29.51%,35.65%and 64.89%respectively).In the process of well shut-in with a constant pressure,the reverse differential pressure imbibition is reduced due to the weakening of the differential pressure in micro pores,and the imbibition and displacement process are still dominated by reverse imbibition with capillary force,while oil in large pores can imbibe in-to micro pores.
fracture end pressure differenceshale oil reservoirdynamic imbibitionnuclear magnetic resonance
何延龙、黄海、唐梅荣、倪军、李华周、TAYFUN Babadagli、张轩诚
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西安石油大学石油工程学院,陕西西安 710065
西部低渗-特低渗透油藏开发与治理教育部工程研究中心,陕西西安 710065
中国石油长庆油田分公司天然气评价项目部,陕西西安 710065
延长石油(集团)有限责任公司,陕西西安 710065
School of Mining and Petroleum Engineering,Faculty of Engineering,University of Alberta,Edmonton T6G1H9
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