中文摘要：

以鄂尔多斯盆地安塞油田王窑区长6油层为例，利用相似露头、岩心及测井资料，在评价天然裂缝发育特征的基础上，求取了不同组系裂缝开启压力及地层破裂压力，分析影响裂缝开启压力的各种因素，进而探讨如何合理确定低渗透油藏注水压力界限。安塞油田王窑区长6油层以发育高角度构造裂缝为主，其主要方位依次为NEE－SWW、近E－W、近S－N和NW－SE向，不同组系裂缝开启压力差异较大，主要受埋藏深度、裂缝产状、孔隙流体压力及现今地应力等因素影响。合理注水压力的确定要根据各井组天然裂缝发育情况。在不发育天然裂缝的井组，注水压力不应大于地层破裂压力，避免地层发生大规模破裂而形成裂缝型水窜通道；对于发育天然裂缝的井组，若裂缝开启压力小于地层破裂压力，合理注水压力界限不应大于裂缝开启压力，以防止裂缝大规模开启和延伸；若裂缝开启压力大于地层破裂压力，则要以地层破裂压力厘定合理注水压力，以防止地层发生新的大规模破裂。

英文摘要：

Analog outcrop,core and well logging data are integrated in this paper to calculate opening pressure of fractures and formation fracture pressure in different reservoir intervals and analyzed various factors affecting opening pressure of fractures based on evaluation of natural fracture characteristics.A sensitivity analysis was performed to determine proper injection pressure for low-permeability reservoirs.High dip-angle fractures are predominant in Chang-6 reservoir in Wangyao block in Ansai oilfield,and their main orientations are NEE-SWW,E-W,S-N and NW-SE,respectively. The opening pressures vary significantly in different reservoir intervals due to the control of buried depth,fracture orienta-tion,pore fluid pressure and current geo-stress.The reasonable injection pressure should be determined by the maturity of local natural fractures accordingly.In areas with few natural fractures,water injection pressure should not be larger than formation fracture pressure,so as to avoid large-scale fracturing that leads to water breakthough.In areas with dense fractures,if the fracture opening pressure is less than the formation fracture pressure,the rational injection pressure should be set less than the formation fracture pressure to avoid large-scale opening and connection of natural fractures;otherwise the injection pressure should be properly set according to the formation fracture pressure to avoid new large-scale fracturing.