四川盆地元坝中部地区须四段与珍珠冲段裂缝发育特征及发育模式OA

To explore the development characteristics,effectiveness,and main controlling factors of reservoir fractures in the 4th Member of the Upper Triassic Xujiahe Formation(Xujiahe 4 Member)and the Zhenzhuchong Member of the Lower Jurassic Ziliujing Formation in the central Yuanba area of the Sichuan Basin,a systematic investigation was carried out using drilling,core,image logging,and thin section data.The results indicate that the fractures in the Xujiahe 4 Member and Zhenzhuchong Member are dominated by low-angle and high-angle fractures,with a dominant orientation of northwest(NW)-trending,which is basically consistent with the direction of the present-day maximum horizontal principal stress.Most of the high-angle or vertical fractures in the study area are semi-filled or unfilled,exhibiting good effectiveness.Based on the analysis of burial history,homogenization temperatures of fluid inclusions,and image logging data,three stages of tectonic fractures have been identified in the study area:① During the middle-late Yanshanian movement,under nearly north-south(SN)-trending compressive stress,two sets of planar"X"-shaped shear fractures(NW-trending and northeast(NE)-trending)were formed;② During the early-middle Himalayan movement,affected by NE-trending compressive stress,planar"X"-shaped shear fractures(near SN-trending and northeast-east(NEE)-trending)were developed;③ During the late Himalayan movement,NW-trending shear fractures were formed under the continuous action of NE-trending tectonic stress.A development pattern for the formation and effectiveness of the three-stage fractures controlled by two-stage tectonic movements was established,among which the NW-trending tectonic shear fractures formed in the third stage are the most effective.Overall,multi-stage tectonic fractures are well-developed in the Xujiahe 4 Member and Zhenzhuchong Member in the central Yuanba area,and their development characteristics are jointly controlled by lithology,sandbody thickness,and faults.