水平井压裂微地震监测成果的不对称性分析

为了分析水平井压裂微地震监测成果的不对称性，为客观评价压裂效果提供依据，文中综合应用微地震监测、三维地震、录井以及压裂数据，紧密结合精细地质研究、工程设计，系统分析了54口水平井压裂的微地震监测成果，总结了导致水平井压裂微地震监测成果不对称的因素，取得如下认识：(1)导致水平井压裂微地震监测成果不对称的因素主要包括工程因素、地质因素以及完钻井分布等三个方面，其中地质因素具体包括天然裂缝、断层、岩性变化、地应力等；(2)天然裂缝、缝长距离内的完钻井会诱导压裂裂缝转向，并沿着裂缝集中发育区和完钻井周围延伸，在水平井两侧形成不对称的微地震事件分布；(3)断层对压裂裂缝具有诱导和屏蔽作用，压裂裂缝沿着断面延伸，微地震监测事件呈面状分布，压裂裂缝无法延伸至断层另一侧，形成远离水平井的单侧分布；(4)纵向隔夹层、横向的岩性变化会对压裂裂缝的延伸起控制和封隔作用，在很大程度上抑制了压裂裂缝延伸甚至无法形成裂缝，形成微地震事件在横向和纵向的不对称性；(5)当水平井与最大主应力方向不垂直时，微地震事件分布与水平段存在夹角，形成角度不对称。

Asymmetry analysis of microseismic monitoring results of horizontal well fracturing

To analyze the asymmetry of microseismic monitoring results of horizontal well fracturing and provide a basis for objectively evaluating the fracturing effect，this paper analyzes the microseismic monitoring results of 54 horizontal wells fracturing by combining fine geological research and engineering design. Data applied in this study include microseismic monitoring data，3D seismic data，logging data，and fracturing data. The paper summarizes the factors leading to the asymmetry of microseismic monitoring results of horizontal well fracturing and achieves the following findings. ①The factors leading to the asymmetry of microseismic monitoring results of horizontal well fracturing mainly include engineering reasons，geological reasons，and completed well distribution. The geological reasons include natural fractures，faults，lithologic changes，and crustal stress. ②Natural fractures and completed wells within the range of the fracture lengths can induce artificial fractures to change their directions. The artificial fractures will extend along the fracture development area and around completed wells. This leads to the asymmetric distribution of microseismic events on both sides of horizontal wells. ③Fault has two functions of inducing and shielding artificial fractures. The artificial fractures extend along the fault，and the microseismic monitoring events are distributed in a plane. The artificial fractures cannot extend to the other side of the fault and form a unilateral distribution far away from horizontal wells. ④The lithologic changes of vertical interlayers and in the horizontal direction control and block the extension of artificial fractures. They can inhibit the extension of artificial fractures to a great extent or even make fractures fail to form, which results in the asymmetry of microseismic events in the horizontal and vertical directions. ⑤There is an angle between microseismic events and the horizontal section when the horizontal well is not perpendicular to the direction of the maximum principal stress. This forms the angular asymmetry of microseismic events.