应力阴影效应对水平井压裂的影响

为揭示水平井分段改造中的应力阴影效应及其影响因素,基于水平井分段体积改造理论,借鉴Bunger的应力场分析假设条件,从水平井单一横切缝入手,建立起了考虑应力阴影的应力场叠加数学模型并推导出数学公式,在此基础上得出简化的水平井多段应力阴影效应应力场模型。对应力阴影效应影响因素的分析结果表明:储层地质参数中杨氏模量、水平主应力差对应力阴影效应的影响大,而泊松比对其影响则很小;施工参数中施工排量对应力阴影效应的影响明显,在一定储层条件下,分段及簇间距越小,应力阴影效果对水平井裂缝附近其他裂缝的扩展产生应力阴影影响越大。利用该研究成果对现场实际水平井压裂进行了优化设计,微地震监测结果表明:利用应力阴影效应只压裂6段就实现了以往10段压裂的改造体积,较之以往减少压裂4段,节约成本在30%以上。这对合理利用应力阴影效应进行水平井体积改造裂缝尺寸设置及工艺参数优化具有重要的指导意义。

Influence of stress shadow on horizontal well fracturing

In order to reveal stress shadow effect and its influencing factors in the processing of segregated fracturing in horizontal wells, starting with an analysis of single transverse fracture of horizontal wells, we established a stress field superposition model and developed a mathematical formula considering stress shadow according to the theories of segregated SRV (stimulated reservoir volume) fracturing in horizontal wells and stress field analysis assumed conditions proposed by Bunger. On this basis, a simplified stress field model was established for the segregated stress shadow of a horizontal well. The influencing factor analysis shows that among reservoir geological parameters, Young's modulus and horizontal principal stress difference greatly impact stress shadow, while the Poisson's ratio slightly affects stress shadow; among construction parameters, the displacement obviously affects stress shadow; in certain reservoir conditions, the smaller the distance between the segments clusters, the stronger stress shadow on the extension of other fractures around horizontal well fractures. The research results were used to optimize the design of actual horizontal wells. Micro seismic monitoring indicated that stress shadow reduced three to four segments to achieve the same stimulated reservoir volume, with the cost saved by more than 30%. Therefore, it is of an important guiding significance for engineers to rationally use stress shadow to optimize fracturing design and process parameters during horizontal well fracturing.