基于孔隙弹性力学理论的致密油气藏储层改造体积预测方法

储层改造体积预测对于致密油气藏体积压裂改造效果评估和施工参数优化设计具有重要意义。基于孔隙弹性力学理论和半解析的三维位移不连续法，综合考虑水力裂缝诱导应力，压裂液滤失引起的地层孔隙压力变化及其诱发的孔隙弹性应力的耦合效应，建立水力裂缝干扰模型下的地应力场预测模型，采用最大张应力强度准则和莫尔-库伦强度准则表征天然裂缝的张开与剪切破裂行为，将天然裂缝张开、剪切破裂波及体视为储层改造体，提出了一种预测致密油气藏直井体积压裂储层改造体积的半解析方法。研究结果表明：水力裂缝诱导应力和压裂液滤失引起的孔隙压力和孔隙弹性应力变化导致水力裂缝附近区域内的原始三向地应力发生改变，变化区域呈现椭球状；岩石本体破裂行为仅发生在水力裂缝边缘处的小范围区域内，天然裂缝的张开、剪切破裂才是形成储层改造体积的关键；实际储层改造体积形状近似于椭球体，现阶段现场常用的长方体等效方法并不合理；实例井研究验证了本方法的准确性与工程应用价值，可为致密油气藏体积压裂施工参数优化设计和压后产量预测提供有利的参考。

A prediction method of stimulation reservoir volume for tight oil and gas reservoirs based on poroelasticity theory

Stimulation reservoir volume prediction is of great significance for the evaluation of volume fracturing stimulation effect and the optimal design of construction parameters for tight oil and gas reservoirs. Based on the theory of poreelasticity and the semi-analytical three-dimensional displacement discontinuity method, the prediction model of Three-dimensional effective principal stress distribution under the interference of three-dimensional hydraulic fracture is established by considering the coupling effect of the induced stress of hydraulic fracture, the change of pore pressure caused by fracturing fluid leakage and the induced pore elastic stress. The maximum tensile stress intensity criterion and Mohr-Coulomb strength criterion are used to characterize the opening and shear failure behaviors of natural fractures, and the ripening bodies of natural fractures and shear fractures are regarded as stimulation reservoir volume. A semi-analytical method for predicting the stimulation reservoir volume of vertical well in tight oil and gas reservoirs is proposed. The research results show that the three-original principle effective stresses were altered by the combined contribution of the induced stress of hydraulic fracture, the increased pore pressure and poroelastic stress caused by fracturing fluid leak-off. the changed region of three-original principle effective stresses is quasi ellipsoid. Rock mass rupture occurs only in a small area at the edge of the hydraulic fracture, the opening and shear fracture of natural fractures is the key points for forming stimulation reservoir volume. It is not accurate to calculate the size of stimulation reservoir volume as a cuboid because the practical shape of stimulation reservoir volume is approximate ellipsoid. The accuracy of this prediction method was verified by the micro seismic monitoring results of the example well, which can provide a favorable reference for the optimal design of the operation parameters of volume fracturing and production prediction of tight oil and gas reservoirs.