三塘湖盆地致密油水平井增能压裂力学机理

Mechanical mechanism of horizontal well energized fracturing of tight oil in Santanghu Basin

重复压裂是三塘湖盆地油藏提高产能和采收率的必备手段。文中通过基于黏聚层单元的有限元数值模拟、室内岩石力学实验、声发射监测和岩石力学屈服破坏准则理论等手段,系统研究了该区块重复压裂改造中的增能力学机理。研究结果表明:增能压裂的核心是提升全局范围内地层孔隙压力,而暂堵转向是局部范围提升已有裂缝内的净压力,二者配合使用,使整体压力和局部净压力提升,在较大范围内激活天然裂缝系统。增能压裂的应力应变曲线特征、声发射特征呈现多次起伏波动和多次破裂特征,破裂压力相对较低。增能压裂裂缝扩展参数与地层孔隙压力提升比例、岩石力学参数及水岩相互作用时间等因素密切相关,其孔隙压力增加存在某一最优化值。

The refracturing stimulation is the necessary means to improve the reservoir productivity and recovery in Santanghu basin.In this paper,by means of finite element numerical simulation based on cohesive zone,the rock mechanics experiment in the laboratory,acoustic emission monitoring and the related Mohr-Coulomb yield failure criterion theory,the energized mechanical mechanism in the refracturing of this area is systematically studied.The result shows that the core of energized fracturing is to increase the pore pressure of the formation in the global scope,while the temporary plugging and diverting are to locally increase the net pressure in the existing cracks.The two methods are used together to make the overall pressure and the net pressure increased,which will activate the natural fracture system in a large range.The stress-strain curve and acoustic emission characteristics of energized fracturing show multiple fluctuations and multiple rupture characteristics,and the rupture pressure is relatively low.The parameters of crack propagation in energized fracturing are closely related to those factors such as the increase ratio of formation pore pressure,rock mechanics parameters and water-rock interaction time.There is also an optimum value for pore pressure increase.