油层压裂模拟的损伤力学方法及数值应用实例

为了充分发挥油层改造的效力，采用塑性损伤有限单元法，模拟水力压裂产生裂纹的扩展和分布情况，并以此为依据，对某油田长度为400m的致密砂岩储层中一条水平井多段压裂的段间距设计进行优化选择，并使用标量损伤从数学上表达注水压裂在油层中产生微裂纹的体积密度.数值计算中采用固液耦合的三维有限元格式来模拟渗流与变形的耦合力学行为.为了对压裂区进行准确模拟，计算中采用了子模型技术.计算结果中给出了给定注水速率时相应的三维损伤演化，同时给出了损伤场、孔隙压力场和主应力场的分布.根据数值计算结果，推荐的段间距为80m，这样400m的水平井段应该采用6段压裂.

Numerical method and application example of stimulation damage mechanics for fracture of reservoir formation

In order to sufficiently exert the efficacy of reservoir formation improvement, the propagation and distribution of cracks generated under hydraulic fracture were simulated with the plastic damage finite element method. In addition, the interva design for the multistage fracture of horizontal well in the tight sand reservoir of certain oil field with length of 400m was optimized and selected. The volume density of micro cracks in the reservoir formation caused by injection fracture was mathematically expressed with the scalar damage. A 3D finite element method （FEM） with solid liquid coupling was adopted in the numerical calculation, and the coupling mechanical behivor of transfusion and deformation was simulated. In order to accurately simulate the fracture region, the submodel technique was used in the calculation. The corresponding 3D damage evolution at the given injection speed was obtained in the calculated results. Meanwhile, the distribution of damage field, pore pressure field and main stress field was attained. According to the numerical calculated results, the recommended interval is 80m, and thus, 6 stage fracture is suggested for the horizontal well with the length of 400m.