基于流-固耦合的压裂裂缝形态影响因素分析

Analysis of factors influencing the shape of hydraulic fracturing fracture based on fluid-solid coupling

压裂裂缝形态易受储层物性、地应力、施工参数及压裂液黏度的影响.基于多孔介质流-固耦合的基本方程,根据损伤力学基本理论,利用cohesive黏结单元模拟压裂过程中裂缝起裂、扩展造成的损伤,以此建立水力压裂垂直裂缝扩展的三维有限元模型.模型可以对垂直缝扩展进行动态模拟,定量描述压裂过程中裂缝长度、高度、宽度.通过模拟发现:①储隔层弹性模量差值较小、施工排量过大、储隔层最小水平主应力差值较小均可能造成泥岩穿层,裂缝长度急剧下降,严重影响压裂效率;②渗透率对裂缝长度的影响最大,高弹性模量、低渗透的储层容易造长缝,但是高弹性模量、高渗透或高滤失的储层裂缝长度较短;③弹性模量对裂缝宽度的影响最大.

The geometric shape of fracture is important to economy and validity of hydraulic fracturing,and it is easily influenced by reservoir physical property,in-situ stresses,operation parameters and fracturing fluid property.A three-dimensional finite element model for simulating the propagation of a vertical fracture in hydraulic fracturing was established according to the basic theory of damage mechanics based on the fluid-solid coupling equations in porous medium.Cohesive elements are adopted in the model to simulate the reservoir damage caused by the initiation and propagation of fracture in fracturing process.Using the model can simulate the dynamic propagation of fracture and quantitatively describes fracture length,width and height in the hydraulic fracturing.The stimulation result shows that,(1) the difference between Young's modulus of reservoir and barrier bed,operation fluid rate and the difference between horizontal minimum main stress in reservoir and barrier bed may induce the fracture propagation in mud stone and the efficiency of hydraulic fracturing;(2) the permeability of reservoir has the largest influence on fracture length.Long fracture is easily produced in high Young's modulus and low permeability reservoir,while shorter fracture is easily produced in high Young's modulus and high permeability or high filtering loss reservoir;(3) Young's modulus has the greatest influence on fracture width.