Abstract: A finite element simulation model for dynamic fracture creation was established on the basis of the fluidsolid coupling theory for porous media. The creation of dynamic fractures with different geometry was simulated with finite element method. The research results demonstrated that a tight zone as elliptic distribution was developed around the wellbore during the creation of dynamic fracture. For the wedge fracture and elliptic fracture, the dimension of influence region by fracture creation increased with the fracture width increasing near the fracture tip, and the distribution of the influence zone was similar to ellipse. The permeability in the region less than 5m away from the wellbore axis was influenced dramatically. The more adjacent to the wellbore axis, the more sensitive the permeability alteration would be observed. At the same time, the Darcy velocity decreases noticeably in the tight zone near wellbore. The fracture with shorter length would result in the more sensitive for the productivity alteration of fractured wells. The formation of tight zone by dynamic fracture creation is an important factor for inducing the declination of productivity of fractured wells.

Key words: fluidsolid coupling, hydraulic fracturing, fracture geometry, dynamic fracture creation, permeability, Darcy velocity, finite element simulation, mathematical model

摘要： 基于多孔介质流固耦合理论,建立了水力压裂动态造缝有限元模型,对不同裂缝形态的动态造缝进行了有限元模拟。研究结果表明:动态造缝会在井眼周围形成类似于椭圆形分布的致密带。对于楔形缝及椭圆缝来说,随着靠近裂缝尖端造缝宽度的增加,造缝影响区域有所扩大,但总体分布仍类似于椭圆形。在井眼周围5m以内区域,渗透率受动态造缝影响明显,且距井眼越近,渗透率变化越剧烈;在近井致密带内渗流速度明显降低,且造缝长度越小动态造缝对压裂井产能的影响相对越明显。动态造缝形成的致密带是降低压裂井产能的一个重要因素。

关键词: 流固耦合, 水力压裂, 裂缝形态, 动态造缝, 渗透率, 渗流速度, 有限元模拟, 数学模型