基于ABAQUS的三维水力压裂裂缝扩展规律研究

Study on fracture propagation law of 3D hydraulic fracturing based on ABAQUS

水力压裂是目前油气田开发中增产增注的关键技术,为研究裂缝起裂和扩张过程中裂缝形态的变化,利用ABAQUS有限元软件,通过嵌入Cohesive单元模拟裂缝扩展位置,系统分析了水平井裂缝扩展影响因素对裂缝几何形态的影响。研究表明,(1)当压裂液黏度由0.01 Pa·s增加到0.11 Pa·s时,缝长减小,缝宽增大,黏度大易形成短宽缝,黏度小则易形成长窄缝;(2)当压裂液排量较低时,难以达到地层破裂条件,排量较大时,地层开始扩展起裂,也容易形成新裂缝,采用变排量压裂,压力平稳式增长,有助于形成复杂裂缝网格;(3)当水平应力差由1 MPa增加到5 MPa时,缝长增大,缝宽和缝高减小,水平应力差增大,岩石破裂所需克服的阻力变小,易于起裂,而在压裂液压入的过程中,压裂液主要流经于裂缝延伸长度上。

At present,hydraulic fracturing is a key technology for increasing production and injection in oil and gas field development,in order to study the changes in fracture morphology during the initiation and expansion of fractures.Using ABAQUS finite element software,by embedding Cohesive units to simulate the position of fracture propagation,the influence of factors affecting fracture propagation in horizontal wells on fracture geometry was systematically analyzed.Research shows:①When the viscosity of fracturing fluid changes from 0.01 Pa·s increased to 0.11 Pa·s,the fracture length decreases and the fracture width increases.The high viscosity tends to form short and wide fractures,while the low viscosity tends to form long and narrow fractures;②When the fracturing fluid displacement is low,it is difficult to reach the formation fracture condition,and the displacement is relatively high,when the stratum starts to expand and crack,it is easy to form new fractures.Using variable displacement fracturing,the pressure increases steadily,which helps to form a complex fracture grid;③When the horizontal stress difference increases from 1 MPa to 5 MPa,the seam length increases.As the fracture width and height decrease,the horizontal stress difference increases,and the resistance required to overcome the rock fracture becomes smaller,making it easier to initiate fracture.In the process of fracturing hydraulic pressure,the fracturing fluid mainly flows through the fracture extension length.