基于数值模拟的径向井压裂裂缝形态

径向井压裂技术近年已取得良好开发成果,但该技术仍缺乏在致密气层的应用及研究。扩展有限元理论在水力压裂模拟上已有成熟的应用。基于地层流-固耦合方程,结合现场数据建立径向井水力压裂扩展有限元(XFEM)模型,研究裂缝起裂和扩展的规律。通过数值模拟量化分析了不同参数对裂缝形态的影响规律,明确了多径向井压裂的裂缝形态,并进一步提出了多径向井的优化布孔方案。结果表明:压裂时形成了沿径向井分布的诱导应力场,场内可一定程度实现主裂缝沿径向井方向定向扩展;垂向多径向井可有效提高径向井压裂裂缝形态的可控性;水平向多径向井的主裂缝形态由单径向井压裂主裂缝形态叠加而成,但径向井与水平最大主应力方向的夹角决定了该径向井处的起裂压力及裂缝扩展程度。研究成果对现场应用具有重要的指导意义。

CRACK MORPHOLOGY OF THE RADIAL WELL FRACTURING BASED ON THE NUMERICAL SIMULATION

Much better development effects have achieved for radial well fracturing technique in recent years,but the technology is still lack of the application and study in tight gas reservoirs.The extended finite element method (XFEM) has been maturely adopted in the hydraulic fracturing simulation.Based on fluid-solid coupling equation and integrating with the field data,the XFEM model for the radial well fracturing was established in order to research the laws of the fracture initiation and propagation.With the help of the numerical simulation,the influencing laws of different parameters on the fracture morphology were quantified and analyzed,the fracture morphology of the multi radial well fracturing was made clear,and moreover the optimized perforating scheme for the multi-radial well was put forward.The achievements show that for the induced stress field by the fracturing along the radial well,the directional extension of the key fracture can be realized to a certain deal along the well in the field;The vertical multi-radial wells can effectively improve the controllability of the fracture morphology;The key crack morphology of the horizontal multi-radial well is composed of the key morphology of the single radial well,but the included angle between the radial well and horizontal maximum principle stress determines the breakdown pressure and fracture extended degree in the radial well block.The study achievements possess important guiding significance for the field application.