水力压裂过程中纵向水力裂缝的形态研究

Hydraulic fracturing technology and horizontal well technology are proved to be effecient to increase production of unconventional hydrocarbon resources.For design and operation of hydraulic fracturing, it is extremely important to prevent the wellbore collapse and to determine the breakdown pressure. From an analysis of wellbore stress field together with Mohr-Coulomb criterion and The maximum tensile stress criterion, this work examines the critical fracturing fluid pressure for wellbore collapse and fracture initiation, initial crack surface. In computing the wellbore stress field, shale formation is treated as poroelastic solid medium, and the differential equations of the problem are derived by using Biot constitutive model. To solve the problem numerically, the discrete form of the differential equations is derived. Then, a user subroutine UEL of ABAQUS code is compiled to realize the numerical solving of the discretized differential equations. In this work, the law of wellbore breakdown under different ground stress states is analyzed. The research output of this work can help an optimal drilling design of shale gas well.