电爆冲击波对储层致裂效果影响因素的数值模拟研究

Numerical simulation study of the influencing factors of electric explosion shock waves on reservoir fracture initiation

摘要:

电爆冲击波在油气储层增渗解堵中具有巨大应用潜力，为了解各因素对电爆冲击波致裂效果的影响程度，本文采用ANSYS/LS-DYNA软件，通过改变地应力、弹性模量、抗拉强度参数进行数值模拟。结果显示，地应力对致裂效果具有强烈的抑制作用，在双向等压地应力作用下，裂纹区形状为圆形，并且随着地应力的增大，岩体破裂度、破裂半径均逐渐减小。在双向不等压地应力作用下，随水平主应力差值增大，裂纹扩展方向由圆形逐渐转变为椭圆形，具有沿最大水平主应力方向扩展的特点；弹性模量对致裂效果具有重要影响，随着弹性模量的增大，岩体破裂度、破裂半径均呈增大趋势；随抗拉强度增大，岩体破裂度、破裂半径均减小。

Abstract:

The electric blast shock wave has great application potential in increasing permeability and removing plugs of oil and gas reservoirs. In this paper, ANSYS/LS[CD*2]DYNA software is used to investigate the influencing factors of electric blast shock wave induced cracks through variation of the in situ stress, elastic modulus and tensile strength. The simulation results show that the in situ stress has a strong inhibitory effect on crack propagation. Under action of the two way isobaric in situ stress, the shape of the crack zone is circular, and with increase of the in situ stress, the fracture degree and fracture radius of the rock mass decrease gradually. Under action of the bi directional unequal compressive in situ stresses, as the difference between the horizontal principal stresses increases, the direction of crack propagation gradually changes from circular to elliptical, exhibiting the characteristic of extending along the direction of the maximum horizontal principal stress. The elastic modulus has important effect on crack initiation: with increase of the elastic modulus, the fracture degree and fracture radius of the rock mass increase. As the tensile strength increases, the fracture degree and fracture radius of the rock mass decrease.