基于有限元软件的煤层气水平井井壁稳定数值模拟

Numerical Simulation of Wellbore Stability for CBM Horizontal Well by Finite Element Software

以山西宁武盆地的石炭系上统太原组9~#煤层为地质背景,该煤层煤岩力学性质为依托,运用COMSOL Multiphysics软件模拟分析了在欠平衡钻井中3种钻井液液柱压力下井周围岩的应力和变形情况。研究发现:研究区块水平井在垂向应力方向井周围岩所承受的应力最大,变形最为严重;井周围岩处存在应力突变点,该点处容易产生拉剪裂纹,导致井周围岩破裂或失稳;井周围岩应力分布及变形情况与钻井液液柱压力有关,液柱压力与储层压力差值越小,井周相对越稳定。

In this article, the No.9 coal seam of the Carboniferous upper Taiyuan formation is taken as geological background, the stress and deformation of the surrounding rock under three kinds of drilling fluid column pressure in under-balanced drilling was analyzed by using the finite element software COMSOL Multiphysics. The study shows that the stress and deformation of surrounding rock in the horizontal wells in vertical direction of the study block is the most severe. There is a sudden change of stress in the surrounding rock, which is easy to produce tensile and sheared crackles and lead to fracture or instability of the surrounding rock. The stress distribution and deformation of the surrounding rock are related to the drilling fluid column pressure,the smaller difference between the liquid column pressure and the reservoir pressure is, the more stability of the wellbore will.