关键词: 欠平衡钻井, 流-固-热三场全耦合, 井底岩石应力状态, 有限单元法, 数值模拟

Abstract:

Compared with conventional drilling, the higher speed of underbalanced drilling correlates closely to the stress state of bottom-hole rocks to be broken up, and the stress is co-affected by both pore pressure and temperature of strata. Based on the theory of a fully coupled thermal-hydro-mechanical field, the present paper simplified coupled equations according to the actual state of bottom rocks to be broken up in underbalanced drilling, and with the combination of boundary conditions corresponding to the stress analysis of bottom-hole rocks, it used the finite element method to explore the mechanism of influence exerted by pore pressure and temperature of strata on the stress state of bottom-hole rocks. The results showed that every principal stress of bottom rocks decreased with decreasing the drilling fluid pressure and temperature of bottom rocks, in which the reducing degree was related with differences in pressure and temperature, the more the differences, the greater the reducing degree of each principal stress of bottom rocks, moreover, the reducing rate was related with the permeability and thermal conductivity of rocks, the higher the permeability and thermal conductivity, the faster the change of each principal stress of bottom rocks, while the efficiency of breaking rocks assisted by pore pressure of strata was relatively lower.

Key words: underbalanced drilling, fully coupled thermal-hydro-mechanical model, stress state of bottom-hole rock, finite element method, numerical simulation