基于瞬态热流固耦合的钻井井壁稳定性分析

Wellbore stability analysis in drilling process based on transient thermo-fluid-solid coupling model

王磊

WANG Lei

中国石化石油工程技术研究院有限公司，北京 102206

Research Institute of Petroleum Engineering Co., Ltd., SINOPEC, Beijing 102206, China

钻井过程中，钻井液循环对井壁和地层岩石产生热交换作用，同时钻井液滤失对地层产生渗流作用，两者都会引起井周应力场的改变，影响钻井液密度参数设计，严重时会导致井壁坍塌等复杂情况。文中根据线性热弹性多孔介质理论计算了温度变化对井壁和井周地层产生的井周热应力，依据达西渗流模型和渗流控制方程计算了瞬态条件下的地层孔隙压力和井周渗流应力，依据线性叠加原理求得了瞬态热流固耦合模型的井周应力，并利用摩尔￣库伦准则和抗拉强度准则分析了温度与渗流对井壁稳定性的影响。结果表明：钻井液循环对地层降温会降低地层坍塌压力和破裂压力，在井壁钻井液柱压力恒定的情况下，井周坍塌失稳区域减小，破裂失稳区域增大；钻井液向地层滤失渗流会增大地层坍塌压力和破裂压力，在井壁钻井液柱压力恒定的情况下，井周坍塌失稳区域增大，破裂失稳区域减小。计算结果对钻井过程中确定合理的钻井液密度和类型以维持井壁稳定具有指导意义。

The drilling fluid circulation will produce the heat exchange effect on the wellbore and stratum rock in drilling process, and the loss of the drilling fluid will produce seepage effect on the formation. The above two points will cause the change of the wellbore stress field, and will affect the design of drilling fluid density parameters and lead to complex conditions such as wellbore collapse and instability in serious cases. This paper calculated the thermal stress of wellbore and formation around the borehole caused by temperature changes based on the thermoelastic theory. The formation pore pressure and the seepage stress around the borehole under transient conditions are calculated according to the Darcy seepage model and seepage control equation. According to the principle of linear superposition, the stress around the borehole in the transient thermo-fluid-solid coupling model is obtained, and the Mohr-Coulomb criterion and tensile failure criterion are used to analyze the influence of temperature and seepage on the wellbore stability. The result shows that the cooling of the formation caused by drilling fluid circulation will reduce the formation collapse pressure and fracture pressure. Under the condition of constant drilling fluid column pressure, the collapsed area around the wellbore will decreases, and the fractured area will increases. The leakage of drilling fluid into the formation will increase the collapse pressure and fracture pressure of the formation. Under the condition of constant drilling liquid column pressure, the collapse area around the wellbore will expand and the fracture area will decrease. The calculation results have guiding significance for determining reasonable drilling fluid density and drilling fluid type in the drilling process, and maintaining the wellbore stability.

10.6056/dkyqt202302021