高温井地层温度变化对井壁稳定性影响规律研究

Law of temperature influence on weilbore stability in hot well

高温井钻井过程中保持井壁稳定的关键是确定合理的钻井液密度范围 ,而确定地层坍塌压力和破裂压力的常规方法中并没有考虑地层温度变化的影响 ,为安全钻井带来了隐患。从钻井过程中井壁及地层温度场的数值模拟和附加温变应力下井壁周围应力场的计算出发 ,研究了井壁及地层温度变化规律和井周围岩应力状态。依据控制体单元能量守恒原理建立了钻井过程中井壁及地层温度场控制方程 ,并利用有限差分法对控制方程进行了离散 ,并对数值求解方法进行了优化 ,实现了温度场的快速计算。依据孔隙介质热弹性理论对井壁周围的应力分布规律进行了计算 ,结合地层的强度准则确定了考虑温度变化情况下地层坍塌压力、破裂压力的计算模型 ,为高温井安全钻井液密度窗口的设计提供了依据。

In the drilling and completing process of hot well, the key to sustain the hole in stable condition is to design reasonable drilling fluid density window, but in the conventional calculation of caving pressure and fracture pressure, influence of the formation temperature change is not taken into consideration, which may cause potential troubles in drilling. In this paper, temperature change of the wellhore and the formation, as well as the stress of circumferential rock were studied based on numerical simulation of temperature field of the hole and the formation, and the calculation of circumferential stress field with additional temperature strain. Temperature field governing equation on the hole and the for mation during drilling was established based on control element conservation of energy principle, and the governing equation was dispersed using finite difference method and the numerical calculation was optimized to produce fast solution.In additional, the law of stress distribution on circumferential field was calculated according to porous medium thermoelasticity principle, and incorporated with strength regulation of the formation, the calculation model of caving pressure and fracture pressure was determined, providing fundamental for designing safedrilling fluid density window for hot well drilling.