热采过程中井眼热应力定量评价方法

Quantitative evaluation method for thermal stress around borehole during thermal recovery

应用连续介质力学理论,建立了与蒸汽注入过程相关的热-流-变形耦合问题的基本数学模型;应用全隐式顺序有限元数值解方法,对该数学模型进行了求解,获得了井眼热应力与超孔隙地层压力的部分数值结果。结果表明,在300℃注入蒸汽温度情况下,由温度变化引起的井眼区域超孔隙压力可以达到15MPa的水平。由于低渗透页岩地层流体高温膨胀导致的超孔隙压力,有可能产生有效拉张应力,严重时会导致地层破裂。

Based on the continuous medium mechanics theory, a basic mathematical model of coupled thermal - hydraulic - deformation related to steam injection process is built. A finite element method with fully implicit and sequential iterative algorithm is used to compute this complicated model. Some numerical results of borehole thermal stress and super pore pressure are gained. The results show that the super pore pressure at borehole area caused by the temperature will reach to 15MPa at 300℃ injected steam temperature. Due to the higher thermal expansion of fluid in low permeability shale, the super pore pressure may lead to the development of effective tensile stress and even formation fracturing.