热采过程中地层超孔隙压力与井眼应力的定量评价

A quantitative evaluation for excess pore pressure and wellbore stress around a cased well under steam injection

基于连续介质力学理论,建立了热采蒸汽注入过程中地层超孔隙压力和有效应力定量评价的热流变形耦合数学模型,应用Galerkin有限元全隐式顺序迭代方案,建立了求解该类复杂耦合模型的有效数值解法。数值结果表明,当井筒加热速率为46.82℃/d时,低渗透页岩地层的最高超孔隙压力达13.8 MPa,相应的页岩层径向有效应力和周向有效应力分别达到了14 MPa和9 MPa。因此,设计注入蒸汽加热速率的最佳方案应综合考虑页岩的热流动力反应、地应力水平和套管强度等因素。

Based on the continuum mechanics theory, a coupled thermal-hydraulic-mechanical model corresponding to excess pore pressure and effective stress of thermal well under steam injection, was presented. In order to derive an effective numerical solution, a Galerkin finite element method with fully implicit and sequential iterative algorithm was adopted to design related computer codes. The numerical results show that excess pore pressure around cased well reaches 13.8 MPa when the heating rate reaches 46.82 ℃/d. Thereby the effective stress near the well approaches the maximum value of radial stress with 14 MPa, tangential stress with 9 MPa, respectively. Therefore, an optimum programming for warming time or heating rate in steam injection should include various factors such as thermal-hydraulic response, in-situ stress and the strength of casing structure.