CO_2注入引起井筒周围岩石损伤的热孔弹耦合分析

THERMO-POROELASTIC COUPLING ANALYSIS OF ROCK DAMAGE AROUND WELLBORE DUE TO CO_2 INJECTION

以岩石的耦合–去耦合解析为主线,在三场耦合方程中导入损伤变量,建立岩石损伤过程中的热孔弹耦合模型。通过把均质弹性介质材料的热孔弹耦合模型的有限元解同去耦合解析解的对比,验证有限元数值解的精确性。然后,利用该耦合模型研究CO2注入后井筒周围的应力状态和损伤情况。最后,针对服从Weibull分布的非均质岩石材料,研究CO2注入后非均质岩石渗流性质的改变。结果表明,超临界CO2的注入会对岩石的强度和渗透性产生影响,较高的注入速率会引起岩石的受拉破坏并导致拉伸损伤范围的扩大。非均质材料更容易发生岩石的损伤和渗透性增加。

A coupled thermo-poroelastic model is thermo-poroelastic model is firstly utilized to proposed with integration of a damage factor. The proposed simulate the thermo-hydro-mechanical（THM） response of homogeneous elastic mediums and its accuracy of the numerical resuks is verified through comparing to the decoupled analytical solution. Secondly, the thermo-poroelastie model is employed to predict stress response and damage propagation around the wellbore due to CO2 injection. Finally, this model is applied to heterogeneous rock under a Weibull distribution to predict stress response and permeability change. The experimental results indicate that the supercritical CO2 injection can change the rock＇s strength state and permeability distribution significantly. Too high injection rates will facilitate the tensile damage and extend the tensile damage zone. Heterogeneous rock material is more vulnerable .to tensile damage and permeability increase.