超临界CO<sub>2</sub>渗流的流-固-热多场耦合机理研究

Abstract

<p indent="0mm">Clay swelling and dispersion easily occur when encountering water for shale formation, resulting in problems related to wellbore collapse when using water-based fluids, such as drilling fluid or poor fracturing stimulation when using water-based fluids as the fracturing fluid. Supercritical carbon dioxide (ScCO₂) can effectively protect the clay from hydration and avoid formation damage. Based on this, basic research studies have been performed by researchers regarding the exploitation of shale oil and gas resources using ScCO₂. The multi-physics coupling model describing the water seepage process cannot explain the ScCO₂ seepage because of a great variation in the physical properties of CO₂ with temperature and pressure. To construct multi-physics coupling models capable of reflecting the ScCO₂ seepage process when developing oil and gas resources using ScCO₂, the thermal-hydro-mechanical coupling models are established in this study based on the transport and thermodynamic properties of ScCO₂, combined with the law of effect of ScCO₂ dissolution on the mechanical properties of shale. The finite element method is used to study the distribution of formation temperature, pore pressure, and stress with time and location of ScCO₂ seepage, and the comparison of multi-physics fields is performed between ScCO₂ and water seepage. The results indicate that the compared with water seepage, the formation temperature variation of ScCO₂ seepage is greater, the pore pressure is lower, the stress difference near the wellbore in the direction of minimum <italic>in</italic>-<italic>situ</italic> stress is bigger, and the tangential stress in the direction of maximum <italic>in</italic>-<italic>situ</italic> stress is lower. This study can provide theoretical basis for wellbore stability analysis when using ScCO₂ as the drilling fluid and fracturing design and evaluation when using ScCO₂ as the fracturing fluid.