Abstract

A mathematical model was presented to describe the injection of “warm” carbon dioxide into a porous geological formation that is initially saturated with methane and its hydrate with a negative (below the melting point of ice) temperature. A scheme in which three regions emerge in the formation was considered: a near region, which contains carbon dioxide and its gas hydrate; an intermediate region, which contains methane and ice; and a far region, which is saturated with methane and its hydrate. A system of equations was proposed, which included a continuity equation, a heat input equation, and Darcy’s law. Using this system, the effect of the initial pressure in the formation and its permeability on the mechanisms of generation of carbon dioxide hydrate was studied. Based on the obtained self-similar solutions, it was determined that the generation of CO₂ hydrate may occur by qualitatively different mechanisms, depending on the initial pressure in the system or the permeability of the formation. At low initial pressures, CH₄ hydrate decomposes into ice and methane, and CO₂ hydrate forms from ice and carbon dioxide. At low formation permeabilities, the generation of from water and carbon dioxide is accompanied by the emergence of an additional (fourth) region saturated with methane and water. Moreover, there may be a mechanism by which methane hydrate decomposes into water and gas, carbon dioxide hydrate forms from CO₂ and water, and three regions emerge. At high formation permeabilities and high initial pressures, carbon dioxide hydrate forms by a substitution mechanism, i.e., a direct transition of methane hydrate to carbon dioxide hydrate.

中文翻译：

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向含气水合物地层注入二氧化碳的数学模型

摘要

提出了一个数学模型来描述将“温暖的”二氧化碳注入多孔地质地层中，该地层最初被甲烷及其水合物饱和，温度为负（低于冰的熔点）。考虑了在地层中出现三个区域的方案：近区域，其中包含二氧化碳及其气体水合物；中间区域，包含甲烷和冰；以及一个被甲烷及其水合物饱和的远地区。提出了一个方程组，其中包括连续性方程、热输入方程和达西定律。利用该系统，研究了地层初始压力及其渗透率对二氧化碳水合物生成机制的影响。根据得到的自相似解，₂水合物可能通过性质不同的机制发生，这取决于系统中的初始压力或地层的渗透率。在低初始压力下，CH ₄水合物分解为冰和甲烷，而CO ₂水合物则由冰和二氧化碳形成。在低地层渗透率下，水和二氧化碳的生成伴随着另一个（第四）区域的出现，该区域被甲烷和水饱和。此外，可能存在甲烷水合物分解成水和气体的机制，CO ₂形成二氧化碳水合物和水，出现了三个区域。在高地层渗透率和高初始压力下，二氧化碳水合物通过替代机制形成，即甲烷水合物直接转变为二氧化碳水合物。