重力分异和非均质性对天然气藏CO2埋存的影响——以中国南方ＸＣ气藏为例

在含CO₂的天然气藏中实施CO₂长期稳定埋存并提高天然气采收率，实现CO₂的规模化综合利用，具有重大的现实意义。为此，以一个真实的含CO₂浅层废弃气藏为埋存靶场，运用数值模拟方法，设计了纵向非均质气藏剖面模型，用于研究气藏储层在正韵律、反韵律以及复合韵律条件下气体运移对超临界CO₂稳定埋存的影响，并重点研究了重力分异和地层非均质性条件下的流体运移规律。结果表明：不同韵律剖面模型在注超临界CO₂埋存及开采剩余天然气过程中，作为反韵律的目标气藏注超临界CO₂埋存过程在生产井突破最晚，吸入的超临界CO₂量最大，天然气累计采出量最多，其超临界CO₂埋存潜力相对最大；重力分异可引起超临界CO₂与天然气之间产生非平衡态相的分离，天然气向气藏高部位运移，CO₂最终趋向于形成“超临界CO₂垫气”，可以很稳定地沉积在气藏下部形成“垫气”埋存。该成果为实现CO₂减排、降低CO₂捕集与埋存技术（ＣＣＳ）成本提供了技术支撑。

Influence of gravity differentiation and heterogeneity on CO2 sequestration in gas reservoirs:A case of the XC Gas Reservoir in South China

It is no doubt of great practical significance to implement the long-term stable CO₂ sequestration in natural gas reservoirs containing CO₂, enhance gas recovery, and achieve large-scale utilization of CO₂. In this paper, a real deserted shallow gas reservoir containing CO₂ of XC in South China was taken as a case of study. Numerical simulation was first employed to design a model of longitudinal heterogeneous gas reservoir profile to study the influence of gas migration under positive rhythm, reverse and composite rhythm conditions on the stability of supercritical CO₂ sequestration. With focus on the fluid migration rules under gravity differentiation and formation heterogeneity, we concluded the following results. (1) Among different rhythm profile models in gas injection in supercritical CO₂ sequestration and the exploitation of remaining natural gas, the target reservoir of reverse rhythm was the last one among which the supercritical CO₂ sequestration was broken through in producing wells; the absorbed volume of supercritical CO₂ was the largest, and the cumulative gas production was the maximum, indicating that the potential supercritical CO₂ storage volume might be the highest in that reservoir. (2) The gravity differentiation could cause the phases separation between supercritical CO₂ and natural gas because of the non equilibrium phase behavior, the natural gas moved towards the upper area of a gas reservoir, and the supercritical CO₂ eventually tended to form a “cushion” and was deposited steadily on the bottom of the reservoir. This study provides a technical support for the minimization of CO₂ emission and carbon capture and storage (CCS) cost.