考虑组分差异的致密油二氧化碳吞吐效果分子模拟

Molecular simulation of CO2 huff and puff effects in tight oil considering component differences

任旭,王杰,董海海,盛萍,徐虎,张鸿英

中国石油新疆油田分公司勘探开发研究院，新疆 克拉玛依 834000 中国石油新疆油田分公司采油二厂，新疆 克拉玛依 834000 中国石油吉林油田分公司勘探开发研究院，吉林 松原 138000）

Exploration and Development Research Institute, Xinjiang Oilfield Company, PetroChina, Karamay 834000, China NO.2 Oil Production Plant, Xinjiang Oilfield Company, PetroChina, Karamay 834000, China Exploration and Development Research Institute, Jilin Oilfield Company, PetroChina, Songyuan 138000, China)

分子模拟可描述致密油储层纳微孔隙中的流体扩散与运移行为，然而不同烃类组分（轻质、重质）对二氧化碳吞吐开发的响应特征尚不清晰。为评价二氧化碳吞吐对致密油中不同组分的开发效果，运用分子动力学方法，探讨了其分子运动与扩散特征，研究了不同孔隙、压力下二氧化碳摩尔分数对采收率的影响，并结合轻质与重质组分在石英孔隙表面的吸附/解吸差异性行为、烃类分子扩散系数随二氧化碳摩尔分数的变化，揭示了其开发机理。结果表明：轻质组分更易被二氧化碳置换，并形成分散能力强的混相体系，重质组分倾向于聚集分布；二氧化碳吞吐有利于在更小的压降条件下达到良好开采效果，其机理主要是增强了烷烃分子的扩散能力，但过量的二氧化碳使得孔隙空间压强升高，从而导致烷烃分子的扩散受到限制。

Molecular simulations can be used to describe fluid diffusion and migration in nanopores of tight oil reservoirs. However, the response characteristics of different hydrocarbon components (light/heavy) to CO2 huff and puff are unclear. In order to evaluate the development effect of CO2 huff and puff on different components in tight oil, the molecular motion and diffusion characteristics were discussed based on molecular dynamics method, and the influence of CO2 volume mole fraction on recovery under different pore sizes and pressures was studied. The adsorption/desorption behavior of light and heavy components on quartz pore surface and the variation of diffusion coefficient of hydrocarbon molecules with the molar fraction of CO2 were combined to reveal the development mechanism. The results show that the light component is more likely to be replaced in the competitive adsorption with CO2, and the miscible system with strong dispersive ability is formed, and the heavy component tends to aggregate and distribute. CO2 huff and puff is beneficial to achieve good exploitation effect at lower pressure consumption, and its mechanism mainly lies in enhancing the diffusion ability of alkane molecules. However, excessive CO2 will increase pore space pressure and restrict the diffusion of alkane molecules.

10.6056/dkyqt202202015