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 CO_(2) huff and puff effects in tight oil considering component differences

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 CO_(2) huff and puff are unclear.In order to evaluate the development effect of CO_(2) 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 CO_(2) 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 CO_(2 )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 CO_(2),and the miscible system with strong dispersive ability is formed,and the heavy component tends to aggregate and distribute.CO_(2) 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 CO_(2)will increase pore space pressure and restrict the diffusion of alkane molecules.