前置CO压裂后砂砾岩CO驱油的三维孔隙尺度模拟

3D pore-scale simulations of CO flooding after pre-flushing CO fracturing in glutenite reservoirs

杨柳 姜晓宇 董广涛 公飞 朱凯 裴奕杰 蔡嘉伟

Liu YANG Xiaoyu JIANG Guangtao DONG Fei GONG Kai ZHU Yijie PEI Jiawei CAI

准噶尔盆地玛湖凹陷具有巨大的油气开发潜力，但由于储层非均质性强、产量递减快。目前前置CO压裂-气驱-封存协同技术（PCFS）是砂砾岩储层强化开采的常用方法。为了研究前置压裂过程中CO-水-岩相互作用对孔隙结构的影响以及气驱过程中CO的运移规律，选取了玛湖凹陷砂砾岩岩心，开展了CO浸泡实验、高精度Mirco-CT扫描以及基于流体体积法（VOF）的3D数字岩心两相流数值模拟。研究结果表明：①CO-水-岩相互作用会导致砂砾岩孔隙结构发生溶蚀扩展，原本孤立的孔隙通道逐渐汇聚成为片状，从而扩大了CO团簇的波及范围。该过程也引发了二次矿物沉淀和膨胀，进而导致流动通道的堵塞或重组，改变流体在孔隙结构内的流动路径和速度，阻碍优势流道的形成。②CO浸泡导致孔隙空间溶蚀扩展所起到的积极作用要大于二次矿物沉淀和膨胀所引起的消极作用，增加渗透率，孔隙结构的渗流能力呈现出增强趋势。在不同流道中，CO团簇具有凸形和凹形等不同的驱替前缘形态。浸泡前、后代表性单元体（REV）模型无因次数（，，）对驱替效率的影响程度不同。在浸泡后孔隙发育程度相对较高的REV模型中，驱替效率对无因次数（，，）变化的敏感性较强，表明PCFS技术在孔隙发育程度较高的储层中具有更好的应用效果。

The Mahu Sag in the Junggar Basin holds significant potential for oil and gas exploitation and development. However， the strong reservoir heterogeneity therein leads to a rapid decline in oil and gas production. Presently， the pre-CO fracturing， gas flooding， sequestration （PCFS） synergistic technology is commonly employed for enhanced oil recovery from glutenite reservoirs. This study aims to investigate the impact of CO-water-rock interactions on pore structures during pre-flushing CO fracturing， as well as CO migration patterns in the process of gas flooding. Using a glutenite core taken from the Mahu Sag， we perform CO soaking experiments， high-precision micro-computed tomography （micro-CT）， and volume of fluid （VOF） method-based numerical simulations of two-phase flow in 3D digital cores. The results indicate that CO-water-rock interactions facilitate the dissolution-derived expansion of the pore structure， and the originally isolated channels converge into sheets， increasing the sweep range of CO clusters. Meanwhile， this process induces secondary mineral precipitation and expansion， which can block or restructure pathways for fluid flow and， accordingly， change the flow paths and velocity of fluids in the pore structure. These， thereby， hinder the formation of the preferential flow pathways. Nevertheless， compared to the negative impact of secondary mineral precipitation and expansion， the pore space expansion under CO soaking-induced dissolution is greater in positive effect. Specifically， the permeability is improved， so does the seepage capacity of pore structures. CO clusters in different flow channels exhibit different morphologies （like convex or concave） at the displacement front. In the representative elementary volume （REV） models before and after CO soaking， the dimensionless parameters （i.e.， capillary number ， contact angle ， and viscosity ratio ） exert varying degrees of influence on the displacement efficiency. Specifically， in the REV model after CO soaking， exhibiting a relatively higher degree of porosity evolution， the displacement efficiency is more sensitive to changes in the dimensionless parameters. This indicates that the PCFS synergistic technology is more effective in the exploitation of reservoirs with higher-degree porosity development.

10.11743/ogg20250222