地层各向异性对CO2在含水层中迁移转化的影响

在CO2驱油封存过程中，封存的CO2可能通过盖层中的裂缝泄漏到浅层含水层。文章以延长油田杏子川化子坪试验区白垩系洛河组砂岩含水层为例，采用数值模拟软件TOUGHREACT研究地层各向异性对CO2在浅层含水层中迁移转化的影响。结果表明：溶解矿物为方解石、伊利石、奥长石、钾长石、绿泥石和赤铁矿，其中伊利石从第10年开始沉淀，沉淀矿物为石英、高岭石和钠蒙脱石，次生矿物为菱铁矿和钙蒙脱石。地层垂向与水平渗透率比值kv/kh（kv保持不变）越大，CO2在水平方向上的迁移扩散距离越小，含水层中溶解态CO2浓度越高，pH值越低，CO2突破浅层含水层的时间越短。通过研究地层各向异性对CO2在浅层含水层中迁移转化的影响，为驱油封存CO2泄漏监测和风险预警提供科学依据。

Study on the Effect of Formation Anisotropy on CO2 Migration and Transformation in Shallow Aquifers

In the process of carbon capture, utilization and storage, the sequestered CO2 may break leak to the shallow aquifers through the cracks in the caprock. Based on the sandstone aquifer of Cretaceous Luohe formation in Xingzichuan Huaziping area of Yanchang Oilfield, numerical simulation method was used to study the effect of formation anisotropy on CO2 migration and transformation in the shallow aquifer during carbon capture, utilization and storage. The research results show that the dissolved minerals are calcite, illite, oligoclase, K-feldspar, chlorite and hematite, among which illite began to precipitate from the 10th year, the precipitated minerals are quartz, kaolinite and smectite-Na, and the secondary minerals are siderite and smectite-Ca. The larger the ratio of vertical to horizontal permeability kv/kh (kv remains constant) of the formation, the smaller the migration and diffusion distance of CO2 in the horizontal direction, the larger the concentration of dissolved CO2 in the shallow aquifer, the lower the pH value, and the shorter the time for CO2 to break through the shallow aquifer. By studying the influence of formation anisotropy on the migration and transformation of CO2 in shallow aquifers, it provides a scientific basis for the monitoring and risk warning of CO2 leakage during carbon capture, utilization and storage.