深部咸水层二氧化碳封存的干化效应及选址启示

将二氧化碳注入到深部咸水层中，形成复杂的多组分、多相流系统。二氧化碳在压力梯度、浓度差作用下不断扩散，逐步带走盐溶液中的水分，导致各组分的相态变化，盐结晶析出，阻塞了咸水层孔隙通道，从而降低了二氧化碳的注入效率，研究该干化效应的影响因素并为工程选址提供依据具有重要意义。采用二维径向模型建立多相流体的流动方程，并结合相对渗透率和毛细压力方程探讨二氧化碳注入速率、咸水层含盐量、毛细压力的特征参数对干化效应的影响，干化效应可用固体饱和度值进行定量描述。结果表明：二氧化碳运移分3个区域：干涸区、气液相混合区及液相咸水区，干化效应主要发生在井周的干涸区。在毛细作用下固体饱和度随注入速率的减小而增大，随咸水层含盐量增大而增大，随毛细作用增大而增大。因此，提高二氧化碳的注入速率，向咸水层中注水稀释含盐量或选择粒径较大的均质咸水层减小毛细作用，均可降低盐结晶对孔隙通道的阻塞，提高注入效率。

Dry-out effect and site selection for CO2 storage in deep saline aquifers

Deep saline aquifer is a complex multi-components and multiphase flow system after CO2 injection. CO2 advection happens because of pressure gradient and velocity difference and dries out water in saline aquifer, which changes phases of the components and causes salt precipitation. The precipitated salt clogs the pore space in aquifer and decreases CO2 injectivity, so it is very important to research the effect on dry-out problem and site selection. 2D radial model is built and multiphase fluid flow function is established. By considering relative permeability function and capillary pressure function, the effects of CO2 injection rate, salty in aquifer, input maximum capillary pressure and characteristic parameters of capillary pressure on dry-out problem are studied. The dry-out problem can be quantitatively described by solid saturation. Results show that CO2 migration separates the aquifer into three domains: dry-out domain, gas and liquid mixture domain and liquid saline aquifer domain. The dry-out problem happens nearby the injection well. If capillary pressure is considered, the solid saturation will increase when injection rate decreases, salty in aquifer increases, or capillary pressure increases. As a result, increasing CO2 injection rate, injecting water into aquifer before CO2 injection, and decreasing capillary pressure by choosing a large pore size homogenous formation can avoid the clogging of pore space with salt precipitation, which enhances CO2 injectivity.