Abstract:

In order to have in-depth understanding of the influences of heterogeneous porous structure inside saline aquifers during carbon dioxide injection，a two-phase flow mathematical model was proposed to describe the imbibition process of the supercritical carbon dioxide-brine system，in which a lognormal distribution of porosity was introduced to represent heterogeneity of porous saline aquifers.The model also featured the imbibition process at varying densities and viscosities of supercritical carbon dioxide that were correlated to local pressure and temperature of saline aquifers.Numerical simulations were conducted to investigate the influences of process parameters during injection and characteristics of saline aquifers on injecting behavior and saturation distributions of supercritical carbon dioxide in the saline aquifers.The results showed that injection pressure was dependent on the depths and volumetric average porosities of saline aquifers.It was less affected by the porosity distribution of the saline aquifer.However，the saturation distributions of supercritical carbon dioxide in saline aquifers were strongly affected by the porosity distribution.When the total volumes of saline aquifers were identical，the storage capacity of a deep saline aquifer was less than that of a shallow aquifer，whereas the injection pressure in the former case was larger than that in the latter case.For the purpose of maximizing the storage efficiency，an appropriate injection rate needed to be chosen during carbon dioxide injection.The proposed method would provide an insight into carbon dioxide sequestration in saline aquifers，and it would also be a tool for evaluating the consequence of injection.

Key words:

CO₂封存, 非均质盐水层, 注入, 数值模拟

摘要：

为了研究盐水层孔隙结构特性对CO₂注入过程的影响，采用对数正态分布的随机分布孔隙率表征地下盐水层的非均质孔隙特性，引入与盐水层中局部温度和局部压力相适应的CO₂密度和黏度，建立了超临界CO₂-盐水体系的两相流驱替过程数学模型。通过数值模拟研究了超临界CO₂注入的过程参数和盐水层特性对CO₂注入特性和盐水层中饱和度分布的影响。研究表明：CO₂的注入压力主要与盐水层的深度和盐水层的体积平均孔隙率有关，而受盐水层孔隙率分布的影响较小;盐水层的孔隙率分布特性对CO₂饱和度分布影响非常显著;在盐水层总容积相同的条件下，深层盐水层的CO₂存储容量比浅层盐水层的小，且注入压力大;在CO₂封存过程中，应选择合适的注入速率，最大限度地提高盐水层封存容量的利用率。本文的计算方法和分析结果为超临界CO₂的地下封存过程和注入后的评估方法等提供了计算方法和理论依据。

关键词:

CO₂封存, 非均质盐水层, 注入, 数值模拟