Simulation and Optimization of CO₂ Saline Aquifer Storage Injection Strategy

Abstract

As an effective way to reduce CO₂ emissions, saline aquifer storage can help China achieve the “dual carbon” target. However, the injection strategy can affect the CO₂ distribution in the reservoir, change the efficiency of different trapping mechanisms, and have an impact on sequestration safety. In this paper, based on the reservoir characteristics of the target saline aquifer in the South China Sea, the nature of supercritical CO₂, and the CO₂-water-rock interaction mechanism, the simulation model of a horizontal injection well in the saline aquifer was established first. Then the simulation schemes of continuous CO₂ injection, intermittent CO₂ injection, and water alternating gas (WAG) injection were designed and carried out. Last, the efficiency of different trapping mechanisms and sequestration safety under different injection strategies were compared and analyzed. The results show that compared with continuous CO₂ injection, WAG injection can reduce the structural trapping efficiency by 90.5%, increase the residual trapping efficiency by 30.9%, and reduce the total volume of CO₂ intrusion into the diffuse cap rock by 68.4%, followed by intermittent CO₂ injection, which are 38.3%,17.6%, and 46.1%. WAG injection is the most effective, which distributes more mobile CO₂ at the bottom of the reservoir and reduces the lateral transport distance underneath the cap rock, thus reducing the volume of CO₂ intruding into the cap rock and improving storage safety. This article optimizes the injection strategy through numerical simulation technology, which not only improves the effect and safety of CO₂ storage but also provides a theoretical basis for the implementation of saline aquifer storage projects.

Copyright 2023, IFEDC Organizing Committee.

This paper was prepared for presentation at the 2023 International Field Exploration and Development Conference in Wuhan, China, 20–22 September 2023.

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