Optimizing Reservoir Pressure Management with Relief Wells During CO2 Storage in Finite Aquifers

Abstract

Storing CO2 in deep saline aquifers is a viable technology to manage carbon emissions. However, in finite aquifers, reservoir pressure builds up quickly which can reduce injectivity and limit the ultimate storable quantities of CO2. Therefore, the purpose of this work is to investigate the optimum design for reservoir pressure-management wells during carbon dioxide (CO2) storage in finite aquifers using a numerical simulation method. In this paper, a synthetic aquifer model was used to investigate the optimal well placement and geometry, and well spacing to maximize CO2 storable quantities with a less total number of wells. Furthermore, the main target is to maximize the pore volume utilization and target injection rate per well without exceeding the reservoir fracture limit. A fit-for-purpose 3D reservoir simulation model used in this study was built to allow robust and accurate large-scale numerical simulation studies related to CO2 sequestration and storage using synthetic data. Multiple CO2 gas injectors were placed at the crest of the structure to utilize most of the available pore volume and maximize the injection rate. Various pressure management schemes were modeled and compared to find out the optimal design which can provide maximum injection rate and ultimate storage capacity. The results showed that well placement depth and the number of active relief wells both are playing a major role in maximizing the ultimate storage efficiency. Since reservoir heterogeneity and anisotropy can significantly affect the relief wells’ design, streamlines tracing can be very helpful to optimize the well spacing and orientation. After 80 years of injection, the simulation sensitivity study showed a significant difference (10-20% of CO2 storage efficiency) between the different pressure management schemes. In conclusion, relief wells are often needed to manage reservoir pressure build-up during CO2 storage in finite aquifers and their design is vital in maximizing the ultimate CO2 storage capacity. The outcome of this study is providing a useful guideline to optimize the field development plans and maximize the CO2 storage capacity in finite aquifers.