Cross‐well pressure test analysis for CO₂ plume characterization based on arrival time and peak pressure change observations

Abstract

CO2 migration from the injection zone into an upper zone is possible through potential migration paths such as improperly abandoned wells or other weaknesses in the caprock overlying the injection zone. Various monitoring technologies may be used to obtain information on the resulting CO2 plume in an overlying zone. Cross‐well pressure testing—where water is to be injected/produced at a well and the pressure response to be observed at monitoring well(s)—has been previously investigated to characterize the CO2 plume. However, the methods proposed in the literature are not simple and may be computationally expensive either in forward modeling, inverse modeling, or both. For the cross‐well test analysis proposed herein, both the forward solution—a closed‐form analytical model—and the inverse model—a well‐posed overdetermined system of nonlinear equations—are simple. Consequently, a simple analysis methodology is presented to invert the cross‐well test data to obtain important information on the plume. To achieve this simplified approach, the migrated CO2 plume is assumed circular in shape with constant gaseous CO2 fraction over the plume area. The analysis methodology is first validated using a single‐phase model with a circular heterogeneity. Next, the methodology is applied to synthetic cross‐well pressure test data for a two‐phase system with CO2 plume. The arrival times and peak pressure change values from multiple monitoring wells are used to estimate the location and size of the plume. The estimated values are in good agreement with the actual plume size and locations used in generating the synthetic data. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.