Enhancing Sweep Efficiency Assessment for CO2 Plume Geothermal

Abstract

The CO\textsubscript{2} Plume Geothermal (CPG) Consortium was created in March 2023 to demonstrate the potential and technical feasibility of CO\textsubscript{2} Plume Geothermal at candidate sites in an integrated academic and industry synergistic collaboration. Following 12 years of theoretical CPG research, the consortium will execute a field demonstration in order to de-risk future commercial scale projects. Tracer campaigns performed during a field demonstration can provide information on how the plume evolves over time, which may be extrapolated in time and space to estimate the long-term, large-scale heat recovery potential for commercial CPG projects. Gas tracers, however, have not yet been employed for these purposes. Here we define the optimal tracer field campaign recommendations based on reservoir simulations of the Sleipner field in offshore Norway. We found that the determination of CO\textsubscript{2} plume development and sweep conformance was optimized using 7 tracers (N=7) in one-month intervals (dt=1). Additionally, we found that our homogeneous model possesses the largest sweep of the three models, as a uniform permeability permits greater flow of CO\textsubscript{2} at greater depths in the reservoir. Based on our results, we recommend injecting 35 kg (5 kg each) of 7 perfluorocarbon tracers over 5-6 hours in one-month intervals for determination of CO\textsubscript{2} plume development. However, for different reservoirs of interest, similar simulations, such as used in this study, should be run to identify a suitable number of tracers (N) and a suitable injection interval (dt) for determining CO\textsubscript{2} plume development and convergence for that site. From our findings, a tracer campaign would help reduce uncertainty in modelling, predictions and history-matching and improve understanding of sweep efficiency and long-term heat recovery. Tracer campaigns performed during a CPG pilot demonstration can then enhance the sweep efficiency assessment for a commercial CO\textsubscript{2} Plume Geothermal power plant.