Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Sensitivity of Reservoir and Operational Parameters on the Energy Extraction Performance of Combined CO2-EGR–CPG Systems

Version 1 : Received: 31 August 2021 / Approved: 13 September 2021 / Online: 13 September 2021 (11:14:51 CEST)

How to cite: Ezekiel, J.; Kumbhat, D.; Ebigbo, A.; Adams, B.M.; Saar, M.O. Sensitivity of Reservoir and Operational Parameters on the Energy Extraction Performance of Combined CO2-EGR–CPG Systems. Preprints 2021, 2021090203 (doi: 10.20944/preprints202109.0203.v1). Ezekiel, J.; Kumbhat, D.; Ebigbo, A.; Adams, B.M.; Saar, M.O. Sensitivity of Reservoir and Operational Parameters on the Energy Extraction Performance of Combined CO2-EGR–CPG Systems. Preprints 2021, 2021090203 (doi: 10.20944/preprints202109.0203.v1).

Abstract

There is a potential for synergy effects in utilizing CO2 for both enhanced gas recovery (EGR) and geothermal energy extraction (CO2-plume geothermal, CPG) from natural gas reservoirs. This “combined CO2-EGR–CPG system” has been introduced as a feasible approach that constitutes a CO2 Capture double-Utilization and Storage (CCUUS) system. In this study, we carry out reservoir simulations, using TOUGH2, to evaluate the sensitivity of the natural gas recovery, pressure buildup, and geothermal power generation performance of the combined system to various key reservoir and operational parameters. The reservoir parameters include horizontal permeability, permeability anisotropy, reservoir temperature, and pore-size-distribution index; while the operational parameters include wellbore diameter and ambient surface temperature. Using an example of a natural gas reservoir model, we also investigate the effects of different strategies of transitioning from the CO2-EGR stage to the CPG stage on the energy-recovery performance metrics and on the two-phase fluid-flow regime in the production well. The simulation results show that overlapping the CO2-EGR and CPG stages and having a relatively brief period of CO2 injection but no production (which we call the CO2-plume establishment stage) achieves the best overall energy (natural gas and geothermal) recovery performance. Permeability anisotropy and reservoir temperature are the parameters the natural gas recovery performance of the combined system is most sensitive to. The geothermal power generation performance is most sensitive to the reservoir temperature and the production wellbore diameter. The results of this study pave the way for future CPG-based geothermal power-generation optimization studies. For a CO2-EGR–CPG project, the results can be a guide regarding the required accuracy of the reservoir parameters during exploration and data acquisition.

Keywords

CO2-plume geothermal (CPG); Enhanced gas recovery (EGR); Combined CO2-EGR–CPG system; Sensitivity analysis; Reservoir simulation; Geothermal power generation

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