Numerical Assessment of CO2-Circulated Geothermal Production from a Closed Reservoir System

Abstract

Renewable energy is becoming more attractive to meet energy demands due to increasing concerns about carbon dioxide (CO2) emission, environmental pollution, and exhaustion of oil/gas reserves. In addition to oil and solar energy sources, Oman also has abundant low-enthalpy geothermal energy resources in the northern mountain region to be explored and utilized. In the past decade, CO2 has been proposed and studied as the working fluid mining low-enthalpy geothermal energy owing to its favorable thermodynamic properties. The purpose of this study is to numerically evaluate the technical feasibility of CO2-circulated geothermal production from depleted oil reservoirs in North Oman, which are usually thin-layered, relatively homogeneous and low-permeable, inclined, compartmentalized, and sealed by faults. A numerical reservoir model is developed to simulate CO2 circulation and heat transfer in a geothermal prospect in North Oman. The reservoir is assumed to have experienced CO2-enhanced oil recovery and was initially flooded by CO2 and residual brine. A triplet horizontal well placement, one central injection well, and two parallel production wells are horizontally placed in the thin-layered reservoir to circulate CO2. Produced thermal energy capacity is quantitatively assessed based on the model simulation. The findings could provide useful guidance for constructing similar closed geothermal reservoir systems in North Oman and worldwide.