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.