Enhanced Gas Condensate Recovery by CO2 Injection in Low Carbon World

Abstract

Abstract CO2 injection in gas condensate reservoirs has the potential to enhance gas recovery while reducing CO2 emissions, aligning with Petroleum Development Oman’s (PDO) goal of decreasing greenhouse gas intensity and producing low-carbon oil. PDO has a rich portfolio of gas condensate reservoirs, which could be good candidates for the injection of captured CO2. However, finding the best candidate for CO2 injection may be a challenge given the diversity of the portfolio. The focus of this paper is to explore key mechanisms of CO2 injection in gas condensate reservoirs to enable the selection of the most economically attractive candidates and understand the key factors that can impact the economics of an enhanced gas condensate recovery (EGCR) project. Conceptual and full-field simulation models were developed to estimate the potential incremental recovery and the amount of retained CO2 during the production phase of the project, allowing for the estimation of the net gas utilization factor. One-dimensional conceptual models were employed to reveal the predominant mechanisms and net gas utilization (NGU) for different scenarios, varying the depletion state of the reservoir, condensate-to-gas ratio (CGR), and injection rate. Additionally, two field examples are presented to demonstrate the expected NGU and suggest strategies for improving CO2 utilization. The results of this study demonstrate the high potential of CO2 injection to maximize the recovery of gas condensate. In addition, this study demonstrates the importance of the miscible displacement of condensate by CO2 for depleted reservoirs over revaporization, which requires higher pressure than miscible displacement and hence higher amount of CO2. The results suggest that CO2 injection in less depleted gas condensate reservoirs at the start of CO2 injection can be more economically attractive than in depleted reservoirs due to the better net gas utilization (NGU) of CO2. For highly depleted reservoirs, higher injection rates are required to increase pressure, resulting in poor NGU compared to less depleted reservoirs. The study also highlights the importance of optimizing injection rates and/or injection durations to maximize oil production per ton of injected CO2. In conclusion, while CO2 injection presents significant opportunities for enhancing gas condensate recovery and CO2 storage, the economics of such projects are contingent upon improving NGU and ensuring the cost-effectiveness of CO2 capture, transport, and injection compared to oil revenue.