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The Tangguh gas development project, contributing about one-third of Indonesia's national gas production, is advancing with an Enhanced Gas Recovery (EGR) initiative. This project aims to reinject produced CO₂ back into the subsurface with the dual objectives of reducing CO2 emissions and improving gas recovery through pressure maintenance and gas displacement. This paper presents the Tangguh EGR development plan, which co-optimizes recovery improvement and CO2 sequestration under the wide range of subsurface uncertainties.

The methodology involved comprehensive site characterization of the Upper Roabiba sand formation of Vorwata, evaluating storage capacity, injectivity, and containment potential for CO₂ injection and storage. Dynamic reservoir models were built to simulate EGR performance under known subsurface descriptions. Sensitivity analysis tested relevant subsurface uncertainties, while ensemble modeling explored the uncertainty space to produce a set of calibrated models representing the range of EGR outcomes. Optimization techniques evaluated various injection arrangements to identify the optimum configuration for a robust EGR development plan.

Site characterization demonstrated that the Upper Roabiba sand formation of Vorwata exhibits favorable characteristics for commercial EGR and CCS operations. Sensitivity analysis identified reservoir thickness, structure, and trapped gas saturation as key subsurface uncertainties impacting EGR performance. In all tested cases, EGR consistently demonstrated the potential to enhance gas recovery by 0.5% to 3.2% and sequester up to 88% of the injected CO2. Sequestration is limited by the cessation of EGR operations at the onset of LNG plant turndown, with the remaining injected CO2 re-produced and transported alongside field gas to the sales point, assuming an available pipeline gas market. The southwest gas leg was preferred for CO2 injection, with three injection wells deemed optimum for delivering CO2 at the targeted rates.