Well Integrity Study for Carbon Dioxide Injection Well Conversion with High Geothermal Profile at Depleted Gas GX Field, South Sumatra Area

Abstract The newly SX Gas Field, with a CO2 composition ranging between 30-40% are being developed. To minimize the environmental impact of carbon emissions, the company plans to utilize existing mature fields as CO2 storage. GX Field has been identified as a suitable candidate with recovery factor greater than 90%, indication it is currently entering the late phase of production with remaining reservoir pressure of 300 psi. Based on subsurface simulations, the existing production layer in the GX Field could be repurposed for CO2 geologic sequestration site, accommodating cumulative storage 11 to 15 million tonnes (MT) of CO2 at 70% initial pressure, injected above gas-water contact. This study comprises a comprehensive evaluation of casing and tubing integrity under simulated load cases, material selection based on literature review, and a long-term leak risk assessment utilizing Open IAM to project well integrity over a 100-year post injection period. A key challenge addressed is the high geothermal gradient prevalent in the South Sumatra Basin, which introduces complex cyclic loading conditions on the well structural integrity. The findings of this study reveal that the existing well infrastructure in the GX Field, even with a 20% derating to account for 30 years of service, does not meet the required design factors for sustained CO2 injection. Concerns regarding cyclic loading on the Buttress Thread Connection (BTC) of the casing and its potential impact on cement stress in the production section further support this conclusion. Consequently, this study recommends the drilling of a new well specifically designed for prolonged CO2 injection service. This paper will further explore critical aspects including a detailed well integrity assessment of the existing well, leak risk assessment, flow assurance considerations, material selection criteria for the injection environment, a conceptual new well design, and a preliminary plug and abandonment (P&A) strategy for the repurposed injection well.