Abstract This paper outlines the CO2 injection strategies proposed for a nearly depleted clastic gas field offshore Peninsular Malaysia, aimed at managing an anticipated CO2 production rate of approximately 5 MTPA over 23 years, as forecasted from future development plans. As part of the feasibility assessment for CO2 injection and storage in this field, the field's ability and capacity to accommodate the incoming CO2 rate must be demonstrated to support further detailed evaluations and decision-making. Comprehensive reservoir modelling studies, combined with analytical evaluation analysis were conducted on multi-stacked reservoir packages which consists of four major and eight minor reservoirs. These assessments aimed to determine the storage capacity range and CO2 injection profiles within the safe operating limits recommended by geomechanical studies. Additionally, the maximum CO2 injection rate per well was set approximately 20% below the critical injection limit, as determined by laboratory experiments on CO2 injectivity, to avoid pore plugging. The study covered 24 years of gas production history matching and followed by 23 years of CO2 injection. Two injection scenarios were developed to manage the forecasted incoming CO2 permeate stream of 5 MTPA over 23 years. Scenario-1 involves CO2 injection and storage in both major and minor reservoirs, requiring an estimated eleven injectors to reach the injection targets. In contrast, Scenario-2 focuses only on major reservoirs, reducing the number of required injectors by half. Although Scenario-1 offer approximately 17% more storage capacity, Scenario-2 is more economically attractive with less injectors further improving project feasibility. Due to the predicted lower average reservoir pressures across all reservoirs at the start of injection and to mitigate risk of flow assurance issues, CO2 will be injected in gaseous phase first to pressurize reservoir pressure above approximately 1,100 psia, after which the injection fluid will transition from gaseous to supercritical CO2/dense phase. However, since neither scenario can sustain the required 5 MTPA injection rate until 2050, as required, hence the inclusion of a secondary storage site is recommended to maintain the plateau injection rate throughout the 23-year period. This paper highlights potential CO2 injection strategies for the aforesaid field. However, the capacity availability from the field alone is insufficient to handle CO2 injection for the full 23-year period, providing important insights for the project team to consider incorporating secondary storage site(s) into the overall storage development plan.
Jalil et al. (Mon,) studied this question.