East Natuna is well known for its humongous natural gas reserves with a high CO₂ content. The high quantity of carbon dioxide requires implementation cutting-edge capture and storage process in its development plan which comes at a high cost. In order to increase the economic feasibility of the area, the impurities are proposed to be utilized CO2 as working fluid further to generate electricity through Enhanced Geothermal System (EGS). Carbon dioxide has been proven to be a better fluid for EGS as it could reach super critical state in much lower pressure and temperature compared to brine water. Sokang Trough Area in East Natuna Basin was selected as a candidate for pilot project due to its favorable geological condition.

Carbon Capture Storage and Utilization (CCSU) especially EGS in sedimentary basin requires a suitable reservoir that fulfills several geological and engineering parameters. Firstly, it should porous enough to store fluid and permeable to flow it. The storage should also be deep enough to retain temperature above 87.98°F and pressure above 1071 psi in order to keep the CO₂ in supercritical phase. Even further, EGS requires a minimum reservoir temperature of ±300°F to be technologically viable. In order to avoid vertical unintended migration, the reservoir should have high water saturation instead of gas saturation. Lastly, the seal should be able to confine the injected CO₂ column within the storage.

Formation evaluation workflow adapted for CCSU was employed in this study. Porosity, water saturation and permeability was estimated through deterministic approach. Formation pressure was calculated using Eaton’s equation. Reservoir temperature was estimated from available well testing data. Storage capacity was estimated for the whole structure with several cases. Considering all those parameters, several suitable reservoirs were able to be delineated in the CCS-1 well that is located within the East Natuna area.