Experimental study to estimate CO₂ solubility in a high pressure high temperature HPHT reservoir carbonate aquifer

The X field is one of PETRONAS's Research & Development (R&D) initiative plans involving separation of high CO ₂ -Hydrocarbon gas and CO ₂ storage in offshore Malaysia. The X field is a high pressure high temperature (HPHT) carbonate reservoir with a temperature of 423 K and pressure of 36.0 MPa with about 500 m of gas column. It was chosen as a candidate due to its well and reservoir data completeness. The plan is technically challenging as it involves re-injecting produced supercritical CO ₂ back into an aquifer reservoir for permanent storage. Recently acquired X field DST data indicates the presence of CO ₂ in the aquifer, up to a level nearing saturation. Information of the initial CO ₂ concentration level in the aquifer reservoir is critical to ensure the success of the CO ₂ injection. Predictions on this initial CO ₂ solubility have been made using available well data, however the reliability of the results has to be validated by an experimental study. Therefore, an extensive experimental approach to measure initial CO ₂ solubility in the X field aquifer reservoir has been conducted. As pressure, temperature and salinity are the important key parameters that influence CO ₂ solubility, detailed information about X field gas and aquifer brine compositions are well determined prior to the solubility measurement. Utilizing lab facilities at Heriot-Watt University (HWU), measurements were conducted at T=423.15 K and pressure at 36.0 MPa to mimic the X field aquifer conditions. The experimental results obtained are compared against available literature data, Duan Model and sCPA-EoS model and reasonable agreements were observed. Experimental results indicated that the X field aquifer is not fully saturated with CO ₂ and it could accommodate an additional 6 mol% of CO ₂ dissolved in the brine. In addition, approximately 6 mol% of hydrocarbon will be recovered from the same aquifer system as a result of CO ₂ injection due to the CO ₂ -Hydrocarbon displacement. This paper details lab measurements of initial CO ₂ solubility in the X field aquifer, including preparation, experimental procedure, results and discussion as well as suggested future works. Reservoir simulation incorporating the experimental data obtained from this study is necessary and recommended, for getting a full picture of the CO ₂ injection program for the current Carbon Capture Utilization & Storage (CCUS) project.