Assessing CO2 Injection Effects in Depleted Clastic Gas Fields, Offshore Malaysia: A Geochemical Perspective

Summary Evaluation on rock petrophysical properties alteration due to geochemical interactions is important to assess how these changes impacts the CO2 storage performance in targeted zones/formation. This study aimed to characterize and understand the chemical response due to CO2-water-rock interactions in Field X, which is a depleted clastic gas field located in offshore Malaysia. Four core samples acquired from two targeted reservoir unit (D and E zone) in Field X were reacted with carbonated brine in dynamic (20 PV of injection) and static (14 days) environment under simulated in situ reservoir conditions (8.3 MPa and 373.15 K). The petrophysical and structural changes after the core has been exposed with carbonated brine were examined via Routine Core Analysis (RCA) and X-ray CT scan to determine the impact of CO2-water-rock reaction. The RCA results showed that D zone core samples experienced limited reactivity with carbonated brine (<5%), while E zone core samples experienced noticeable change in permeability (∼15 %). The difference of observation between D and E zone is attributed by the differences in initial petrophysical properties of the rock and the findings indicate that CO2 injection in lower permeability zone has higher geochemical risk as compared to higher permeability zone.