CO2-Brine Relative Permeability of HPHT High CO2 Complex Carbonate Rocks: Case Study from Sarawak Basin, Offshore East Malaysia

Abstract A high carbon dioxide (CO2) carbonate gas reservoirs located in East Malaysia's waters (denoted as S Field) was expected to be developed for hydrocarbons production while storing the CO2 separated from the produced CO2-rich hydrocarbons. High challenge was expected to de-risk the subsurface uncertainties of S Field due to its strong heterogeneity, large amount of CO2 initially present in the reservoir and high reservoir temperature conditions. The permeability of targeted injection is low which makes it more complex in term of characteristics. Relative permeability is one of the most important properties influencing the fate and transport of CO2. Generating relative permeability for CO2-brine in this kind of carbonate rocks system possessed a different challenge due to the CO2 solubility, CO2-mineral reactions and low permeability domain. Thus, this study presents three new sets of relative permeability measurement for drainage conducted in low permeability (<10 mD) carbonate samples which is acquired from targeted injection zone is S Field. Unsteady-state method was employed for the experimental analysis and all the measurements were conducted at reservoir conditions. Mineral packed column was installed to mimic the aquifer brine conditions and eliminate the geochemical reactivity during the tests. Two-phase flow simulator was used to history match the data generated from the coreflooding experiments to generate the representative CO2-brine drainage relative permeability curve. Pre- and post-CO2 flooding core characterization, using RCA (Routine Core Analysis), NMR-T2 (Nuclear Magnetic Resonance) and X-Ray CT-scan were conducted to examine any petrophysical alteration that might take place during the experiment. The results from the three conducted tests showed moderate to high end point relative permeability to CO2 (>0.55) and low to moderate irreducible brine saturation (0.01 to 0.4). Except for the lowest permeability sample, the post-CO2 flooding characterization showed minimal impact in term of petrophysical and micro-structural alterations due to the geochemical inhibition by mineral packed column. The lowest permeability sample was observed to be affected by high injection pressure which altered the properties of the core. Based on the generated relative permeability information, the injection of CO2 into the targeted zone is expected to provide better CO2 flow during CO2 injection and large pore-space capacity for CO2 occupancy which serve as a good candidate for CO2 storage.