Predicting CO2-Brine-Rock Geochemical Interactions in Depleted Clastic Gas Field, Offshore Malaysia

Abstract Field K, which is a depleted clastic field located in offshore Malaysia is identified as one of the storage sites to be developed to sequester the produced CO2 from nearby high CO2 gas field. Understanding the CO2-brine-rock geochemistry aspect is essential in developing any storage sites. Unfortunately, the availability of reliable core samples for the old producing field are typically limited due to its age and poor conditions of the core. This possessed significant challenge to characterize CO2-brine-rock geochemistry comprehensively in Field K. Thus, this research highlights the methodology to populate the geochemical information derived from available core samples to field scale via drill cuttings to de-risk the geochemical impact of the field. Core-flooding experiment was conducted using representative sandstone samples, selected from the target zone. The experiment were conducted by injecting 20 pore volume (PV)/800 minutes of carbonated brine into the composite cores in which the effluents were periodically collected before the samples were left for 14 days of ageing. Porosity, brine permeability and CT-scan analysis were conducted to measure the alteration occurred as a result of geochemical reactions. The effluents information from (20 PV of injection) was used to calibrate the kinetic rate parameters of the reactive transport modelling. The validated kinetic rate parameters were then used to simulate the geochemical impact based on mineralogical map generated from X-ray diffraction (XRD) analysis of the available drill cutting. The geochemical impact was then demonstrated based on the sensitivity analysis using the generated mineralogical map of different reservoir intervals. The petrophysical properties of the core samples showed minimal changes after the core has been exposed with carbonated brine for 14 days which is consistent with the mineralogical data of the collected drill cuttings showing low reactive minerals concentrations. Based on the experimentally calibrated reactive transport modelling, it was deduced that the noticeable evolution of calcium and magnesium were produced predominantly from calcite and dolomite via dissolution mechanism after interaction with carbonic acid. Based on the sensitivity analysis, the validated reactive transport modelling showed that the porosity changes for all the targeted interval post CO2 reaction is in the range of 0.46 to 0.57 porosity unit which suggest minimal geochemical interaction during CO2 injection in Field K.