Reactive Transport Simulation for CO2 Sequestration in a Depleted Gas Carbonate Reservoir

Summary Depleted gas fields are one of the potential target for CO2 storage given its proven capacity, sealing structures and existing infrastructure that may be suitable to be re-used, hence provide confidence in storage security and potential cost-saving. A carbonate gas field from Sarawak Basin, offshore Malaysia had been in production from 2002 and 2006. The field had reached its targeted recovery factor of about 70% and ready to be abandoned, making it a good candidate for CO2 storage site. Data such as hydrocarbon production history, core and fluid samples are extensively available to conduct the CO2 storage study for this field. The petrophysical properties are very heterogeneous with average porosity of about 30% and permeability ranging from 10 to 300 millidarcy. A reservoir-scale reactive transport simulation was carried out on actual field geometry and incorporating the heterogeneity of reservoir properties. The reservoir-scale simulation was calibrated with a set of coreflood experiments. The aim is to assess the porosity and permeability changes due to CO2 injection in a CO4-CO2-H2O system. Also, to predict the long-term fate of the CO2 over 100 years after injection and the CO2 trapping mechanisms. Effect of temperature on fluid-rock interactions during CO2 injection was also investigated.