Optimising the CO2 Storage Potential in Deep Saline Aquifer by Creating Pressure Sink

Abstract

Abstract Malaysia has pledged to reduce the intensity of Green House Gas (GHG) emission by 45% based on Gross Production Product (GDP) in 2030 and ultimately net-zero carbon emission in 2050 during UNFCCC-COP 26 in Scotland. However, the growing energy demands need some of the high contaminant (CO2) natural gas fields in the region to be developed. To mitigate the negative climatic impact of such developments and manage the huge quantities of produced CO2, Carbon Capture and Storage (CCS) is the only viable technology in the current world. In this paper, a multidisciplinary subsurface study is conducted to unlock the potential containment for CO2 storage and estimate the effective volume in deep saline aquifer. A fit for purpose 3D geological model was built for K reservoir in Z field. A range of porosity was tabulated from well log data and permeability was estimated from available poro-perm cross plot. Then, a compositional dynamic model with appropriate CO2 storage features is established using CMG-GEM simulator. The initial formation pressure and temperature were estimated from available well tests, and PVT and SCAL data are considered from an analogue field. The base case model was initialized, and several scenarios were run to estimate the optimum effective CO2 storage capacity for injection period of 25 years. The CO2 gas injection started on the January 2025 with 60 MMscf/d injection rate and maximum water withdrawal was set at 30 kbbl/d. The prediction ran until 2050. An effective CO2 storage capacity for non-voidage case is estimated at 4.9 Bscf for a commingled injector with no producer case. This contributed only 3% of the theoretical storage capacity that can be sequestered due to high pressure build-up in the reservoir. For voidage case, one injector and one producer (commingled) case predicted to effectively sequestered 80.13 Bscf, which is approximately 51% of the total theoretical storage capacity. The simulation was further optimized with two injector and one producer (commingled) case where a total of 95.44 Bscf gas is predicted to be sequestered in the reservoir. This contributed to the highest effective CO2 storage volume, approximately at 61% of the total theoretical storage capacity. This study presents the feasibility and optimization of CO2 sequestration in saline aquifer zone for one of Malaysia pre-development fields that can be as part of forecasting the CO2 injectivity and behaviour in storage reservoir during containment. Based on the study outcomes, it was well understood that the small, restricted saline aquifers may not present the greatest avenue for sustainable and economic CO2 sequestration due to their limited size and the requirement of water production to create additional voidage/pressure sink. In such a scenario, extensive and open aquifer systems in the region may be analyzed for their containment integrity and effective storage capacities.