CO2 Storage Assessment in a Malaysian Depleted Carbonate Reservoir With 2-Way Fully Coupled Dynamic-Geomechanics Modeling for Safe Long-Term Storage

This paper describes the study of the first field in Malaysia for Carbon Capture and Storage (CCS) deployment by PETRONAS. PETRONAS has the ambition to make Malaysia a regional carbon storage hub and with that in mind, has the strategic plan for CCS deployment across the depleted gas fields in Malaysia with an estimate of 46 trillion cubic feet of storage volume in total. Sarawak Basin, Malaysia has a large numbers of hydrocarbon fields with high CO2 content which are yet to be developed. CCS is required for developing these high CO2 fields to be in line with net zero carbon direction of PETRONAS. After initial screening and risk management assessment, some of the depleted carbonate fields in the region are considered for the next phase of study related to the deployment of CO2 storage. The field discussed in this paper is believed to have common strong aquifer with neighbouring fields and has a highly heterogeneous reservoir. It also has anumber of extensive and localized baffles/barriers together with highly karstified areas, resulting in significant variations of reservoir characteristics and hence, dramatically affect the flow behaviour in the reservoir, in terms of pressure and water breakthrough. With its high porosity and permeability properties, high compaction and subsidence resulted from pore collapse phenomenon was observed in the reservoir and seabed, respectively. These behaviours need to be captured accurately during the CCS assessment for a reliable estimation of hydrocarbon in place, hydrocarbon interval and aquifer pressures, reservoir compaction, seabed subsidence and hence, the CO2 storage capacity. Dynamic reservoir simulation coupled with geomechanical modelling was used in the study to accurately predict the reservoir and overburden behaviours in the complex reservoir which was necessary for the CO2 storage capacity assessment. In the 2-way fully coupled dynamic-geomechanics modelling, geomechanical analysis is conducted to evaluate the field behaviour including reservoir compaction, seabed subsidence, fault stability and caprock integrity. With the change in the pressure and temperature, either by production or injection, the reservoir stress will change with associated deformation which in turn change the porosity and permeability which will subsequently impact the new pressure distribution and corresponding compaction and subsidence. In addition, the stress changes could result in fault reactivation and caprock integrity breach. Due to the interaction, the stress state was[WT1] updated by coupling the effects of geomechanics on reservoir simulation, so that the compaction and stress changes in the field can be honoured to accurately match the seabed subsidence and reservoir pressure distribution. These enable robust prediction of the storage capacity of the reservoir as well as field integrity. The 2-way fully coupled dynamic-geomechanics study results drive key decisions in the planning of the CCS strategy development and provide answers related to caprock integrity, fault stability, reservoir injection pressure upper limit, storage capacity, long term fluid containment and monitoring program to mitigate potential geological leakage in the long term. The results of this pioneering CCS study which is the first of its kind in Malaysia are presented and discussed.