Integrated 2-Way Fully Coupled Reservoir Dynamic-Geomechanical Modelling Approach for CO2 Storage Risk Assessment in a Malaysian Carbonate Field
Authors: Mustafa M Azlan , M Ali Siti Syareena , Yakup M Hamzi , Tan Chee Phuat 
Published: February 2022

Abstract
A study was conducted on Field M to assess CO2 storage potential and to evaluate the risks and uncertainties based on an integrated dynamic-geomechanics modeling approach. Field M is located at north of Central Luconia Province in Sarawak Basin, Malaysia. Most of the depleted carbonate formation in Sarawak Basin undergone pore collapse at various rates during its production life. In order to consider the impact of pore collapse towards reservoir properties, a seamless coupling simulation approach between dynamic model and geomechanics model is important to generate robust storage capacity and storage containment integrity assessment. The high abandonment pressure, uncertainties caused by reservoir compaction during the production life and subsequent injection period, and the risk of CO2 leakage from the reservoir due to fault re-activation and cap-rock integrity breach by the injection operations are also evaluated. The assessment was undertaken by building the compositional dynamic model that was then history matched in standalone mode to the historical production data with a reasonable quality index. The dynamic model grid was embedded with overburden, underburden and sideburden in the geomechanics model grid, and the reservoir properties and embedment grid properties were then populated in the geomechanics model. This process was followed by another history match in 2-way fully coupled dynamic-geomechanics modeling approach whereby the reservoir production and pressure depletion, and subsidence were matched. Injection simulations were subsequently conducted to assess the impact of reservoir compaction, trapping mechanisms, fault stability and cap-rock integrity towards achieving the maximum injectivity and storage capacity. It was observed that 4.41% of porosity and 12.11% of permeability reduction associated with reservoir compaction occurred during production whilst there was limited reversal in both parameters’ reduction during injection as the rock deformation was largely irreversible plastic deformation. The simulated subsidence was matched with the actual 20-year GPS subsidence measurement data collected at platform location. This history matched 2-way fully coupled model was subsequently used as the base case for simulating the CO2 injection options. The simulations showed that Field M has the potential to store up to 2.3 Tscf until the pressure reaches the cap-rock pressure limit. The simulations also showed that all the faults and cap-rock maintained their integrity and the seabed uplifted by 0.05 ft during the end of injection period. This paper provides a detailed description on CO2 storage site assessment using a 2-way fully coupled dynamic-geomechanics modeling approach in a highly porous carbonate reservoir which addresses trapping mechanisms, fault stability and cap-rock integrity, and their impact on injectivity and storage capacity. The information may be adopted for evaluation of other CO2 storage projects in b oth carbonate and clastic reservoirs worldwide ensuring their safe long-term storage.