A Toolkit Approach for Carbon Capture and Storage in Offshore Depleted Gas Field

Abstract

Fossil fuels are considered a dependable, cost-effective, and efficient energy source and their utilization has resulted in tremendous growth for humanity. However, it has its downside also. Experts are of the view that present energy systems are unsustainable due to their detrimental impacts on the environment. Oil and gas producers are charged that their infrastructure, utilization of materials and technologies for exploration, development, and operation, and production and consumption based GHG emission is harming the environment severely. Current atmospheric CO₂ concentrations are slightly more than 400 ppm, almost double since the beginning of the industrial revolution. CO₂ concentration is continuously increasing in the atmosphere which is causing an increase in the atmospheric temperature. Studies suggest that if no new emissions occur, even though the temperature would be 1.1°C higher at the end of the century due to significant accumulated CO₂ in the atmosphere. Is opined by some experts that a further increase of CO₂ concentration in the atmosphere would saturate its impact in terms of increasing trend of temperature rather it would be logarithmic in nature which means additional CO₂ concentration in the atmosphere would not increase the temperature alarmingly. However, IPCC suggested that the relationship is more linear and if CO₂ emission is not controlled then its effect would not just be worse but speed up the detrimental effects. Various measures are being taken up to reduce the CO₂ concentration in the atmosphere for preventing major climate change and control the detrimental side effects like natural calamities such as drought, flood, forest fires, and acidification of the ocean. CO₂ Capture and Storage (CCS) is one of the most important efforts in the spectrum of measures being considered and applied for managing this menace and meeting the net zero CO₂ emission target set by countries and companies by 2050. Development and adoption of renewable energy are gaining momentum, but it will take some time before renewable energy plays a dominant role in the total energy mix. Natural gas will play a transition fuel role before achieving the dominant role of renewable energy in the total energy mix and CCS will enable the development of contaminated gas fields to meet the gas demand. The world focus is on renewable and environment-friendly energy development e.g., solar, wind and hydrogen, etc. Carbon dioxide (CO₂) capture, utilization, and storage is the best option for mitigating atmospheric emissions of CO₂ and thereby controlling the greenhouse gas concentrations in the atmosphere. Despite the benefits, there have been a limited number of projects solely for CO₂ sequestration being implemented. The industry is well-versed in gas injection in reservoir formation for pressure maintenance and improving oil recovery. However, there are striking differences between the injection of CO₂ into depleted hydrocarbon reservoirs and the engineered storage of CO₂. The differences and challenges are compounded when the storage site is karstified carbonate in offshore and bulk storage volume. It is paramount to know upfront that CO₂ can be stored at a potential storage site and demonstrate that the site can meet the required storage performance safety criteria. Comprehensive screening for site selection has been carried out for suitable CO₂ storage sites in offshore Sarawak, Malaysia using geographical, geological, geophysical, geomechanical, and reservoir engineering data and techniques for evaluating storage volume, container architecture, pressure, and temperature conditions. The site-specific input data are integrated into static and dynamic models for characterization and generating performance scenarios of the site. In addition, the geochemical interaction of CO₂ with reservoir rock has been studied to understand possible changes that may occur during/after injection and their impact on injection processes/mechanisms. Novel 3-way coupled modeling of dynamic-geochemistry-geomechanics processes was carried out to study long-term dynamic behavior and the fate of CO₂ in the formation. The 3-way coupled modeling helped to understand the likely state of the injectant in the future and the storage mechanism, i.e., structural, solubility, residual, and mineralized trapping. It also provided realistic storage capacity estimation, incorporating reservoir compaction and porosity/permeability changes. The study indicates deficient localized plastic shear strain in overburden flank fault whilst all the other flaws remained stable. The potential threat of leakage is minimal as the target injection pressure is set at initial reservoir pressure, which is much lower than cap rock breaching pressure during injection. Furthermore, it was found that the geochemical reaction impact is shallow and localized at the top of the reservoir, making the storage safe in the long term. The integrity of existing wells was evaluated for potential leakage and planned for a proper mitigation plan. Comprehensive Measurement, Monitoring, and Verification (MMV) were also designed using state-of-art tools and dynamic simulation results. The understanding gaps are closed with additional technical work to improve technologies application and decrease uncertainties. A comprehensive study for offshore CO₂ storage projects identifying critical impacting elements is crucial for the estimation, injection, containment, and monitoring of CO₂ plumes. The information and workflow may be adopted to evaluate other CO₂ projects in both carbonate and clastic reservoirs for long-term problem-free storage of greenhouse gas worldwide.