Integrating underground gas storage experience for CCS optimisation

Abstract

Carbon capture and storage (CCS) sites require diligent assessments to account for potential leakage over time. Leakage pathways include both natural and engineered (e.g. wells) invoking the requirement for a structured technical analysis as part of a risk inventory. This paper focuses on lessons learnt from underground gas storage (UGS) sites to guide CCS technical workflows to handle natural geological risk elements. UGS facilities have been operating for over a 100 years. Their injection and withdrawal histories, by their very nature, test the complex changes that occur to the reservoir and cap-rock over time and provide valuable insight to demonstrate the feasibility of CCS and its potential for long-term storage. Geomechanical assessment of the reservoir and cap-rock requires an inventory of core material, log and seismic data with the aim of selecting the appropriate data to model the ability of that formation to contain a column of CO₂. As supercritical CO₂ is injected into the formation and pore pressure builds, the geomechanics of the reservoir needs diligent review to assess the potential to trigger failure on the cap-rock and pre-existing faults and fractures. UGS injection/withdrawal histories assist in the reservoir and overburden static and dynamic modelling along with designing a measurement, monitoring and verification process for CCS sites. Technical workflows, from seismic and static modelling to geomechanics and dynamic simulation and back to seismic for containment monitoring, are discussed that have been refined by UGS experience to benefit the selection of potential CCS sites.