Openhole Completion Integrity Analysis for Life of CO2 Injector Well

ABSTRACT: A study was conducted to investigate the openhole completion integrity for a CO2 injector well in a Carbon Capture and Storage (CCS) project in offshore Sarawak, Malaysia. A number of completion designs were considered, including openhole completions. Hence, the main objective of this study is to analyse the stability of the openhole section from pre-CO2 injection until end of injection. As part of the project, one-way coupled thermal geomechanics-dynamic modelling was conducted to assess the geomechanical containment risks. Based on the coupled modelling results, significant stress changes are observed at the injector during the injection period due to the effects of injection and CO2 cooling which increased and decreased the stresses, respectively. The stresses, temperatures and pore pressures were then extracted from the coupled model at several key time-steps throughout the injection period and used for openhole stability analysis. Several scenarios were analysed which correspond to the end of drilling, after drilling fluid is displaced with brine prior to injection, and start, intermediate and end of the CO2 injection. Additionally, the stability analysis was also conducted for scenario whereby injection is paused, a scenario which may potentially occur due to operational-related issues. The potential integrity risk of the openhole is determined based on the magnitude of wellbore failures predicted in the analysis. The results of the openhole stability analysis of the injector well throughout CO2 injection showed that minor to considerable shear failures and hydraulic fractures are predicted, in particular during injection stoppages. During the stoppages, the predicted breakouts become more severe at specific sections within the reservoir formation. As there are potential risks of openhole instability during the life of CO2 injection, perforated liner is adopted as the completions for the reservoir interval. Similar analysis is recommended for future CCS projects to ensure the completions method is aligned with the overarching goal of ensuring safe, long-term CO2 storage in the reservoir, protecting both the environment and the integrity of the overall storage project.