Geomechanical Risks Mitigation for Safe Long Term CO2 Geological Storage
Authors: Tan C. P. , Ali S. S. , Yakup M. H. , Mustafa M. A. , Chidambaram P. , Azahree A. I. , Mazeli A. H. 
Published: September 2022

ABSTRACT:
There are numerous geomechanical challenges and risks associated with CO2 injection and geological storage that are required to be addressed for maintaining seal integrity throughout the injection operation and storage life. The assessment of geomechanical-related challenges and risks to manage CO2 containment and mitigate leakage risks require a coupled geomechanical study that needs to be conducted as part of feasibility evaluation of injecting and storing CO2 in a field. Changes in stresses, rock mechanical and petrophysical properties based on laboratory CO2-rock interaction test data, displacements, strains and deformations are computed by the coupled geomechanical model using data from the reservoir model including pressure, CO2 concentration, water saturation and temperature. Updated petrophysical properties such as permeability and porosity are passed by the geomechanical model back to the reservoir model and used in the next dynamic simulation step. The geomechanical risks mitigation is illustrated through a study conducted on a field which has been selected as a CO2 storage site. The coupled geomechanical modelling assessed CO2 leakage risk associated with fault re-activation, failure of cap rock and interaction of the injected CO2 with cap and reservoir rocks. Recommendations from geomechanical perspective were subsequently developed for the CO2 injection programme and storage operation. The workflow for the comprehensive assessment of geomechanics-related CO2 leakage risk can be adopted for evaluation of other CO2 projects in both carbonate and clastic reservoirs worldwide.

1. INTRODUCTION
There has been increasing global interest in carbon dioxide (CO2) capture and geological storage as it is one of the best alternative methods of produced CO2 disposal to meet net zero carbon emission as countries are committed to the reduction of greenhouse gas emission following their ratification of the Paris Climate Agreement (Baklid et al., 1996, Bissell et al., 2011, Mustafa et al., 2021 and Tewari et al., 2022). However, there are numerous geomechanical challenges and risks associated with CO2 injection and storage in depleted reservoirs, saline aquifers and dry geological structures that are required to be addressed. The key challenges include delineating the geological seal barrier and maintaining the seal integrity throughout the injection operation and storage life. The pressure, CO2 concentration and temperature changes will give rise to changes in stresses, rock mechanical and rock petrophysical properties, and pose risks to fault reactivation, and breach of caprock, completions and casing integrity. Axial loading on completions due to reservoir compaction could cause buckling collapse and/or cement failure (Smith et al., 2011 and Parimal et al., 2021). These processes and mechanisms can be complex and need to be modelled simultaneously as they inter-relate between them. Hence, the assessment of the geomechanical-related risks to manage CO2 containment and mitigate leakage risks require a coupled geomechanical study that needs to be conducted as part of feasibility evaluation of injecting and storing CO2 in a field (Masoudi et al., 2011, Masoudi et al., 2013, Chidambaram et al., 2021 and Mustafa et al., 2022). The coupling can be in the form of one-way and two-way coupled which include porosity and permeability updating. In the case of a depleted reservoir being targeted for CO2 storage, the geomechanical effects associated with past production as well as future CO2 injection must be considered in the coupled geomechanical modelling.