Quantitative Laboratory Assessment of Caprock Integrity for Geological Carbon and Hydrogen Storage

Abstract

Caprock integrity is a critical factor in geological carbon storage (GCS) and hydrogen storage (GHS), as it ensures containment assurance, environmental and safety considerations, storage efficiency, risk mitigation, long-term viability, public and regulatory confidence, economic considerations, and informed decision-making. Caprock can break mechanically by radial cracking, plastic deformation, inner and outrebounding, and channeling. Understanding these failure mechanisms is crucial, but traditional deformation tracking methods have limitations. To address this gap, this study utilizes three-dimensional digital image correlation (3D-DIC) to investigate the deformation and failure of caprock specimens from GCS and GHS, thereby ensuring their integrity. Caprock samples were compressed diametrically using a precision 100 kN electromechanical load frame moving at 0.05 mm/min. There were a variety of minerals in the samples that were examined. During the diametrical compression testing, a 3D-DIC system was set up to monitor the samples without touching them at a rate of 10 frames per second. A black-and-white speckle pattern is applied to the specimen to monitor its deformation under stress. The 3D-DIC system is used to process, visualize, and analyze caprock sample damage under varied load conditions. A load-strain relationship was established by integrating several factors: 1) DIC-generated horizontal, vertical, and shear strain maps, providing insight into the sequence of strain development and fracture occurrences attributed to pre-existing or natural fractures, anisotropy, heterogeneity, laminations, faults, cracks, or channeling. 2) The results demonstrated a 4-stage deformation evolution process: initial, linear elastic, elastic-plastic, and plastic damage. 3) Additionally, the study illustrated the failure process of caprock samples, yielding tension and compression within ±0.05%, shear within ±0.001%, and a tension-compression ratio ranging from 1% to 5%. 4) three failure patterns were observed in the tested caprock specimens, including central, deviated from the center, and mixed modes due to tension, compression, and shear. Injecting H2 or CO2 into the formation can lead to increased pore pressure and caprock failure in geological carbon and hydrogen storage projects. Geomechanical risks such as caprock instability, fault slip, and formation deformation can occur throughout the project's lifespan. There is no perfect methodology that covers all the problems in caprock integrity research. This study focuses on predicting caprock deformation and failure using non-contact optical methods, with 3D-DIC being more effective in terms of test range, affordability, accuracy, and full-field monitoring. The image-based algorithm is better at understanding anisotropic and heterogeneous conditions, enhancing the inspection of caprock integrity in underground carbon and hydrogen storage projects.