A Comparative Study to Document the Impact of Cyclical Injection Depletion During Hydrogen Storage in Sandstone Reservoirs Using Digital Core Analysis
Authors:   University of Houston, Sarhan Mohamed , Hathon Lori A. ,   University of Houston, Myers Michael T. ,   University of Houston, Arad Alon ,   Automated Analytics
Published: November 2024

Integrating renewable energy into the global energy market requires the development of numerous storage sites for both natural gas and hydrogen. Concerning hydrogen storage, siliciclastic reservoirs represent promising candidates. Risks associated with storage in these reservoirs include mineralogic alteration or geomechanical failure due to the cyclic injection/depletion associated with hydrogen storage. Developing predictive models for these situations with standard core analysis can be challenging. Alternatively, combining pre- and post-test pore scale studies using two-dimensional (2D) and three-dimensional (3D) digital rock imaging and image analysis techniques with geomechanical measurements performed on the same rock volume provides a powerful approach to investigating the impact of cyclic injection/depletion cycles on reservoir properties. This paper will investigate four different clastic sedimentary reservoirs for cyclical hydrogen injection/depletion under a range of reservoir conditions. Three of the tested samples are industry standards: the Castlegate, Boise, and Bentheim Formations. The fourth is a subsurface reservoir, a Miocene sandstone from the Louisiana Gulf of Mexico Shelf province. The measured porosity and permeability for these samples range from 23 to 30% and 600 md to 7 darcies, respectively. Helium will be used as an analog for hydrogen in this study due to its similarity in size to hydrogen and because we focus principally on the physical impact of repeated cycles of injection/depletion on the formation properties. To monitor this impact, a multiscale multidimensional workflow will be deployed. Pretest samples are imaged using micro-computed tomography (CT) to reconstruct pore/grain geometries and used to numerically simulate physical properties. Because CT data cannot distinguish mineralogy or capture pore/matrix features below the image resolution (3 µm), thin sections are cut from each sample after CT imaging for examination using optical and scanning electron microscopy. By coupling the information from these different imaging modalities, using a newly developed tool for multimodal/multidimensional image registration, a more representative digital rock can be obtained for modeling pore structure, fluid transport, and geomechanical response to multiple injection/depletion cycles. The intended workflow is illustrated in Fig. 1. Utilizing 2D-image segmentation, numerous characteristics of the pore and grain systems are characterized using Quantitative Petrographic Interpretation (QPI) software for 2D image analysis. Several 2D measures of porosity characteristics are in good agreement with those obtained using 3D imaging. The thin section is registered with the CT volume, allowing mineralogic information to be incorporated into the analysis. We illustrate 3D/3D alignment as well to document each sandstone’s physical response and to establish the limits of repeated injection/depletion stresses. Porosity, grain size, compaction state (contact % among grains), cement volume and distribution, and framework grain mineralogy are all observed to be strongly related to the ability of sandstone to undergo repetitive injection/depletion cycles without undergoing failure. Combining multiscale multidimensional imaging techniques provides a powerful tool for quantifying petrophysical properties. This results in a better understanding of the physical response of multiple cycles of injection and depletion on reservoir quality and, thereby, storage efficiency.