The depleted shale reservoirs have shown promising potentials for permanent geological CO2 storage (GCS) either as a caprock or as reservoir storage units. In this study, we experimentally investigated the impact of localized biogeomechanical process on geological CO2 storage in a depleted heterogeneous reservoir, using subsurface samples from Wolfcamp shale formation and a microbial strain. We first obtained the mechanical properties of shale samples using the scratch test method, in addition to the measurement of their initial porosity and permeability. We treated the shale core samples with a bacteria strain at distinct conditions. Further, we obtain the post-treatment mechanical properties and the new porosity and permeability measurements of the microbially-treated shale samples. Finally, we analyzed the effect of the modified properties on long-term CO2 storage in the Wolfcamp shale formation. Our results indicated that in depleted Wolfcamp shale reservoirs, microbially-altered properties could decrease the porosity, and enhance long-term caprock integrity and the security of stored CO2.

1 Introduction

Biogeomechanics is the scientific study of how biological processes influence the mechanical properties and behavior of rock and soil (Kolawole et al., 2021). Few studies have attempted to investigate the effect of biological processes on the geochemical (Abdel Aal et al., 2004; Atekwana et al., 2006), physical and mechanical properties of unconsolidated sandstones (Kalish et al., 1964; Phillips et al., 2015; Hudyma et al., 2018), carbonates (Raleigh and Flock, 1965), and minerals (Mueller and Défago, 2006).

The bacterium Sporosarcina pasteurii (ATCC® 11859) (Yoon et al., 2001), also known as Bacillus pasteurii, was utilized for this study. The bacterium Sporosarcina pasteurii, was observed to rapidly precipitate calcite in sand columns as the bacteria growth increases, for selective cementation and plugging of porous media (Stocks-Fischer et al., 1999).

Shale reservoirs, with ultra-low permeability, require reservoir-stimulation techniques to inject or extract fluids from the shale reservoirs (Jia et al., 2019; Schwartz et al., 2019; Kolawole et al., 2020; Kolawole and Ispas, 2020a). The clay particle orientation, heterogenous layering, and microfissures are causes of high anisotropy in shale rocks (Hornby et al., 1993). Studies have shown that shale reservoirs have promising potentials for permanent geological CO2 storage (GCS) (Kang et al., 2011; Aljamaan et al., 2017; Kim et al., 2017; Azenkeng et al., 2020; Goodman et al., 2020).

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