Influence of shale‐total organic content on CO₂ geo‐storage potential

Abstract

Shale CO2 wettability is a key factor which determines the structural trapping capacity of a caprock. However, the influence of shale‐total organic content (TOC) on wettability (and thus on storage potential) has not been evaluated despite the fact that naturally occurring shale formations can vary dramatically in TOC, and that even minute TOC strongly affects storage capacities and containment security. Thus, there is a serious lack of understanding in terms of how shale, with varying organic content, performs in a CO2 geo‐storage context. We demonstrate here that CO2‐wettability scales with shale‐TOC at storage conditions, and we propose that if TOC is low, shale is suitable as a caprock in conventional structural trapping scenarios, while if TOC is ultrahigh to medium, the shale itself is suitable as a storage medium (via adsorption trapping after CO2 injection through fractured horizontal wells).

Residual Trapping of CO2 in an Oil‐Filled, Oil‐Wet Sandstone Core: Results of Three‐Phase Pore‐Scale Imaging

“…CO 2 geostorage combined with enhanced oil recovery (CO 2 ‐EOR) is an attractive and economic solution for reducing anthropogenic greenhouse gas emissions and mitigating global warming (Cantucci et al, ; Emberley et al, ; Intergovernmental Panel on Climate Change, ). The targeted oil reservoirs, however, are typically oil wet (Cuiec , ), which drastically reduces residual (Al‐Khdheeawi et al, ; Al‐Menhali et al, ; Al‐Menhali & Krevor, ; Chaudhary et al, ; Iglauer, ; Krevor et al, ; Rahman et al, ) and structural (Naylor et al, ; Iglauer, Al‐Yaseri, et al, ; Iglauer, Pentland, & Busch, ; Iglauer, ; Arif et al, ) trapping capacities and significantly accelerates vertical CO 2 migration (Al‐Khdheeawi et al, ), which is detrimental as the injected CO 2 must not leak back to the surface.…”

Carbon Dioxide Utilization and Sequestration in Kerogen Nanopores

“…%), and ultrahigh TOC (>20 wt. %) [24]. Highest CO 2 adsorption capacity is seen in the ultrahigh TOC region, followed by significant adsorption capacity in the high TOC region; the least adsorption capacity is observed at low TOC region.…”

“…The kerogen pores create a sieve for smaller CO 2 molecules, making shales more attractive for CO 2 sequestration unlike methane (CH 4 ) and other gas molecules [18,30]. Thus, shales can adsorb substantial amounts of CO 2 on kerogen as well as fracture surfaces [19,24]. The level maturity of kerogen is measured by the vitrinite reflectance (% Ro), which indicates the onset of oil (0.6-1.0 Ro%), wet gas (<0.80% Ro) and natural gas (>1.4% Ro) generations, respectively [20,21].…”

“…%) regions, the adsorption trapping mechanism onto the kerogen surface prevails and render shale as storage medium in itself. In other words, shales with high TOC tend to be strongly CO 2 -wet, whereas shales with low TOC content exhibit water-wet conditions, with medium TOC in between strongly CO 2 -wet and water-wet conditions [24]. Furthermore, the presence of interlayering clay minerals (illite) in shales also creates a large surface area for adsorption, although the weight of TOC has a much larger influence [25].…”

“…This method is ideal for simulating gas flow in nanoporous kerogen since the continuum flow (Darcy's law) fails due to dominating pore-wall effects at the microscale. LBM stems from the Boltzmann kinetic theory of gases, where fluids are assumed to be made up of a large number of small particles in random motion, which undergo elastic collisions to conserve mass and momentum [19,23,24]. However, the LBM replaces the fluid molecules with fractious particles to reduce the number of possible particles to a handful [28].…”