Abstract
Over the last century, the state of stress in the earth’s upper crust has undergone rapid changes because of human activities associated with fluid withdrawal and injection in subsurface formations. The stress dependency of multiphase flow mechanisms in earth materials is a substantial challenge to understand, quantify, and model for many applications in groundwater hydrology, applied geophysics, CO2 subsurface storage, and the wider geoenergy field (e.g., geothermal energy, hydrogen storage, hydrocarbon recovery). Here, we conduct core-scale experiments using N2/water phases to study primary drainage followed by spontaneous imbibition in a carbonate specimen under increasing isotropic effective stress and isothermal conditions. Using X-ray computed micro-tomography images of the unconfined specimen, we introduce a novel coupling approach to reconstruct pore-deformation and simulate multiphase flow inside the deformed pore-space followed by a semi-analytical calculation of spontaneous imbibition. We show that the irreducible water saturation increases while the normalized volume of spontaneously imbibed water into the specimen decreases (46–25%) in response to an increase in effective stress (0–30 MPa), leading to higher residual gas saturations. Furthermore, the imbibition rate decreases with effective stress, which is also predicted by a numerical model, due to a decrease in water relative permeability as the pore-space becomes more confined and tortuous. This fundamental study provides new insights into the physics of multiphase fluid transport, CO2 storage capacity, and recovery of subsurface resources incorporating the impact of poromechanics.
Highlights
Over the last century, the state of stress in the earth’s upper crust has undergone rapid changes because of human activities associated with fluid withdrawal and injection in subsurface formations
We have explored the impact of stress-dependent pore deformation on multiphase flow mechanisms in a carbonate rock sample by conducting a set of isothermal Primary drainage (PD) and Spontaneous imbibition (SI) experiments under a wide range of effective confining stress conditions (0–30 MPa)
We have shown that the irreducible water saturation Swir increases systematically when increasing effective stress (Fig. 3c), while injection pressure was fixed during PD
Summary
The state of stress in the earth’s upper crust has undergone rapid changes because of human activities associated with fluid withdrawal and injection in subsurface formations. Despite the wealth of studies on the environmental impact of effective stress-induced deformation in subsurface formations, the physical influence of pore deformation on PD and SI mechanisms in the unsaturated zones of aquifers, geological formations that are targets for carbon storage, and geothermal or hydrocarbon reservoirs remains unclear. Recent experiments using both pore-scale and core-scale a nalyses[10,11,12,30,31] have featured the stress dependency of relative permeability and capillary pressure in different materials (e.g., carbonates and sandstones). The detrimental impact of effective stress-induced pore deformation on the reserves of depleted groundwater resources or energy recovery from geothermal and hydrocarbon reservoirs is yet to be fully explored
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
