Cyclic loading of an idealized clay‐filled fault: comparing hydraulic flow in two clay gouges

Abstract

faulting/fracturing in the same basin will have formed during the depletion of the reservoir. 39Therefore in many geological settings both natural and induced discontinuities will have 40 formed. 41Fluid flow in argillaceous materials, whether through the bulk rock or along discontinuities, 42is closely related to the mechanical state of the caprock. In particular, the role of faults and 43 fractures as potential conduits or barriers to fluid flow is likely to be of critical importance to 44 seal integrity in Carbon Capture and Storage (CCS) sites. In addition, recent studies [Zoback 45 & Gorelick, 2012] and on-going developments relating to induced seismicity [Green, et al. 46 2011] in other industries have also highlighted the importance of a thorough understanding of 47 the potential for, and controls on, fault reactivation behavior. 57Faulted geological settings are complex systems that are borne out of multiple episodes of 58 deformation, in the form of faulting, subsidence and exhumation, and altered stress regimes. 59This means that faults cannot be viewed as static features over geological time. Nor can they 60 be considered static on CO 2 injection time scales, as complex pore-pressure histories and 61 chemical alteration-driven deformation may also have an impact on caprock systems. As 62 such, time is a significant factor in fault sealing. 63On the long time-scales of interest in CCS, cross-reservoir fluid migration may lead to 64 changes in stress-state long after injection ceases. The response of new or previously-sealed 65 discontinuities exposed to these dynamic conditions, may be significant. Noy et al. [2012] 66 demonstrated that pore-pressure perturbations, resulting from the injection of CO 2 , may 67 persist for significant periods (~300 years) after the injection phase. These perturbations are 68 likely to be particularly large in magnitude within the immediate vicinity of injection, but are 69 also demonstrably of concern 'a considerable distance outside the CO 2 footprint at the end of under an elevated pore-pressure condition, (ii) critically oriented faults with the potential for 74 reactivation (as compared to those far from critically stressed), or faulting with the potential 75 for infrequent but significant seismicity. 76Additionally, both near-and far-field discontinuities may be exposed to a range of changing 77 fluid chemistries during the evolution of a storage site, from CO 2 -rich fluids to the migration 78 of brines at the periphery of the pressure pulse. In contrast to reservoir rocks, the 79 phenomenon of clay swelling is of major importance to the sealing behavior of argillaceous 80 cap-rocks [Horseman et al., 2005; Tsang et al., 2005], with the potential to notably affect 81 transmissivity of discontinuities. CO 2 has been shown to markedly impact on the swelling 82 properties of clays [Espinoza & Santamaria, 2012], but there is a paucity of data relating to 83 the impact on shale swelling properties and, in particular, the potential effects for fault 84 seal...

Stress controls on transport properties of the Mercia Mudstone Group: Importance for hydrocarbon depletion and CO2 injection

“…Void ratio, permeability and the elastic moduli are all dependent on effective pressure. Nevertheless, although a substantial body of work exists examining stress path dependency on the material properties of reservoirs (Jones et al, 1986;Holt et al, 1991;Schutjens et al, 2004;Hangx et al, 2013;Lynch et al, 2013;Cuss et al, 2016), there is a limited amount of experimental evidence examining the influence of stress history on caprock behaviour.…”

Experimental Study on Viscoplastic Property of Unsaturated Reticulate Red Clay Used as an Engineered Barrier

“…Some researchers have proposed parameters for describing clay viscoplasticity [14,15]. Some viscoplastic parameters focus on the creep properties of clay [16]; others focus on the loading rate effects of clay [17,18]. A number of researchers [19][20][21][22][23][24][25] have reported the considerable effects of loading rate on soils, through stress-strain experiments conducted in a laboratory.…”