Impact of relative permeability hysteresis on geological CO₂ storage

Abstract

[1] Relative permeabilities are the key descriptors in classical formulations of multiphase flow in porous media. Experimental evidence and an analysis of pore-scale physics demonstrate conclusively that relative permeabilities are not single functions of fluid saturations and that they display strong hysteresis effects. In this paper, we evaluate the relevance of relative permeability hysteresis when modeling geological CO 2 sequestration processes. Here we concentrate on CO 2 injection in saline aquifers. In this setting the CO 2 is the nonwetting phase, and capillary trapping of the CO 2 is an essential mechanism after the injection phase during the lateral and upward migration of the CO 2 plume. We demonstrate the importance of accounting for CO 2 trapping in the relative permeability model for predicting the distribution and mobility of CO 2 in the formation. We conclude that modeling of relative permeability hysteresis is required to assess accurately the amount of CO 2 that is immobilized by capillary trapping and therefore is not available to leak. We also demonstrate how the mechanism of capillary trapping can be exploited (e.g., by controlling the injection rate or alternating water and CO 2 injection) to improve the overall effectiveness of the injection project.

Lifetime of carbon capture and storage as a climate-change mitigation technology

“…Trapping occurs primarily after injection, when the CO 2 migrates due to the aquifer slope and the natural head gradient. As the buoyant plume of mobile CO 2 (dark gray) rises and spreads away from the well array, residual trapping immobilizes blobs of CO 2 in its wake (light gray) (19,29,30), and solubility trapping shrinks the plume from below (blue) (20, 21).…”

“…Although trapping can be analyzed over a wide range of length scales, we consider trapping at the large scale of an entire geologic basin because large volumes of CO 2 will need to be stored to offset emissions (3). We consider residual trapping, in which blobs of CO 2 become immobilized by capillary forces (19), and solubility trapping, in which CO 2 dissolves into the groundwater (20,21), because these mechanisms operate over relatively short timescales and provide secure forms of storage ( Fig. 1 A and B).…”

Direct Measurement of Static and Dynamic Contact Angles Using a Random Micromodel Considering Geological CO2 Sequestration

“…This is due to the following two facts: (1) contact angle hysteresis (the difference between ACA and RCA) influences the relative permeability, implying that factors affecting contact angle hysteresis such as pressure, and pore throat size should be considered to select the relative permeability in numerical simulation; and (2) the presence of trapped nonwetting phase (CO2) influences the flow path of wetting fluid (water). When trapped non-wetting phase (CO2) occupies larger pores, it causes the injected wetting fluid (water) to change its flow paths, resulting in decreased relative permeability [56]. Spiteri et al [57] have performed numerical modelling of a Water Alternating Gas (WAG) system for CO2 sequestration and shown favorable results for residual trapping due to relative permeability hysteresis by decreasing leakage risk through lowering the accumulation of CO2 plum under caprock.…”

Large-scale Invasion Percolation with Trapping for Upscaling Capillary-Controlled Darcy-scale Flow

“…We refer in this paper to the wetting phase as water and the non-wetting phase as oil, although the process is applicable to any pairs of immiscible fluids, including CO 2 -brine systems where large-scale trapping is extremely important for storage security (Saadatpoor et al 2010;Juanes et al 2006). …”