Efficiently engineering pore-scale processes: The role of force dominance and topology during nonwetting phase trapping in porous media

Abstract

a b s t r a c tWe investigate trapping of a nonwetting (NW) phase, air, within Bentheimer sandstone cores during drainage-imbibition flow experiments, as quantified on a three dimensional (3D) pore-scale basis via x-ray computed microtomography (X-ray CMT). The wetting (W) fluid in these experiments was deionized water doped with potassium iodide (1:6 by weight). We interpret these experiments based on the capillary-viscosity-gravity force dominance exhibited by the Bentheimer-air-brine system and compare to a wide range of previous drainage-imbibition experiments in different media and with different fluids. From this analysis, we conclude that viscous and capillary forces dominate in the Bentheimer-air-brine system as well as in the Bentheimer-supercritical CO 2 -brine system. In addition, we further develop the relationship between initial (post-drainage) NW phase connectivity and residual (post-imbibition) trapped NW phase saturation, while also taking into account initial NW phase saturation and imbibition capillary number. We quantify NW phase connectivity via a topological measure as well as by a statistical percolation metric. These metrics are evaluated for their utility and appropriateness in quantifying NW phase connectivity within porous media. Here, we find that there is a linear relationship between initial NW phase connectivity (as quantified by the normalized Euler number,v) and capillary trapping efficiency; for a given imbibition capillary number, capillary trapping efficiency (residual NW phase saturation normalized by initial NW phase saturation) can decrease by up to 60% as initial NW phase connectivity increases from low connectivity (v % 0) to very high connectivity (v % 1). We propose that multiphase fluid-porous medium systems can be efficiently engineered to achieve a desired residual state (optimal NW phase saturation) by considering the dominant forces at play in the system along with the impacts of NW phase topology within the porous media, and we illustrate these concepts by considering supercritical CO 2 sequestration scenarios.

Enhancing residual trapping of supercritical CO2 via cyclic injections

“…Results from reservoir condition core-scale experiments consisting of three D-I cycles indicate that although measured pressure profiles and relative permeability are cycle dependent parameters, cycle number has no discernible impact on residual scCO 2 saturations [Saeedi et al, 2011]; a similar result was found by Li et al [2015], who measured initial-residual saturation levels over two D-I cycles in Berea sandstone and found that the results conformed to the expected monotonic trapping curve. In contrast, results from recent pore-scale studies have suggested that intermittent injection patterns, or cyclic injections similar to water-alternating-gas schemes, could be utilized to break up the scCO 2 plume and enhance residual trapping of scCO 2 [Herring et al, 2013[Herring et al, , 2015; cyclic injection schemes have also previously been suggested by researchers performing basin-scale simulations [Spiteri et al, 2005]. In contrast, results from recent pore-scale studies have suggested that intermittent injection patterns, or cyclic injections similar to water-alternating-gas schemes, could be utilized to break up the scCO 2 plume and enhance residual trapping of scCO 2 [Herring et al, 2013[Herring et al, , 2015; cyclic injection schemes have also previously been suggested by researchers performing basin-scale simulations [Spiteri et al, 2005].…”

Modelling capillary trapping using finite-volume simulation of two-phase flow directly on micro-CT images

“…At the pore scale, micro-CT technology has the capability to image the location of the residual phases inside the pore space, thus providing detailed information on the size and shape of the residual ganglia [17][18][19][20][21][22][23][24][25][26][27][28]. Another important application of the micro-CT imaging is the measurement of contact angle at reservoir conditions (elevated temperature and pressure) [29], which is one of the main input parameters for pore-scale numerical modelling.…”

Subphase Approach to Model Hysteretic Two-Phase Flow in Porous Media

“…In order to devise models applicable to a range of capillary numbers, additional parameters describing the topology of the fluid subphases may be crucial. The topology of a fluid subphase can be described by the Euler characteristic, which has been used previously by Herring et al (2015) to study the 3D topology of the nonwetting fluid phase and its effect on nonwetting phase trapping. They found that for high capillary numbers, the nonwetting phase Euler number plays an important role on the residual nonwetting saturation.…”