Gravity currents of carbon dioxide with residual gas trapping in a two-layered porous medium

Abstract

In the geological sequestration of carbon dioxide (CO2), residual gas trapping plays an important role in immobilizing CO2. In this study, we investigate the propagation of gravity currents with residual gas trapping in a two-layered porous medium. We first formulate a model for a constant-flux release of a relatively less dense fluid (CO2) from a point source into a porous medium bounded above by a horizontal less-permeable seal. After a constant-flux release ceases, a fraction of the released fluid remains within the porous spaces at the trailing edge because of the capillary forces. This capillary retention is formulated in a model of gravity currents of a finite-volume release in the two-layered medium. In the latter model, the plume shape at the end of the constant-flux release is used as an initial profile. Using these models sequentially, the propagation of both cross-sectional and axisymmetric currents is quantitatively examined.

Isolated buoyant convection in a two-layered porous medium with an inclined permeability jump

“…Consistent with figure 2, it can be shown that for draining lengths significantly greater than the gravity current height, the direction of remains vertical and its length is given as . Taking these factors into consideration, the draining velocity can be written as In the limiting case when , (2.8) reverts back to the expression used in previous works (Goda & Sato 2011; Sahu & Flynn 2017).…”

“…. (ii) The upper and lower layers are assumed to be very deep in vertical extent (Goda & Sato 2011); the consequences of assuming otherwise will be briefly highlighted in § 4. (iii) Initially, the entire porous medium is assumed to be uniformly saturated with ambient fluid of density .…”

“…In the latter case, Pritchard, Woods & Hogg (2001), Neufeld & Huppert (2009) and Farcas & Woods (2009) studied the flow of a gravity current over a thin permeable layer. The extension to the thick lower layer case has been explored by Goda & Sato (2011) and Sahu & Flynn (2017) among others. Whatever the lower layer thickness, the draining flow from the underside of the gravity current has been modelled by considering the flow to be driven by the hydrostatic head of the overlying gravity current (Acton, Huppert & Worster 2001; Pritchard et al 2001; Goda & Sato 2011).…”

“…The extension to the thick lower layer case has been explored by Goda & Sato (2011) and Sahu & Flynn (2017) among others. Whatever the lower layer thickness, the draining flow from the underside of the gravity current has been modelled by considering the flow to be driven by the hydrostatic head of the overlying gravity current (Acton, Huppert & Worster 2001; Pritchard et al 2001; Goda & Sato 2011). In case of a thick lower layer, the source fluid is pulled both along and across the interface between the two layers, which we call the permeability jump, and the gravity current ultimately reaches a terminal or run-out length.…”

Dispersive entrainment into gravity currents in porous media

“…For example, gravity currents on an inclined surface have been studied by Vella & Huppert (2006) and Gunn & Woods (2011), or in a vertically confined medium by Nordbotten, Celia & Bachu (2005), MacMinn et al (2012), Pegler, Huppert & Neufeld (2014) and Zheng et al (2015). Moreover, by relaxing the restriction of a homogeneous medium, Pritchard, Woods & Hogg (2001), Goda & Sato (2011) and Sahu & Flynn (2017) have investigated gravity currents in layered porous media of differing permeabilities, while Zheng, Christov & Stone (2014) have investigated flow in horizontally heterogeneous medium. Formulations for modelling gravity currents in a highly heterogeneous medium have been presented by Anderson, McLaughlin & Miller (2003, 2004, who describe homogenization methods for the averaging of medium properties.…”