Stability of CO2–brine immiscible displacement

Abstract

a b s t r a c tThe viscous stability of the primary drainage process is of major interest for the injection of carbon dioxide (CO 2 ) in saline aquifers, since it determines the spread of the CO 2 plume in the target aquifer and consequently the initial utilization of the pore space for CO 2 storage. In order to analyze the stability of the displacement process, the relative permeability saturation functions must be known; these are usually derived by experiments under conditions representative for the field. It is therefore very important to characterize the flood front stability, not only on the field scale but also on the experimental scale, in order to judge the validity of the experimental results as a precondition for reliable field simulations.Here we investigate the onset of viscous fingering, thereby studying under what conditions CO 2 -brine displacement remains stable. We discuss the role of relative permeability and the stabilizing effect of capillary pressure at different length scales by means of numerical simulations. The results allow us to assess different definitions of the mobility ratio and establish criteria for judging the stability of the displacement process. We further show that in cases where gravitational forces are important, the gravity tongue dominates the fingering pattern, and unstable situations can occur where stability would be predicted, by considering viscous and capillary forces only.In the literature various criteria for the onset of instability have been proposed, but these are inconsistent or inconclusive. Our intention is to bring order into this discussion. In the present study we validate or refute stability criteria by numerical modeling and show that the shock-front mobility ratio correctly describes the onset of fingering. The application of our findings is not limited to CO 2 -brine displacement. The criteria for stability can be applied to most two-phase flow problems in reservoir engineering in general ranging from water flooding to low interfacial tension surfactant flooding.

Use of low- and high-IFT fluid systems in experimental and numerical modelling of systems that mimic CO2 storage in deep saline formations

“…For a given fluid system only permeability (k) and injection rate (q) were varied and all the other parameters were kept constant. The flow velocities observed in experiments were within the range of 0.26-1.29 m/day which corresponds to the flow velocities observed during CO2 storage processes in real reservoirs (Berg and Ott 2012). In order to represent flow in an open reservoir, the outlets located at the edges of the model were open during the experiments and thus injected fluid could displace the brine in all directions available in the 2D-model.…”

Adaptive Mesh Optimization for Simulation of Immiscible Viscous Fingering

“…Daripa and Pasa (2008) studied instability of immiscible displacement in the presence of capillary pressure and showed that the slowdown of instability by capillarity is commonly very rapid. Berg and Ott (2012) studied the stabilizing influence of capillary pressure using a finite volume method and triggered fingers by superimposing a permeability variation on the domain. Jauré et al (2014) have developed a higher order simulator based on the multipoint flux approximation that is readily parallelizable and applied this to the modeling of the experiments described by Riaz et al (2007).…”

Hydrodynamic Fingering Instability Induced by a Precipitation Reaction

“…The reverse case of precipitation is not expected to destabilize an interface as the related decrease in permeability and, hence, in mobility behind the front is expected to block the flow rather than destabilize it. There is, however, increased interest to understand the effect of precipitation reactions during flow displacements in porous media in the context of CO 2 sequestration techniques [11][12][13][14]. Mineralization by which CO 2 injected in a porous medium could undergo precipitation reactions (to yield carbonates, for instance [13][14][15][16]) is indeed promising in view of a permanent safe storage of CO 2 in geological strata.…”

“…Mineralization by which CO 2 injected in a porous medium could undergo precipitation reactions (to yield carbonates, for instance [13][14][15][16]) is indeed promising in view of a permanent safe storage of CO 2 in geological strata. Understanding the conditions in which precipitations can affect the stability of the spreading CO 2 plumes [12] is, thus, particularly important.…”