Wettability Evaluation of a CO₂/Water/Bentheimer Sandstone System: Contact Angle, Dissolution, and Bubble Size

Abstract

The success of CO 2 storage in deep saline aquifers and depleted oil and gas reservoirs is largely controlled by interfacial phenomena among fluid phases and rock pore spaces. Particularly, the wettability of the rock matrix has a strong effect on capillary pressure, relative permeability, and the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. Precise understanding of wettability behavior is therefore fundamental when injecting CO 2 into geological formations to sequestrate CO 2 and/or to enhance gas/oil production. In this study, the contact angles of Bentheimer sandstone/water/CO 2 or flue gas have been evaluated experimentally using the captive-bubble technique in the pressure range from 0.2 to 15 MPa. The experiments were conducted using different compositions of aqueous phase with respect to CO 2 , i.e., unsaturated and fully saturated. It has been shown that a reliable contact-angle determination needs to be conducted using a pre-equilibrated aqueous phase to eliminate dissolution effects. In the fully saturated aqueous phase, the Bentheimer sandstone/water system is (and remains) water-wet even at high pressures against CO 2 and/or flue gas. In these systems, the data of the stable contact angle demonstrate a strong dependence on the bubble size, which can be mainly explained by the gravity (buoyancy) effect on bubble shape. However, the surface nonideality and roughness have significant influence on the reliability of the contact-angle determination. The results of this study prove that in order to avoid the dependency of the contact angle on the bubble size in these systems, the effect of gravity (buoyancy) on bubble shape has to be considered by calculation of the Bond number; for systems characterized by Bond numbers less than 0.9, the influence of the bubble radius on the contact angle becomes insignificant. The experimental results show that, in contrast to quartz, the phase transition of CO 2 from subcritical to supercritical has no effect on the wettability of the Bentheimer sandstone/water system, which originates from differences in the surface charges of quartz and Bentheimer sandstone. In an unsaturated system, two dissolution regimes are observed, which may be explained by density-driven natural convection and molecular diffusion.

Enhancing residual trapping of supercritical CO2 via cyclic injections

“…As the pressurized CO 2 is pumped underground, it warms to in situ temperature of the storage reservoir; under the pressure and temperature conditions of most reservoirs targeted for CO 2 sequestration, the injected CO 2 will exist in a supercritical state (denoted scCO 2 in the present study) [Intergovernmental Panel on Climate Change, 2005;Benson and Cole, 2008]. Sandstones and other sedimentary formations provide favorable storage conditions [Bachu, 2003;Gunter et al, 2004]; and although wettability measurements of scCO 2 -brine-geologic media systems are thus far inconclusive [Wan et al, 2014], for sandstone formations, aqueous brine has been observed to be the dominant wetting phase while scCO 2 is the nonwetting phase Krevor et al, 2012;Pini and Benson, 2013;Herring et al, 2014;Kaveh et al, 2014]; these observations are supported by measurements of water-wet (or weakly water-wet) contact angles on surfaces representative of sandstones [Chaudhary et al, 2015]. The nomenclature used in the following reflects this assumption of water-wet porous media.…”

CO2wettability of seal and reservoir rocks and the implications for carbon geo-sequestration

“…[] and Kaveh et al . [], contact angle measurements depend on equilibration time between the fluids and the solid and on bubble size. They found that contact angle increases with progressing equilibration time but decreases with bubble radius if placed underneath the solid surface.…”

“…Kaveh et al . [] measured captive drop contact angles for the Bentheimer sandstone‐CO 2 ‐water system. The sandstone consisted of 96% quartz, ∼2% feldspars, and ∼2% kaolinite, and the kaolinite was homogeneously distributed throughout the rock matrix.…”

Investigation of Rock Wettability Alteration by Carbonated Water through Contact Angle Measurements

“…Furthermore, wettability alteration by CO 2 dissolution in brine has already been investigated for the systems of CO 2 -water-coal 9-11 , CO 2 -brine-Mica 12, 13 , CO 2 -brine-Quartz 12, 14 , CO 2reservoir brine-reservoir rock [15][16][17][18] and CO 2 -water-glass 19,20 ; however, very limited study focus on the wettability alteration of oil-brine-rock system with dissolution of CO 2 21 . Grape et al 22 performed imbibition tests involving CO 2 -enriched water (carbonated water).…”