Changing Sandstone Rock Wettability with Supercritical CO₂-Based Silylation

Abstract

Wettability of subsurface reservoir rocks is a key parameter that influences multiphase flow characteristics of the fluid–rock system, including relative permeability, capillary pressure, saturation distribution, and displacement efficiency. To investigate such effects, various techniques have been implemented to change wettability, including nanoparticle injection, chemical treatment, surfactant injection, brine salinity adjustment, etc. However, most studies have focused on the use of model surfaces (e.g., mineral surfaces) and not actual rock samples, which are far more representative of real-world application. The ability to modify the wettability of the pore space in the reservoir has implications in a range of areas, such as reducing/preventing water/condensate banking around hydrocarbon production wells, CO2 geo-sequestration, enhanced hydrocarbon recovery, and separation of CO2 using porous media. In light of the above findings, in this research, we primarily explored supercritical fluid-based silane surface modification of quarried sandstones (i.e., Gray Berea, Upper Gray Berea, Bentheimer, and Bandera Brown). Using high-throughput treatment methods, these samples were treated with five different silanes and then characterized using X-ray photoelectron spectroscopy and contact angle measurements. Conventional techniques for depositing silanes onto a surface from organic solvent (i.e., toluene) were also conducted for comparison. In all of the cases studied, our experimental results show that, when supercritical CO2 (scCO2) is used as a carrier for the silanes, improved surface coverage and wettability alteration were achieved in comparison to when the conventional solvent (e.g., toluene) is used. As a result, the wettability of sandstone surfaces as measured under high-pressure conditions was altered significantly from strongly water-wet (θ ≈ 11 ± 5°) to strongly non-water-wet (θ ≈ 145 ± 6°). Furthermore, we showed that scCO2 at even relatively modest reservoir conditions (10 MPa at 60 °C) could be used rather than toluene for application in real-world scenarios; this reduces environmental and safety concerns significantly.

Rock/Fluid/Polymer Interaction Mechanisms: Implications for Water Shut-off Treatment

“…The adsorption of polymers in porous media is considered necessary for DPR as it immobilizes the polymer within the rock matrix thus allowing subsequent DPR mechanisms to manifest. ,,− Furthermore, it is well-established that the fluid (water and oil/gas) and rock interactions (attraction/repulsion) govern rock wettability, and this controls fluid distributions, capillary pressure, relative permeabilities, fluid transportation, and oil/gas recovery. − Consequently, the adsorption of a polymer in porous media is also a strong function of rock wettability. More specifically, during injection, a DPR fluid that wets the porous medium will be segregated mainly in the preferred pathways for wetting fluid, thus promoting its adsorption onto the rock surface.…”

Wettability Alteration in Gas Condensate Reservoirs: A Critical Review of the Opportunities and Challenges

“…This includes various characteristics such as relative permeability, capillary pressure, saturation distribution, and displacement efficiency. 40 Wettability alteration appears to be the only permanent technique available for recovery enhancement of gas condensate reservoirs. Liquid-wetting state of the rock surface around the wellbore leads to decreased mobility which is an important factor in liquid accumulation.…”

“…The wettability of reservoir rocks in subsurface formations is a crucial factor that impacts the behavior of multiphase flow within the fluid-rock system. This includes various characteristics such as relative permeability, capillary pressure, saturation distribution, and displacement efficiency . Wettability alteration appears to be the only permanent technique available for recovery enhancement of gas condensate reservoirs.…”

Wettability Alteration Using Silane to Improve Water-Alternating-Gas Injectivity

“…A more comprehensive study was carried out with different silanes and different sandstone samples using either supercritical CO 2 or toluene as the silane solvent carriers. All combinations of surfaces, silanes, and carrier fluids resulted in a water contact angle of more than 140°, indicating that the surfaces were rendered hydrophobic, with a slight improvement when using scCO 2 . Both of these studies investigated the use of silanes to alter wettability with a particular focus on the use of scCO 2 instead of conventional toluene to mitigate any environmental or safety concerns.…”