Relative permeability modifiers (RPMs) are chemicals that can be injected into a reservoir to change its fluid/gas transport characteristics. For example, RPMs can reduce the relative permeability to water in a subterranean reservoir while having minimal impact on hydrocarbon production. Most commercially available RPMs are specifically designed for silica surfaces which are dominant in sandstone reservoirs. However, the concentration of silica in carbonate rocks is very low and many of these RPMs are unsuitable for carbonate reservoirs (which hold a significant portion of the remaining 60% hydrocarbon reserves). Furthermore, carbonate reservoirs tend to have more complex permeability and porosity characteristics and as such few research publications report the utilization of RPMs in the reservoirs of this type. The main mechanism of RPMs is either chemical adsorption onto, or functionalization of, a rock surface. However, as carbonates have distinctly different chemistry compared to silica, a new RPM formulation is required. The approach reported here overcomes this obstacle by using sodium silicate to functionalize the carbonate rock surface thereby converting it into a surface that in many ways exhibits the chemistry of silica. This has been confirmed by sodium silicate adsorption tests and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis. The other components consist of an amine-containing silylation reagent which reacts with the newly formed silicate surface, a polymer containing amine functional groups, and a linker molecule that reacts with the amines on the silane immobilizing the polymer. The chemistry is confirmed using five different chemical solutions to investigate their adsorption onto carbonate rocks using static tests. The results show that carbonate particles treated by the RPM have the highest adsorption weight, 7.33 mg/g and according to the measurements of X-ray photoelectron spectroscopy (XPS), the atomic percentage of Si 2p and N1s is 9.89% and 7.51% respectively, indicating the adsorption of RPM onto carbonate particles. To further verify the performance of RPM under reservoir conditions (1500 psi and 60 °C), three core flooding tests have been conducted. The results show that relative permeability to water decreased much more than oil. RRF to water in sample indinana-2 can reach up to 5.21, but RRF to oil is less than 2. The disproportionate ratio (RRF brine /RRF oil ) is 3.1, indicating the good performance of RPM under reservoir conditions. This work first introduced sodium silicate and APTES to make polyacrylamides as a new RPM material strongly stabilized onto carbonate rock surfaces, which provided further insights into the effectiveness of this approach applied in carbonate reservoirs.
Multiphase fluid flow characteristics of a reservoir rock, such as capillary pressure, displacement efficiency, relative permeability, and saturation distribution are substantially influenced by the wettability state of the rock. Being able to change the affinity of the rock toward different fluid phases present in the formation has implications in various petroleum applications (e.g., CO 2 geo-sequestration, EOR, gas production). In this study, silylation of sandstone core samples using nonfluorinated compounds is accomplished using supercritical CO 2 as a solvent and carrier. This approach is cost-effective and less environmentally sensitive compared to other approaches which use fluorinated silylation reagents. By using small molecules to only change the wettability characteristics of core samples without altering other parameters (e.g., rock pore structure) noticeably, the effects of wettability alteration alone on multiphase flow (i.e., relative permeability) can be identified. Spontaneous imbibition tests were conducted on Gray Berea sandstone before and after silylation treatment, which showed a diminished rate of water uptake in the post-treatment sample. The wettability alteration caused by this functionalization and its impact on multiphase flow characteristics were analyzed using core flooding tests. The experimental results show that supercritical CO 2 -based (scCO 2 -based) silylation changes the wettability of the formation from strongly water-wet to intermediate gas-wet. Core flooding tests showed that the effective permeability for the water phase was significantly increased, resulting in higher water removal from the rock matrix. Furthermore, the relative permeability for the gas phase (in this study, CO 2 ) at residual water saturation is higher after treatment. Such an outcome confirms that the change in wettability could be beneficial in geological CO 2 storage as well as gas production.
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.
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