Gas condensate recovery in carbonate rocks through wettability alteration: Characterization and optimization by response surface methodology (RSM)

Abstract

Liquid blockage around the wellbore region can significantly decrease the gas and condensate extraction volume from a condensate reservoir. In these kinds of reservoirs, the rock surfaces are commonly liquid-wet. Treatment to alter rock preference from liquid to gas is a versatile, permanent, and effective technique for recovery enhancement. A novel chemical solution containing fluorosurfactant and nanoparticles is suggested to modify the wettability of carbonate rock. The hydrophobicity of nano silica is achieved using (3-chloropropyl) trimethoxy silane. The chemical solution can provide a gas-wetting tendency in rock samples by inducing a combination of high surface roughness and low surface energy. Modification of wettability by this chemical was confirmed through static contact angle experiments. FTIR and FESEM were used to study the adsorption of the chemical agent on the rock surface, while EDX analysis and EDX map were employed to characterize the elemental composition of the rock surface and determine the distribution of elements on the coated surface before and after treatment. To determine the effective parameters of the chemical treatment process including fluorosurfactant and nanoparticle concentration, treatment time, and temperature, statistical analysis was conducted through analysis of variance (ANOVA) on the modified cubic model for two response variables, water contact angle (R1) and condensate contact angle (R2). The R² values of 0.9973 for the water contact angle and 0.9893 for the condensate contact angle represent a close agreement between measured and estimated values. Process parameter optimization was conducted using a desirability function to maximize the response variables associated with the liquid-repellent state. The optimal parameters for the process were identified as fluorosurfactant concentration of 4.96 wt%, SiO₂ nanoparticle concentration of 0.76 wt%, treating time of 2.49 days, and treating temperature of 23.24 °C. To validate the optimization method, a confirmatory experiment was conducted. This experiment achieved the highest water and condensate contact angles of 148.10° and 112.82° under the optimized conditions. The EDX analysis and EDX mapping imply that a homogeneous and evenly distributed fluorine-based layer formed on the rock surface through the adsorption of the chemical agent onto the surface of the rock. This layer induces liquid repellency, making the rock surfaces resistant to both water and oil. Also, the FESEM images indicate a substantial level of roughness on the treated rock surface, attributed to the presence of nanoparticles. FTIR analysis confirmed the adsorption of chemical agents onto the surface of the carbonate rock and presence of carbon and fluorine functional groups within the proposed chemical solution agents.