On the adsorption behavior of a fluorochemical onto carbonate rock with the application of wettability alteration to a gas wetting condition

Abstract

In this study, some new aspects of adsorption of a fluorochemical onto carbonate rocks as a wettability alteration agent to a gas wetting condition with the potential application for reduction of condensate blockage in gas condensate reservoirs are presented. To achieve this, kinetics, equilibrium, and thermodynamic of the adsorption process besides contact angle, imbibition, and characterization tests are investigated. Results of adsorption experiments revealed that kinetics behavior of the utilized fluorochemical–calcite system obeyed the pseudo-second order kinetics model. There was no change in adsorption after about 20 h. Also, the intraparticle diffusion mechanism was not the only rate controlling mechanism of the process. For equilibrium condition, Freundlich isotherm, which supports multilayer adsorption of nanofluid onto calcite surface, matched well with the obtained data. Obtained enthalpy and of 15.8 kJ/mol and entropy of 127.9 kJ/mol from thermodynamic analysis showed the endothermic nature of the adsorption process and the tendency of the fluorochemical to be adsorbed onto calcite rock surface, respectively. Analysis of static contact angle measurement of water, crude oil, and n-decane on the treated calcite rock samples at different concentrationss and aging times resulted in two new mathematical expressions for concentration-dependent, which is based on Freundlich isotherm, and aging time-dependent, which is based on pseudo-second order adsorption kinetics, of wettability alterations. The parameters of proposed models matched well with the obtained experimental data and were evaluated for different fluid-rock systems. Results showed that the major part of wettability alteration occurs at <5 h. After the treatment, water, crude oil, and n-decane contact angles were increased from 65o, 0o, and 0o to 138o, 93o and 73o. Comparing spontaneous imbibition results before and after treatment of carbonate plugs confirmed reliable gas-wetting condition, and showed 77% PV and 81% PV reduction in imbibed water and n-decane, respectively. When coupled with an imbibition model, reduction of liquid permeability by a factor of 79% and 72%, respectively, was observed. Characterization of treated and untreated surfaces were performed through SEM, EDX, FTIR, XRD, and AFM tests. EDX revealed the presence of 9.5 wt% of fluorine on the treated surface. SEM and AFM disclosed that mean roughness of polished surface increased from 29 nm to 417 nm due to adsorption of spherical nanoparticles. Results of this study may provide a deeper understanding of adsorption of fluorochemical onto carbonate rocks as a potential wettability alteration agent to gas wetting condition in gas condensate reservoirs.