Several laboratory experiments demonstrated that different water compositions cause rocks to change fromoil-to water-wet state.Although it is a consensus that wettability alteration is the main recovery mechanism,modeling the underlying mechanism is still a major challenge.Our main goal is to improve and validatea physically based model to predict contact angles from zeta-potential measurements.We propose a newmass-action formulation for surface complexation model(SCM)that includes the energy interaction effectbetween two close surfaces(PS).Currently,most SCMs consider rock and oil as isolated surfaces(IS).Thus,we hypothesize that,as rock and oil surface approach each other,PS model produce a better descriptionof electrostatic distribution.Additionally,we develop a method of determining SCM equilibrium constantsto fit several zeta-potential measurements for different ion concentrations(Na+,Ca2+,Mg2+,SO42-andH+).Finally,we estimate contact angles using disjoining pressure calculations and compare them withones reported in the literature.From a SCM set of reactions available in the literature,we validate thedeveloped IS model against PHREEQC(a reference simulator for geochemical reactions).For the PS case,the system of equations'solution is very close to IS approach when the interaction between surfaces arenegligible(wide spacing between surfaces).Regarding zeta-potential prediction for calcite-brine system,we argue that Na+ might not be an indifferent ion as suggested previously.Our simulation results indicatethat,besides the renowned potential-determining ions,sodium adsorption on calcite can play an importantrole in electrostatic interactions,switching surface charge polarity.Thus,we only achieve a successfulfit of zeta-potential measurements when Na+ is considered in the SCM reactions.Finally,contact angleestimation using the PS model and disjoining pressure theory provide good predictions of seven differentcases reported in the literature.We validate our method on a total of 66 and 163 contact angle and zeta-potential measurements,respectively.The present work is a novel approach to represent how electrostaticinteractions among rock,brine and oil modify the rock surface charge and the rock wetting state.
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