Wettability study of calcium carbonate using zeta-potential measurements

Abstract

Wettability study using the zeta potential technique is a novel approach proposed for carbonate reservoir rocks. Simpler than other existing industrial and laboratory methods, such as the Amott-Harvey, the USBM and the contact angle method, the zeta potential technique provides a complete wettability profile of limestone in presence of water for different oil samples. The study relies on the finding that carbonated reservoir rocks, consisting of CaCO3 mainly, are positively charged and their surface has the potential to adsorb significant quantities of anions. In this study, the proposed zeta potential technique was used to study the wettability of limestone for three different crude oil samples. In addition, the study is extended for oil derivatives such as asphaltenes and maltene. A case study was also carried out to understand the effect of asphaltenic solutions on wettability of limestone rocks as well as the effect of inhibitors on crude oil. The mechanism of inhibitor interaction with the rock surface, as well as the wettability alteration process due to asphaltene was explained comprehensively. Wettability profiles were achieved for the different oil samples, indicating the transition between water-wet to oil-wet. Models were fitted to experimental data, showing the wettability profile of limestone for crude oil and asphaltenic solutions of varying concentration. Maltenes, comprising mainly of resins, were found to be the initial oil component that competitively adsorbs onto the surface of limestone, displacing the water from the surface. Asphaltenes then displace these resin molecules by adsorbing onto the surface. Effective inhibitors aided in increasing the rock's resistance to this wettability alteration. A logistic model was fitted to the wettability profile of limestone for the crude oil and the R-squared value for the fit was calculated to be 0.99 with a standard deviation of 0.61 mV. On the other hand, a cycloid model was fitted to the wettability profile of limestone for asphaltenic solutions with varying concentration. The R-squared value for the fit varied within the range of 0.86-0.98 whereas the standard deviation varied within the range of 0.50-0.79 mV.

Date of Award	2013
Original language	American English
Supervisor	Ghada Bassioni (Supervisor)