Wettability alteration in carbonates : the effect of water-soluble acids in crude oil and application of enzyme for wettability alteration

Abstract

The objective of the project is defined in two phases. The first phase is to study the effect of oil composition and carboxylic acids in the crude oil on the wetting condition and wettability alteration process using “Smart Water”. It has been reported that the major types of acidic compounds in crude oil were identified as carboxylic acids, phenols, carbazoles, and amides. The phenols and carboxylic acids comprise the major portion of the acidic species. The water soluble components of the carboxylic material are a small fraction of the total amount of carboxylic acids in the crude oil. They play an important role in establishing the initial wetting condition by contributing to destabilize the water film between the rock and oil. In this work, we have extracted water-soluble acids from a crude oil with high acid number (AN) to study the effect of these acidic materials on the wetting condition. Two crude oils have been prepared with almost the same acid number: the original oil, RES40 and synthetic crude oil containing only water-soluble acids termed EWS-oil. Two parallel cores were saturated and aged with each crude oil. The cores were subjected to spontaneous imbibition to study the oil displacement efficiency by “Smart Water”. The potentiality of seawater as a wettability modifier has been investigated previously. The mechanism of wettability alteration has been proposed based on the interactions between the rock surface and the potential determining ions Ca2+, Mg2+ and SO4 2- present in seawater. It was concluded that, not only the strength of the bonding of carboxylic material onto the calcite surface dictated by the carboxylic group, AN, is an important wetting parameter; but also the organic structure of the carboxylic material may have an impact on the wetting condition as well. The second phase of the project is to study the application of Enzymes to improve the wetting condition towards water-wetness. An enzyme-based method has already been reported, which generates organic acids for a variety of acidizing applications such as a matrix acidizing, the stimulation of natural fracture networks, damage removal over long horizontal intervals. The generation of acid in-situ following placement of the fluid ensures the even delivery of acid over the whole of the treated zone. Two cores were saturated and aged with the crude oil, RES40. After forced displacement with seawater depleted in sulfate and establishing residual oil saturation, the enzyme solution was injected into the cores and shut-in for 48 or 96 hours in an attempt to improve the wetting condition towards water-wetness. Later, the chromatographic wettability test was performed to monitor the change in the wetting condition. No improvement in the wetting condition and displacement efficiency was observed after enzyme injection.