Application of the dual-drop dual-crystal contact angle technique to characterize heavy oil reservoir wettability

Abstract

Reservoir wettability characterization is often important for planning and predicting depletion strategies, including primary and enhanced recovery schemes. This paper compares wettability evaluations in terms of water-advancing contact angles measured using the recentlydeveloped 'dual-drop-dual-crystal (DDDC)' technique with the traditional 'modified sessile drop' procedure. The DDDC technique was found to be a more reliable method for the Elk Point crudeoil/brine/rock systems. The DDDC experimental procedure is less time consuming because this technique achieves rapid adsorption equilibrium between two crude oil drops and two crystal surfaces. Moreover, it is reproducible as it is designed to overcome the difficulties commonly associated with the traditional contact angle methods. On the basis of the DDDC contact angle experiments, it was concluded that both the Lindbergh and Frog Lake Cummings heavy oil reservoirs of the Elk Point field exhibited intermediate wettability near the native reservoir conditions (characteristic of primary depletion). The water-advancing contact angles for the crude-oil/brine/quartz systems (near the reservoir conditions of 4400 kPa and 28°C) were determined to be 92 and 90° for Lindbergh and Frog Lake systems, respectively. These angles were reproducible within 1°. This reproducibility is the result of meticulous application of wateradvancing contact angle definition by means of a procedure that recognizes the effects of adhesion and buoyancy and allows shifting of the lower crystal so that the brine advances over an area that was previously exposed to crude oil. In addition, a careful monitoring of three-phase (oil/water/solid) contact line movements ensures conformance to the definition of water-advancing contact angle as demonstrated in this paper.