A new technique for reservoir wettability characterization

Adhesion of crude oil to the reservoir rock surface influences oil recovery in primary, secondary and tertiary operations. The various wettability measurement methods reported in the literature either do not account for the effects of adhesion on measured contact angles or they only indicate the presence or absence of adhesion without measuring contact angles. This paper reveals, for the first time, a new technique that includes the effects of adhesion on measured contact angles under reservoir conditions of pressure and temperature. In the new technique, the buoyancy forces are used to drain the water film between the crude oil drop and mineral crystal surface to obtain adhesion equilibrium before measuring advancing and receding contact angles with respect to aging time. This is accomplished by initiating the experiment with two separate crude oil drops on two parallel crystal surfaces and by mingling the two drops after a certain pre-determined aging time. This method has been given the name of Dual-drop-dual-crystal (DDDC) technique. Photographs and results of measured advancing and receding contact angles are presented to demonstrate the three-phase-contact-line (TPCL) behaviour in water-wet, intermediate-wet and oil-wet systems. Possible explanations are offered for the discrepancies in and poor reproducibility of the conventional contact angle measurement techniques. Of all the procedures published so far, the DDDC technique presented in this paper is the solitary one that includes the effect of adhesion in a quantitative and reproducible manner in characterizing reservoir wettability through contact angles.