Is There a Correlation Between Wettability From Corefloods and Contact Angles?

Abstract

Abstract Laboratory coretloods have constituted a major step in understanding many aspects of fluids flow behaviour in reservoirs. The reservoir rock samples, having been retrieved from the oil-bearing formations, have been most valuable since they represent the actual solid phase of the reservoir rock-fluids system in laboratory studies. Therefore, it is only natural that we try to maximize the information that can be extracted from these cores and corefloods Oil-water relative permeabilities are perhaps the most widely derived parameters from such corefloods and they are the only recourse to account for all the rock-fluids interactions in the mathematical models developed to describe the reservoir flow phenomena Thus, coring, core preservation, core analysis, core flooding, and coreflood data analysis have formed the basis of our knowledge on reservoir fluid mechanics. One of the factors that has a strong influence on reservoir fluid mechanics is rock wettability. Therefore, attempts to derive wettability from corefloods are abundant in the literature that spans several decades. On the other hand, contact angles observed in crude oil-water-solid systems have been traditionally regarded as a true or universal measure of wettability. Hence the obvious question - is there a correlation between wettability derived from corefloods and contact angles? A definitive answer does not seem to emerge from the literature for two main reasons: (1) Craig's broad rules-of-thumb, while enabling approximate comparisons especially between extreme cases of wettability, do not allow direct deduction of rock-fluids interactions to the extent that is required to characterize wettability, and (2) the conventional contact angle measurements have had their own share of problems in terms of reproducibility. The dual-drop-dual-crystal (DDDC) contact angle technique, recently reported in the literature1, appears to resolve this long-standing repr- oducibility problem with contact angle measurements. This presentation aims to compare wettability derived from reproducible DDDC tests in widely differing rock-fluids systems with their corresponding oil-water relative permeabilities derived from waterflood experiments using reservoir and Berea cores In all, a total of six different case studies are compared in which four rock-fluids systems appear to yield similar wettabilities from corefloods and contact angles while the others differ markedly Explanations are sought for these agreements and differences in an effort to shed more light on this important aspect of correlating core analysis with distribution and flow mechanics of reservoir fluids.