UNDERSTANDING IMBIBITION DATA IN COMPLEX CARBONATE ROCK TYPES (original) (raw)

Carbonate rocks are complex in their structures and pore geometries and often exhibit a real problem in their classification and behavior. Many petrophysical and fluid flow properties remain unexplained and perhaps uncertain because of improper characterization of the reservoir rock. In this research, carbonate rock types were defined from thin-sections based on the structure of the rock together with its pore types. The rock type classifications were improved by incorporating pore-throat size distribution and poro-perm information, and high resolution plug CT images. This would lead to a robust rock typing scheme that should facilitate the understanding of heterogeneity effects on reservoir flow properties. Laboratory-measured imbibition relative permeability (Kr) data were determined on reservoir core samples in two " mixed-wet " carbonate fields from the Middle East region. The Kr curves were explained based on the identified rock types and gave consistent trends. The Kr curves were fitted with Corey exponents, and yielded high " no " and low " nw " for the higher permeability samples, which may be wrongly interpreted as more oil-wet rocks compared to the lower permeability samples. The variations in Kr curves with the different rock types were argued to be the result of different rock structures and pore geometries that control pore accessibility and surface area. The obtained Krw and Kro data from steady state experiments are not abundant in the literature and hence should serve as an important piece of information in mixed-wet carbonate reservoirs with varying rock types.