Influence of rock type and initial oil saturation on wettability during waterflooding of carbonate rocks.

This paper deals with the influence of wettability on carbonate rocks waterflooding. We present an experimental study performed on two carbonate rocks of almost the same mineralogy but presenting unimodal and bimodal pore size distribution. The steady state method was used to establish different levels of oil saturation in the cores before an ageing period in presence of crude oil to change the core wettabilty. We show that the responses to wettability alteration for the same oil/brine system depends strongly on the rock type. The change of wettability, from water wet to oil wet occurs when initial oil saturation exceed a given value that depends of the considered limestone. This behavior is attributed to the destabilization of water films that depends on the rock surface roughness.