Optimizing carbonate core restoration procedures - Effect of crude oil saturation and mild cleaning

Abstract

Wettability has a big impact on how much we can recover by water flooding a reservoir, and there is a commercial potential for improvement done through alteration of the wettability. Studies have been conducted and shown that Smart Water can enhance the recovery significantly by manipulating the composition in the injected water. Optimized core restoration procedures reproducing reservoir wettability are important when core experiments are performed in the laboratory.

A Stevns Klint outcrops chalk core with S_wi = 0.1 has initially gone through a restoration with a crude oil containing polar acidic components. Spontaneous and forced imbibition experiments together with chromatographic wettability test have been used to give a basis for discussion of initial rock wettability.

The effect of mild core cleaning and a second core restoration on wettability have then been evaluated. The experiment shows that mild cleaning did not influence the wettability significantly conserving the polar components that have been established on the surface of the carbonate. The results confirm that the amount crude oil the core is exposed to during core restoration is the dominant factor regarding the establishment of core wettability. The spontaneous imbibition gave a much lower and slower oil recovery after the core had been exposed to oil a second time.