Spontaneous imbibition in two different chalk facies

An evaluation is made of the imbibition potential of two different chalk facies from outcrops in England and Denmark. Both chalk facies have low permeability, moderate to high porosity, and comparable low insoluble residues (< 5%), but different texture, depositional origin and diagenetic history. Spontaneous imbibition experiments were carried out on plugs with low initial water saturation and North Sea dead oil. Distinctly different production rates and production plateaus were observed for the two chalk facies. Careful investigations of the rock framework and pore system of the sample material form the basis for a theoretical description of wettability alteration and possible imbibition processes in the two chalks. The theoretical descriptions are used to rationalize the results from the spontaneous imbibition experiments. The results suggest that by knowing lithology, depositional history and degree of diagenetic alteration a relative potential of spontaneous imbibition in different chalk facies may be elucidated.