Pore Geometry Effect on Si, Trapping and Sor in Tight Carbonate Reservoirs

Abstract

Spontaneous imbibition is one of the key production mechanisms in fractured oil reservoirs. It is also an important process in tight gas formations, which has signi- ficant effects on the gas production after hydraulic fracturing. The objective of this research is to investigate the effects of pore throat sizes and connectivity on spontaneous imbibition behavior in tight carbonate rocks. Many plug samples were selected from various wells in the Middle East. The samples were characterized using X-ray CT imaging, thin-section photomicrographs, Helium porosity and gas permeability. High pressure mercury injection experiments (MICP) were performed in the primary drainage mode to obtain the pore throat size distributions, followed by mercury withdrawal tests to investigate the spontaneous imbibition curve and fluid trapping. The degree of pore connectivity was studied in the samples from thin-section photomicrographs and from primary drainage capillary pressure curves and were found in good relation with the mercury withdrawal behavior and residual fluid saturations. Higher permeability samples were characterized by lower entry pressures that showed higher tendency towards lower fluid (mercury) trapping. These results show important link between the rock nature and spontaneous imbibition and fluid trapping that can be deduced from mercury withdraw testing. Accurate prediction of spontaneous imbibition is crucial in many hydrocarbon reservoirs and such analyses help understand production mechanisms in different carbonate rock types.