Laboratory Studies of Capillary Interaction in Fracture/Matrix Systems

Summary Current study of fractured petroleum reservoirs often is based on the assumption of capillary discontinuity between matrix blocks. Both theoretical analysis and examination of the field performance of some fractured reservoirs, however, indicate a degree of capillary interaction between matrix blocks. Experiments performed to gain an understanding of the capillary continuity across a stack of matrix blocks are described. Three matrix blocks with a total length of 3 ft [90 cm] were stacked and placed in a transparent core holder. Before the experiments with stacked blocks were conducted, rock properties, capillary pressure, relative permeabilities, and the aperture/overburden relationship were measured. Drainage capillary pressure data showed a threshold height of the same size as each of the individual matrix blocks. Experimental results showed a strong capillary interaction (capillary continuity) between the neighboring blocks. Recovery from the top two matrix blocks far exceeds that from the same blocks when the assumption of capillary discontinuity is used. We believe that incorporation of the capillary-continuity concept in dual-porosity models will result in more realistic simulation of fractured reservoirs.