Many conformance control treatments rely on the ability of gels to extrude through fractures during the placement process. This paper describes an experimental investigation of the mechanism for propagation of a Cr(III)-acetate-HPAM gel through fractures. When large volumes of this gel were extruded through a fracture, progressive plugging (i.e., continuously increasing pressure gradients) was not observed. Effluent from the fracture had the same appearance and a similar composition as those for the injected gel, even though a concentrated, immobile gel formed in the fracture. The concentrated gel formed when water leaked off from the gel along the length of the fracture. The driving force for gel dehydration (and water leakoff) was the pressure difference between the fracture and the adjacent porous rock. During gel extrusion through a fracture of a given width, the pressure gradients along the fracture and the dehydration factors were the same for fractures in 650-md sandstone as in 50-md sandstone and 1.5-md limestone. A simple model was developed that accounted for many of the experimental results.

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