Gel Placement in Fractured Systems

Abstract

SummaryThis paper examines several factors that can have an important effect on gel placement in fractured systems, including gelant viscosity, degree of gelation, and gravity. For an effective gel treatment, the conductivity of the fracture must be reduced and a viable flow path must remain open between the wellbore and mobile oil in the reservoir. During placement, the gelant that "leaks off" from the fracture into the rock plays an important role in determining how well a gel treatment will reduce channeling. For a given volume of gelant injected, the distance of gelant leakoff is greater for a viscous gelant than for a low-viscosity gelant (other factors being equal).In one method to minimize gelant leakoff, sufficient gelation is designed to occur before the gelant leaves the wellbore. We investigated this approach in numerous experiments with both fractured and unfractured cores. We studied Cr(III)/acetate/hydrolyzed polyacrylamide (HPAM), resorcinol/formaldehyde, Cr(III)/xanthan, aluminum/citrate/HPAM, and other gelants and gels with various delay times between gelant preparation and injection. Our results suggest both hope and caution concerning the injection of gels (rather than gelants) into fractured systems. Tracer studies indicate that some gels can effectively heal fractures under the right circumstances. However, high resistance factors exhibited during placement could limit the ability to propagate certain gels deep into a fractured system unless the fractures are very conductive.