Permeability reduction by gellan gum solutions

Abstract

This paper summarizes the results of laboratory experiments with gellan gum. Gellan gum solutions demonstrated plugging in distilled water and brine saturated sand packs. Progressive plugging in distilled water saturated sand packs is explained by the presence of gel particles in the gellan gum solutions, whereas plugging in brine saturated sand packs is explained by the instantaneous gelation of gellan gum upon contact with brine. Gellan gum gel strength and its injectivity depend on brine salinity in the rage of 0–60 g⋅L−1. Gellan gum plugging behavior in porous media depends on polymer concentration, permeability, and temperature. However, in these tests internal pressure taps were not used, making conclusions impossible as to whether gellan gum solutions provide in-depth plugging in matrix rocks. Fracture models with an impermeable matrix and fractured sandstone cores were used in this study to compare gellan gum and hydrolyzed polyacrylamide gels. Alternating injection of gellan gum and brine demonstrated an effective way to plug 1-mm-height fractures. The plugging efficiency of polyacrylamide gel depends on the initial viscosity of the solution, if it is injected prior to gelation, and post flush salinity. Whereas in the case of gellan gum, these factors are not critical because the solution gels instantaneously upon contact with brine, with higher brine salinity improving gel strength. Although, maximal gel and post flush injection pressures were several times higher in the case of gellan gum, stabilized post flush injection pressure was higher in the case of hydrolyzed polyacrylamide gel placed as a mature gel in a sandstone fractured core.