Disproportionate filtration behaviors of polymer/chromium gel used for fracture plugging

Abstract

Polymer/chromium gel is commonly used for fracture plugging in naturally or hydraulic fractured formation. At present study, the filtration behavior of polymer gelant in fracture was investigated. According to the results of gelant analysis, the filtration degree of Cr3+ is obviously higher than that of polymer molecules, which verifies the disproportionate filtration behaviors of gel components. Polymer has great impact on the filtration behavior of Cr3+. Because of the thickening, entrapping and cross-linking effects, the filtration degree of Cr3+ can be greatly decreased by polymer molecules. Moreover, the adsorption layer of polymer molecules on fracture wall, the accumulation layer near the adsorption layer, and the retention layer in the matrix can also significantly hinder the filtration of Cr3+ from fracture into matrix. Results of fractured core flowing experiments show that both the filtration depth of gelant and the filtration degree of Cr3+ from fracture into matrix are reduced with the increase of polymer concentration. In addition, high injection pressure differential contributes to high filtration degree of Cr3+, which further results in the intense disproportionate filtration of gel components. What’s more, with the fracture width increasing and matrix permeability decreasing, the filtration degree of Cr3+ is greatly declined. Research results can provide theoretical reference for improving the water plugging performance of polymer gel in hydraulic fractured formation.