Effect of Shear on Gelation of Polyacrylamide-Chromium Acetate Gelant in a Circular Tube

Abstract

This research studies the gelation and flow properties of a partially hydrolyzed polyacrylamide (HPAM)-chromium acetate gel system under shear conditions. Gelation was observed in steady shear on a rheometer and during injection through a 1,031-ft long stainless steel tubing. Fluid experienced continuously non-uniform shear in the tubing (zero shear at the center and maximum shear at the tube wall) and the shear environment may not be reproduced by rheometers. Both in-line-mixed and preformed gels were injected through the tubing, and gel samples were collected to determine syneresis. Interesting results were observed due to the non-uniform shear rate distribution in the tube. During injection of in-line-mixed gelant solution, flow resistance developed with length down the tube to a steady resistance value. Shear retarded the gelation process as compared to a quiescent bulk gel. Spaghetti-like gel emerged from the tube, and the low apparent viscosity of the gel in the tube indicated the existence of lubricant solvent between the gel and the tube wall. During injection of preformed gels, flow resistance at upstream of the tube was higher than that of in-line-mixed gelant. However, it decreased down the tube to steady values that were lower than the steady values measured for in-line-mixed gelant. The effluent gel more easily broke into pieces than the effluent during the injection of in-line-mixed gelant solution. Effluent samples from both types of flow experiments underwent significant syneresis due to the shear experience in the tube; while bulk-mixed gel samples were stable. Samples placed under constant, steady shear in a rheometer for 10 hours did not form strong gels until the shear was stopped. This study shows that shear experienced by a gelant during displacement in the reservoir significantly affects the properties of the gel. Results of the study are applicable to gel placement in fractured reservoirs.