An Investigation of In Situ Gelation of a Polyacrylamide/Chromium(III) System in Porous Media

Abstract

Crosslinked polymer systems are used in enhanced oil recovery treatments. To further understand the behavior of such systems in porous media, the flow of a chromium(H[)-polyacrylamide gel system has been studied in unconsolidated porous media. In this research, a suitable chromium(III)-polyacrylamide system was identified to allow the experimental investigation of gel polymer displacements under laboratory conditions. The flow and gelation behavior of the chemical system identified was observed and measured in unconsolidated sandpacks. The effect of flow rate on the flow resistance developed in the sandpacks was determined. In addition, a previously developed mathematical model of permeability reduction by chromium(III) polyacrylamide systems flowing in unconsolidated porous media was modified to simulate the displacement data obtained during the course of this research. The chromium(III)-polyacrylamide system was found to be sensitive to pH. The pH was carefully controlled in the displacement experiments. When the gelling system was injected into unconsolidated sandpacks, a region of high flow resistance developed which plugged the sandpack, causing injection to cease. The region of high flow resistance developed much earlier than gelation in quiescent beaker tests. The high flow resistance region was propagated deeper into the sandpack as the flow rate increased and was approximately a linear function of flow rate over the range of conditions examined. The experimental results provided the necessary data to modify and verify the mathematical model of in situ gelation. Good agreement was observed between experimental and computed permeability reduction verifying that filtration of gel aggregates causes permeability modification when chromium(III)-polyacrylamide systems are injected into unconsolidated sandpacks.