Gelation Time Optimization of an Organically Crosslinked Polyacrylamide Gel System for In-Depth Fluid Diversion Applications

Abstract

AbstractConformance improvement is crucial for heterogeneous reservoirs to ensure injected water and any EOR chemicals optimally contact the remaining oil with minimal throughput. Gel-based conformance control has been successfully applied on both sandstone and carbonate reservoirs. In this work, a laboratory study was conducted to investigate the applicability of an organically crosslinked polymer gel for in-depth fluid diversion practice at high-salinity and high-temperature conditions. The evaluated gel system was a polyacrylamide polymer crosslinked by organic crosslinkers, hexamethylenetetramine (HMTA) and resorcinol. The effects on gelation performance of polymer and crosslinker concentrations, brine salinity, and pH were investigated. Results showed that the gelation time of the studied gel system reached around three to four days at 95°C, with sufficient gel strength and long term stability. Gelation time became longer with decreasing either polymer or crosslinker concentrations, but there were lower concentration limits to form gel. The gel had a wide range of tolerance to brine salinity, but was sensitive to solution pH value. Decreasing pH resulted in faster gelation rate, and gel tended to be stronger. The gelation time slightly increased with increasing brine salinity in low pH range (< 6.0), or with decreasing brine salinity in neutral pH (6 to 8) environment. Varied laboratory techniques, dynamic rheology and low-field nuclear magnetic resonance (NMR) measurements, were also used to evaluate the gelation time of bulk gel. Rheological measurement and NMR technique, with minimum or no disruption to the gel structure, can determine the gelation time of a bulk gel sample that might be difficult to detect by bottle test. The determined gelation time by these two methods tended to be shorter than bottle test result.