A Novel Polymer Gel System for In-Depth Water Conformance in High Temperature and High Salinity Reservoirs

Abstract

Abstract Delayed polymer gel systems have been the leading in-depth water conformance control agents in enhanced oil recovery applications. However, most polymer gel systems had limitations to tolerance high temperature and high salinity conditions. The objective of this work is to develop a new delayed polymer gel system that could form stable gels at 80-100 ℃ in brines with salinity up to 200,000 mg/L and a gelation time of more than 3 days. The gelation tests of a new Acrylamide-ATBS copolymer and a crosslinking agent were performed in anaerobic chambers around 90 ℃ in various synthetic brines with salinity of 50,000 to 200,000 mg/L. Gelation profiles and relationships between gelation time and polymer and crosslinking agent’s concentrations were obtained. Sydansk Gel Code was used to determine gel strength. Sandpack and coreflood experiments were performed to evaluate in-situ gel strength and long-term stability and to measure polymer and crosslinking agent’s adsorption/retention. The gelation profiles of gelation systems with polymer concentration ranging from 2500-4500 mg/L and crosslinker concentration from 100-1000 mg/L showed that the gelation time was 3-30 days around 90 ℃ with a low pre-gelation viscosity. The gelation time was varied by either the concentration of the polymer or that of the crosslinker and the brine salinity. The gel strength ranged from Code C to Code F. Sandpack and coreflood experiments of injected gelant showed formation of strong gels in-situ with low polymer/crosslinker retention. The permeability reduction of the cores plugged by the polymer gel was greater than 99% and the plugging was effective for more than 12 months. This work presents a new two-components polymer gel system with low pre-gelation viscosity, long and tunable gelation time, good gel strength and long-term stability to effectively shutoff high permeability channels/zones for in-depth conformance control in high temperature and high salinity reservoirs.