# Evaluation of Chromium-Crosslinked AMPS-HPAM Copolymer Gels: Effects of Key Parameters on Gelation Time and Strength

## TL;DR

This study evaluates chromium-crosslinked AMPS-HPAM gels for controlling CO2 movement in reservoirs, showing they are durable and adaptable to harsh conditions.

## Contribution

The paper provides new insights into the gelation behavior and stability of chromium-crosslinked AMPS-HPAM gels under CO2 exposure.

## Key findings

- Gelation times can be controlled between 5 to 10 hours with minimal dehydration under CO2 exposure.
- Gels remain structurally stable for over 10 months at 100 °C.
- Key parameters like polymer concentration and pH significantly influence gelation behavior.

## Abstract

Controlling CO2 channeling in heterogeneous reservoirs remains a major challenge for both enhanced oil recovery (EOR) and secure geological storage. AMPS-HPAM copolymers exhibit high-temperature resistance and brine tolerance compared with conventional HPAM gels, making them well suited for the harsh environments associated with CO2 injection. Chromium-based crosslinkers (CrAc and CrCl3) were investigated because sulfonic acid groups in AMPS can coordinate with trivalent chromium ions, enabling dual ionic crosslinking and the formation of a robust gel network. While organic crosslinked AMPS-HPAM gels have been widely studied, the behavior of chromium-crosslinked AMPS-containing systems, particularly their gelation kinetics under CO2 exposure, remains less explored. This experimental study evaluates the gelation behavior and stability of chromium-crosslinked AMPS-HPAM gels by examining the effects of the polymer concentration, molecular weight, polymer–crosslinker ratio, temperature, pH, salinity, and dissolved CO2. The results clarify the crosslinking behavior across a range of formulations and environmental conditions and establish criteria for designing robust gel systems. Gelation times can be controlled from 5 to 10 h, and the resulting gels maintained structural integrity under CO2 exposure with less than 3.6% dehydration. Long-term thermal testing has shown that the gel remains stable after 10 months at 100 °C, with evaluation still ongoing. These results demonstrate that chromium-crosslinked AMPS-HPAM gels provide both durability and tunability for diverse subsurface conditions.