Gelation studies of an organically cross-linked polyacrylamide water shut-off gel system at different temperatures and pH

The use of gel as the water shut-off agent has been widely reported in enhanced oil recovery (EOR) of mature oil fields. The organically cross-linked polymer systems are preferred due to their greater thermal stability and suitability over wide pH range. Polymer gels are used successfully in many reservoirs all over the world, but it is difficult to find a suitable economical polymer for the harsh reservoir conditions of high temperatures and salinity. Some polymer gels are carcinogenic in nature whereas some are non-ecofriendly. In recent times cross-linkers such as chromium (III) acetate and phenol-formaldehyde are commonly used, even though they are toxic. In this paper, polymer gel comprised of polyacrylamide (PAM) as a water soluble polymer and hydroquinone (HQ) and hexamethylene tetramine (HMTA) as organic cross-linking agents of low toxicity was prepared as water shut-off system to control water production. The effect of various parameters such as temperature, pH, salinity etc. was evaluated on the gelation time and gel strength using bottle testing and viscosity measurement methods. The gel formed by cross-linking HQ and HMTA with PAM is found to have high mechanical strength, form gels at high temperature of about 120 degrees C and is cost-effective. The gelation temperature was varied from 85 degrees C to almost 120 degrees C to study the variations in the performance of the polymer system. This study suggests that the present low toxic gel system can be used in high temperature reservoirs. (C) 2011 Elsevier B.V. All rights reserved.