Hydrogels for Water Shut-Off Treatments: Evaluation of a New Polymer Gel System

Abstract

Abstract Hydrogel polymers have served the oil and gas industry in different applications including water shot-off. Hydrogel polymers can create impermeable gels to optimize water injection profile, improve sweep efficiency, and seal undesirable permeable zones. They have been successfully applied as remediation treatments to control water production from thief zones, natural fractures, and matrix formation. In this study, a new hydrogel polymer system (HGPS) was examined for water control treatments in sandstone formations. The experimental work included swelling testing, viscosity measurements, and coreflood experiments. The effects of water salinity, HGPS concentrations, pH values and temperature on examined HGPS properties were investigated. The HGPS concentrations examined in this study ranged between 0.3 to 2%, while water salinity ranged from 20,000 to 250,000 mg/L of NaCl. The examined pH values were between 7 and 1 and the temperatures ranged from ambient to 90°C. The coreflood experiments were conducted at 80°C using sandstone core plugs. The results showed that the viscosity of the HGPS increased with concentration and temperature but decreased with water salinity. The viscosity of the HGPS at 1.5 wt% and at a temperature of 60°C decreased from 575 to 16 cP when the pH value was decreased from 7 to 1. The results also demonstrated that the salinity had a negative impact on swelling properties and, eventually, the HGPS viscosity. Coreflood experiments showed that the HGPS should be squeezed into the core plug at higher injection rates (below frac pressure) in order to achieve high water control. The residual resistant factor to water obtained at an injection rate of 5 cm3/min was 158 while it was found to be < 5 at an injection rate of 1 cm3/min. At lower injecting rate, the HGPS was found to form an external filtercake at the inlet face of the core plug. The paper presents in detail the major lab findings of the evaluation of a newly developed hydrogel polymer system and recommends the optimum conditions to control water production successfully.