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

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. Hydrogels have been successfully applied as remediation treatments to control water production from thief zones, natural fractures and matrix formation. In this study, a new polymer gel system (PGS), a hydrogel type, was examined for water control treatments. The experimental work included swelling testing, viscosity measurement, and coreflood experiments. The effect of water salinity, PGS concentration, pH values and temperature on hydrogel polymer system properties was examined. The PGS concentrations examined in this study were 0.5 and 1.5% while water salinity ranged from 20 to 200 g/L of NaCl. The examined pH values were 7 and 1. The coreflood experiments were conducted at 80 °C using sandstone core plugs. The results showed that viscosity of the polymer gel system increased as a function of concentration and temperature but decreased as a function of water salinity. The viscosity of PGS 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. Salinity was found to be negatively impacting the swelling properties of the examined PGS too. Coreflood experiments showed that the PGS 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 a lower injecting rate, the PGS was found to form an external filtercake at the inlet face of the core plug. The paper presents in detail lab findings of evaluation of a new hydrogel polymer system and recommend optimum conditions to control water production successfully.