Evaluation of Alkaline Sodium Silicate Gel for Reservoir In-Depth Profile Modifications to Enhance Water Sweep Efficiency in Sandstone Reservoirs

Abstract

Alkaline sodium silicate (Na-silicate) is addressed to be applied for in-depth water conformance control in sandstone reservoirs containing high permeability layers.

The main factors affecting the gel time, strength and shrinkage in the alkaline silicate systems are the Na-silicate content, the pH, the presence of divalent ions and temperature. Divalent ions, e.g., Ca2+ and Mg2+, reduced the gel time and increased the gel strength and shrinkage. They also caused metal silicate precipitation at high concentrations. No precipitation formed with low-salinity water (25-times diluted seawater), which makes it a possible option for preflushing reservoir in field application.

Temperature accelerated the gel time but the gel strength was shown to be reduced as temperature increased from 20 to 50 °C. Further increase in the temperature to 80 °C showed a slight increase of the gel strength. This may be attributed to increase of silicate solubility at high temperature. High shear rates, even for a short interval before gelation (which resembles the wellbore case), accelerated gel time; hence must be considered in field applications. A simple graphical method was suggested to estimate the combined effects of different factors on the gel time and strength.

Dynamic adsorption of silicate in sand-packs was considerably lower than the estimated mono-layer adsorption. It was demonstrated that silicate adsorption is reversible, and most of the adsorbed mass is desorbed in the post-flush water. Na-silicate showed water-like injectivity in flooding experiments.