Factors Affecting Alkaline Sodium Silicate Gelation for In-Depth Reservoir Profile Modification

Aly Hamouda,Hossien Amiri

doi:10.3390/en7020568

Abstract

Alkaline sodium silicate (Na-silicate) is environment-friendly and possesses water-like viscosity during the injection stage for in-depth reservoir treatment to enhance sweep efficiency. Gel setting time (tg) and gel strength are interrelated. Factors that accelerate tg are Na-silicate content (wt%), low pH, presence of divalent ions and temperature. Pressure drop across the gel accelerates syneresis; however, the gel appeared to remain intact. Presence of Ca2+ and Mg2+ ions is shown to increase gel strength. With a Na-silicate content of 4.5 wt%, for example, at a pH of 10.3 and a temperature of 20 °C, gel strength almost tripled and was reached about eight times faster at the combined tested concentration of 0.009 M, based on the average effect from the coexistence of both ions. Low-salinity water (LSW) has an ion composition of 25-fold diluted seawater, did not show precipitation, and could accordingly be a candidate for a pre-flush before the injection of a Na-silicate solution in the event of a field application. This is important since LSW for enhancing oil recovery is a popular method in oil industry. A suggested predictive tool (simple graphical method) to estimate the effect of different factors on gelation time and gel strength is presented.

Highlights

Water conformance control represents one of the major challenges in water-flooded reservoirs.Heterogeneities such as high permeable zones cause early water breakthrough and thereby low sweep efficiency
A Na-silicate content ranging between 3 wt% and 6 wt% is used as practical for the purpose of this work and for field application
Gelation time and gel strength are the major parameters affecting the application of gel for in-depth reservoir treatment to increase flow resistance in high permeable zones, and thereby enhance sweep efficiency by diverting the flooding fluids to low permeable zones

Summary

Introduction

Water conformance control represents one of the major challenges in water-flooded reservoirs. Heterogeneities such as high permeable (thief) zones cause early water breakthrough and thereby low sweep efficiency. Sodium silicate (Na-silicate) is studied here for use as the in-depth reservoir treatment, since it is environmentally benign and has initial water-like viscosity—and good injectivity—that favors deep placement. The gelation of Na-silicate could be controlled by numerous inorganic and organic compounds [4]. This makes Na-silicate suitable for reservoir permeability modification, which was first proposed by Mills about a century ago [5]. It is widely acknowledged that Na-silicate’s viscosity, gelation time and gel strength depend on various factors such as pH, temperature, salinity and mechanical shear rate [4]

Methods

Results

Conclusion