Often, gas travels through microfractures and channels and requires the use of a solids-free chemical to adequately fill and block gas pathways. Recent years have shown sodium silicate as an effective and environmentally friendly treatment option. With lower oil prices and increasing regulatory requirements there is a greater need to improve treatment performance and reduce costs in the treatment of surface casing vent flows and gas migration. Recognizing these needs, the chemistry of conventional sodium silicate was modified to allow for a broader range of application and provide improved physical properties upon setting.
Conventional manufacturing methods produce aqueous sodium silicate with a defined range of molecular size, shape and charge. An alternative production method was developed that reduces the alkalinity and increases the silica ratio and is described as a high-ratio sodium silicate. The form and distribution of silica in solution is quite different than commercially available sodium silicate. The silicate molecules in solution are significantly larger and with a lower charge density. The change in silica structure positively impacts the setting of sodium silicate by polymerization and precipitation. Several of the commonly used setting agents used with sodium silicate and/or colloidal silica were investigated with the high-ratio sodium silicate. Compared to conventional silicates, the high-ratio silicate could achieve longer set times and was less prone to variations in setting agent concentration. Upon setting, the high-ratio sodium silicate showed excellent dimensional stability with significantly less setting agent requirement vs. conventional silicates.
Initial field trials took place in Western Canada using two distinct placement techniques. The first approach was to squeeze the high-ratio silicate into microchannels as a standalone product. The second approach was as a compliment to a cement squeeze. Field results ranged from complete zonal isolation to reduced levels of gas migration. Where gas migration was not completely eliminated, data suggested that not all pathways were squeezed and/or there were secondary sources of gas. On-going field trials will allow for improvements and comparisons of placement techniques.