Conformance gels based on nanosilicas are used as environmentally acceptable materials for plugging and sealing water- or gas-producing zones and controlling water production. Because of the lower pH(compared to sodium silicate solutions) of these solutions, they are environmentally acceptable in the North Sea area. The gelling agents required to activate the materials to produce gels are typically common salts, such as sodium chloride and potassium chloride.
The reduced environmental impact of nanosilica has led to its commercial success in the North Sea. At temperatures greater than 80°F, the gel time of nanosilica can be controlled to desirable values by adjusting concentrations of the gelation agents. The nanosilicas that are currently used in the oilfield, however, are not suitable for low-temperature applications (e.g., below 80°F) because of extremely long gel times.
This paper describes a new nanosilica system that demonstrates non-spherical-shaped nanosilica particle assemblies, such as rod-like and string-of-pearl geometries that display superior gelation activity in the presence of salts, exemplified by sodium chloride, compared with their spherical counterparts. These materials can gel in a reasonable time frame in the presence of an activator at temperatures as low as 50°F.
A trend of increasing reactivity in nanosilicas based on their geometries is presented in this paper. In particular, nanosilicas with a high aspect ratio render stable gels in a shorter period of time than their spherical counterparts. It is proposed that the aspect ratio could enable formation of a networked superstructure of silica at lower concentrations than required for a networked structure of nanosilica spheres of similar diameter.