High Temperature Plug Formation with Silicates

Abstract

A high temperature grouting/plugging system is currently being developed for use in the prevention of lost circulation, water shutoff and steam flooding which focuses on using silicate hydrates as the plugging material. Silicates have been used to form stable grouts and cements for over 50 years because of their ability to gel and polymerize. This reaction has also been used successfully for water shutoff and to solve lost circulation problems in oil and gas drilling which require a plug to be formed at various weak spots in a well formation. The reaction happens in seconds to minutes (generally controlled by the mixing rate). In addition to their gelling action, silicates will also react with soluble metal salts to form insoluble hydrate plugs. An example of this is the reaction of soluble calcium chloride with sodium silicate to form insoluble calcium silicate hydrate (C-S-H) plugs.

This work describes a novel way to exploit silicates' unique gelling properties in an environmentally friendly and cost-effective manner to form plugs for use in water shutoff strategy, steam flooding, and high temperature grouting/plugging for lost circulation. We describe a means to introduce sodium silicate and an activator delivered downhole through a single tubular by encapsulating the activator in a material that is temperature sensitive, thus delaying the timing of the reaction until exposed to hot downhole conditions. The formation of C-S-H plugs has been studied over the range of 80oC (175oF) to 300oC (575oF) as well as the chemical stability of C-S-H for 10-12 weeks.

Soluble silicates contain three components: silica, alkali and water. Although silicates have been described as the metal salts of silicic acid, they actually exist as polymeric forms in solution. The fundamental building block of silicate solutions is the tetrahedral silicon atom at the centre of an oxygen-cornered, four-sided pyramid. In sodium silicate, each oxygen atom may be associated with a hydrogen or sodium atom or it may be linked to other silica tetrahedra, thus forming chains, cyclic or polymeric structures. Once formed, C-S-H plugs are stable and should be environmentally benign at high temperatures.