During drilling or cementing, lost circulation may be encountered due to the presence of highly permeable formations, e.g. high natural permeability in a sandstone, or large natural fractures and vugs as found in limestones. This problem is critical as it increases the drilling costs due to wasted time, plus the possibility of stuck pipe and even losing the well. In most cases, viscous mud pills with lost circulation material, gel, etc, allow to temporarily reduce the losses but do not guarantee a durable plugging of the formation. Cement plugs can be used but their placement and the time necessary to drill through them make their use relatively costly.

The use of an internally activated silicate solution allows to obtain a solid free Newtonian solution with a very low initial viscosity. After a given period of time, which depends on the fluid design and the temperature, the viscosity of the solution increases rapidly to form a gel. This gel is coherent, strong, and does not develop free water as a function of time. The very low initial viscosity of this solid free fluid allows it to be pumped directly through the bottom hole drilling assembly, therefore saving time, and provides deep penetration of the final gel.

A high pressure experimental set up was used to plug various cores of different permeabilities and with different saturation fluids. Results are presented on the extrusion resistance obtained after one hour and after one week. This gel is shown to withstand differential pressures greater than 1500 psi per foot of plugged formation. Some results on the long term stability of this gel to aggressive brines, organic compounds and oil are included.

A case study of a job performed in Europe is also presented.

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