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guar gum

1. n. [Drilling Fluids]
A hydrophilic polysaccharide from the seed of the guar plant. It is a galactomannan type of saccharide that is highly dispersible into water and brines of various types and salinity. Its water solutions are non-Newtonian and also can be cross-linked by borax to give very high gel strength for suspension. Such a structure is easily broken by breakers in fracturing fluids, so it serves as a carrier for placing sand far back into fractures. It is also used as a top-hole drilling fluid. Disadvantages of using guar gum include its lack of thermal stability and sensitivity to high pH and bacterial fermentation.