Superabsorbent refers to a water-swellable, water-insoluble, organic or inorganic material capable of absorbing at least about 10 times its weight and up to about 30 times its weight in an aqueous solution containing 0.9 weight percent sodium chloride solution in water. A superabsorbent polymer is a crosslinked polymer which is capable of absorbing large amounts of aqueous liquids and body fluids, such as urine or blood, with swelling and the formation of hydrogels, and of retaining them under a certain pressure in accordance with the general definition of superabsorbent.
The superabsorbent polymers that are currently commercially available are crosslinked polyacrylic acids or crosslinked starch-acrylic acid graft polymers, in which some of the carboxyl groups are neutralized with sodium hydroxide solution or potassium hydroxide solution. As a result of these characteristic properties, these polymers are chiefly used for incorporation into sanitary articles, such as babies' diapers, incontinence products or sanitary towels as well as industrial applications such as coatings for cables, for use in well borings and superabsorbent polymers in solvent based pastes.
U.S. Pat. No. 5,817,713 discloses superabsorbent polymer dispersed in polyvinyl chloride plastisol using an organic solvent. U.S. Pat. No. 6,013,325 discloses a swelling paste made of an admixture of an aqueous solution of a water-soluble polymer and at least one multifunctional alcohol as crosslinker and thickeners. U.S. Pat. No. 6,380,298 is directed to superabsorbent polymer coatings for fiber reinforced articles where in water-soluble superabsorbent polymer is used in conjunction with a binder resin. U.S. Pat. No. 6,488,999 is directed to a printable superabsorbent polymer label coating including a superabsorbent coating comprising a gelatinous material, a cross-linking agent and water.
Drilling fluids or drilling muds as they are sometimes called, are slurries of solids used in the drilling of wells in the earth for the purpose of recovering hydrocarbons and other fluid materials. Drilling fluids have a number of functions, the most important of which are lubricating the drilling tool and drill pipe which carries the tool, removing formation cuttings from the well, counterbalancing formation pressures to prevent the inflow of gas, oil or water from permeable rocks which may be encountered at various levels as drilling continues, and holding the cuttings in suspension in the event of a shutdown in the drilling and the pumping of the drilling fluid.
For a drilling fluid to perform these functions and allow drilling to continue, the drilling fluid must stay in the borehole. Frequently, undesirable formation conditions are encountered in which substantial amounts or, in some cases; practically all of the drilling fluid may be lost into the formation. Drilling fluid can leave the borehole through large or small fissures or fractures in the formation or through pores in the rock matrix surrounding the borehole.
U.S. Pat. No. 4,635,726 discloses a slug of superabsorbent polymer dispersed in hydrocarbon fluid used as additives for drilling fluids. U.S. Pat. No. 6,581,701 discloses methods for reducing lost circulation in well bores using the gel forming and water swellable polyacrylamide polymer that swells at a rate slow enough to reach the lost circulation zone of a well before those polymers have swollen to an extent that disrupts the drilling process.
It is therefore an object of the present invention to provide an aqueous superabsorbent polymer paste for use with substrates to enhance the properties of the substrate such as absorbency. Yet another object of the present invention is to provide an aqueous superabsorbent polymer paste for use with drilling fluids to enhance the properties of water retention and slug expansion for reducing lost circulation in well bores.