Hydrophobic guar gum derivatives prepared by controlled grafting processes for hydraulic facturing applications

Abstract

The synthesis of new water soluble guar gum derivatives is described. Introduction of polyalkoxyalkyleneamide grafts to guar gum or hydroxyopropyl guar was achieved in a three step process: carboxymethylation with sodium chloroacetate, esterification with dimethyl sulfate and amidation with a series of polyalkoxyalkylene-amines. The process steps were followed using infrared spectroscopy; the grafted guar derivatives were characterized using FT-IR and 1H NMR. A series of hydroxypropyl guar derivatives with degrees of carboxymethylations ranging from 0.15-0.25 were modified with polyalkoxyalkyleneamines with molecular weights ranging from 300-3000. The ratio of oxypropylene to oxoethylene units in the polyalkoxyalkyleneamines was varied from 9/1 to 8/58 to adjust the hydrophobicity of the grafts. In addition, predominating hydrophobic grafts from the same family were produced. The percent grafting of the isolated products were in the range of 0.03 to 28 percent depending on the type of guar gum derivative and polyalkoxyalkyleneamines used. The grafted derivatives were evaluated for hydraulic fracturing application in oil industry. The viscosity properties of the grafted derivatives were compared with the parent carboxymethyl and carboxymethylhydroxypropyl guar gum. Aqueous solutions of the graft copolymers exhibit viscosities one to two orders of magnitude lower than corresponding solutions of the parent materials. The aqueous solutions of the graft copolymers when crosslinked with zirconium crosslinking agent at high pH; exhibited comparable or better viscosity properties to the crosslinking solutions of parent materials. To facilitate the clean up process the crosslinked fluids were treated with an enzyme breaker system. The viscosity of the resultant fluid after the treatment was very low. The degraded parts of some of these derivatives with hydrophobic grafts created emulsions when extracted with toluene.