Development and Performance Evaluation of a Boron-modified Nanosilica Crosslinking Agent

Field application of guar gum fracturing fluid treated with organoboron and inorganoboron crosslinking agents has been faced with problems such as large amount of guar gum consumed and high residue content of the fracturing fluid. In laboratory research on these problems, nanosilica was first made by the hydrolysis of sodium silicate, and the nanosilica made was then reacted with γ-aminopropyltrimethoxysilane to produce a surface modified nanosilica. The surface modified nanosilica was further reacted with boric acid to produce a boron-modified nanosilica crosslinking agent with particle sizes between 7 nm and 11 nm, and it was able to effectively reduce the amount of guar gum required in mixing fracturing fluid and the residue of fracturing fluids. Study was done on the performance of a hydroxypropyl guar gum fracturing fluid treated with the boron-modified nanosilica as a crosslinking agent, and it was found that the fracturing fluid had good properties. At temperatures 50℃ and 120℃ respectively, shearing of the fracturing fluid at 170 s^-1 for 120 min produced a fracturing fluid with viscosity of greater than 50 mPa.s. At 50℃, after gel breaking for 60 min, the fracturing fluid had viscosity that was less than 5 mPa.s and surface tension of 22.77 mN/m. Core swelling test with the gel-broken fracturing fluid showed that the percent core swelling was 89.6% and the residue content was 145 mg/L. Permeability impairment of a core matrix tested with the fracturing fluid was between 9.82% and 14.86%. Other properties of the fracturing fluid were all satisfactory, the amount of hydroxypropyl guar gum required for mixing fracturing fluid was reduced by 20%, and the residue content of the fracturing fluid mixed was reduced by 25%, satisfying the needs of field operations.