Control of crosslinking reaction rate of aqueous fracturing fluids

Abstract

A method of controlling crosslinking reaction rate in a water based polymer fracturing fluid that involves using a mixture of a crosslinker, in combination with a crosslinking rate accelerator or a crosslinking rate retarder at a ratio such that the crosslinking reaction rate is controlled. This decreases the shear effects upon the polymer fracturing fluid during pumping which affects downhole stability of the fluid and decreases pumping and frictional pressures. The ratio of rate accelerator or rate retarder to crosslinker for a desired crosslinking reaction time is dependent upon pH, surface temperature, polymer concentration, salt concentrations, fluid loss additives, surfactant types and concentrations, mutual solvents and alcohol. The preferred polymer fracturing fluid is a high pH aqueous salt solution including a hydroxypropyl guar polymer. The preferred crosslinkers are transition metal chelates. The preferred crosslinking rate accelerators are polyamines. The preferred crosslinking reaction rate retarders are glyoxal and triethanolamine. Batch mixing of the polymeric fracturing fluid, crosslinker and rate accelerator or rate retarder is possible; however in the preferred embodiment the crosslinker and accelerator or retarder are injected simultaneously with the polymeric fracturing fluid so that the crosslinking reaction rate can be continuously adjusted in response to changing conditions.