An Improved Encapsulated Breaker To Decrease Hydrostatic Release and Increase Thermal Stability

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractEncapsulating oxidizers with impermeable coatings is a wellknown method for delaying the viscosity reduction of a fracturing fluid. It also enables the concentration of oxidizer breaker in fracturing fluid filter cakes formed during the leakoff and fracture closure process. The oxidizer is released by crushing the encapsulated particles during closure, but some oxidizer is also released before closure through a combination of hydrostatic release and mechanical abrasion. This paper discusses the effect of the particle coating thickness on the hydrostatic release mechanism. Tests were conducted on encapsulated oxidizers with varying coating thickness to determine release rates at temperatures ranging from 175 to 250°F using a specialized oxidizer breaker release apparatus. The coating thickness required to minimize hydrostatic release was identified.Analysis of both active and inactive oxidizer species during the hydrostatic release experiments also enabled the determination of the effective oxidizer breaker lifetime. Because oxidizers are designed to decompose into free radicals (the molecules responsible for polymer molecular weight degradation), shielding the oxidizer from the hightemperature environment extends the oxidizer breaker lifetime. We show that the encapsulation process is able to protect an otherwise unstable molecule from thermal and hydrolytic decomposition and the extent of the protection is related to the coating thickness.The information obtained from this study was coupled with rheology experiments to validate breaker performance at temperature for a new thicker-coated oxidizer. The benefit of this material is increased concentration of active oxidizer breaker downhole, which facilitates fracture fluid cleanup and improves fracture conductivity and half-length.