Various types of breaker systems are used for viscosity degradation of fluids in fracture stimulation operations. Achieving improved fracture conductivity is one of the key advantages of using effective breaker systems, but there could be an increased risk of poor proppant placement and premature screenouts resulting from early viscosity reductions as the fluid is exposed to temperature. To resolve this issue, a controlled release of the breaker over a period of time is very desirable.This paper highlights the controlled release of encapsulated oxidizers and chelating types of breakers that are effective in bottomhole static temperatures (BHSTs) up to 275°F. Oxidizers without encapsulation begin to decompose fluids at low to moderate temperature, which can lead to a rapid decrease in gel viscosity before completion of the fracturing operation. Neat chelating breakers can absorb the crosslinker rapidly; thus, little to no crosslinking action would be present, even at moderate temperatures. A newly developed encapsulant makes oxidizers and chelating agents viable for reducing the crosslinked viscosity gradually with temperature.The new encapsulant is a blend of selected polymers that release the active breaker through diffusion. It is possible to optimize the release rate of a breaker by simply adjusting its ratio in a polymer blend. The controlled release of a breaker through an encapsulant was evaluated at 200°F under static conditions. The dynamic rheology of fracturing fluids was also studied as a function of encapsulated breaker concentration in temperatures up to 275°F. The results derived from this investigation are of significant importance to the oilfield industry.

Aliphatic polyesters containing pendent unsaturation were synthesized by the polycondensation of a diol, dicarboxylic acid and glycidyl methacrylate. Grafting methacrylic acid (MAA) resulted in graft copolymers containing polyester backbone and MAA grafts. Depending on composition, the polymers swelled extensively and eroded or dissolved at near neutral pH but remained in collapsed state at acidic pH. Three representative drugs differing in solubility, viz., Diltiazem hydrochloride (DH), Indomethacin (IM) and Verapamil hydrochloride (VH) were released at constant rate from tablets made by compressing spray-dried microparticles. The release of DH at constant rate has been attributed to increase in diffusion coefficient of the drug from the swollen layer of matrix. The release of IM and VH at constant rate was governed by erosion and was enhanced in matrices which undergo dissolution. The release rate was enhanced with increasing MAA content and the frequency of grafts along the polyester backbone. Once a day dosage forms for drugs differing in solubility have been developed using a single polymer matrix which is easy to manufacture.