SPE Members
In high pH, low temperature fracturing fluids, enzymes are not useful breakers because enzymes are not active in high pH solutions. When these types of fluids are used, oxidizing breakers are used in Conjunction with activators to break water-based fracturing fluids. A delayed release oxidizing breaker which it's operable temperature range is between 70 - 125 F has been developed. This breaker is useful in delaying the break of high pH, low temperature fracturing fluids. Improved fluid rheology in the applicable temperature range was also attainable with this product. Filter cake dissolution studies pointed to the usefulness of the delayed release product in cleaning filter cakes of borate fluids. This product will allow the breaker concentration to be increased over the amount of conventional breaker currently added. This will lead to improved fracture cleanup. Actual field trials made in a Belridge Field study suggested that improved performance of borate fluids in the low temperature zones was attainable. Using a borate fluid with the delayed release breaker added allowed more sand to be placed in the fracture and increased cumulative oil production.
In many fracturing treatments the ultimate permeability which could result is not fully realized. Further, actual production increases do not usually match predicted production increases, even with recent improvements in fracturing simulators. One growing area of research in hydraulic fracturing as a result of these conditions is in fracture conductivity damage caused by fracturing fluids and the resulting flow impairment. It has also been reported that the fracture conductivity studies can improve the design of fracturing treatments. The accepted cause of fracture conductivity impairment is incomplete cleanup of fluid contained in the proppant pack and filter cake deposition on the fracture face. This damage is formed by concentration of the gelling agent in the fracture caused by fluid leakoff.
Two remedies to this problem have been reported. Elbel et al have reported that increased breaker concentrations can improve proppant pack cleanup. Norman et al have reported the successful development and application of a post fracturing treatment which improves fracture cleanup. The only drawback of this system is that it is a post fracturing treatment, therefore, complete contact in the fracture cannot be assured. An improvement in this system would be the development of a delayed release version of this system which would allow addition directly to the fracturing fluid to assure complete fracture contact.
The concept of delaying the release of fracturing fluid additives has been theorized for sometime, but not until recently has this concept become practical. Gulbis et al have reported the successful development of an encapsulated oxidizing breaker. This breaker has allowed breaker concentrations to be increased, improving fracture conductivity. They reported that the coating applied to the breaker allowed the release of the breaker by crushing upon fracture closure, a concept originally conceived by Note. Other methods of delayed release have also been reported. Cantu and Boyd have reported the use of a degradable polymer which releases an acid into the fracturing fluid. A combination complexing agent and breaker which slowly releases into the fracturing fluid based on a chemical reaction has also been reported by Brannon and Ault.
A more reliable approach may be application of a coating over the additive which should allow the additive to be slowly released by leaching through the coating. A release mechanism based on formation closure may be impractical, since the pliability of the coating at bottomhole conditions or low closure pressures may not allow the encapsulated breaker to be crushed upon formation closure. Delayed release breakers which are dependent on chemical reactions or degradation may be limited in the applications where they can be used.
P. 359^
