An efficient system of running gelled diesel stimulation fluid has been developed which allows continuous treatment and requires no pregelling or batch mixing. Continuous gelling while pumping is possible with this unique system, which is a combination of phosphate ester chemistry and computer-controlled metering incorporated in a mobile trailer or preblender. Operational and environmental advantages have been reported after field applications of this system.
Stimulation treatments using gelled oil as the fracturing fluid have been routine for many years. Most of these treatments have been performed by batch mixing gelled oil in storage tanks before pumping it into the formation. This, however, can result in costly waste of premixed gel should the job be cancelled or terminated prematurely. The system discussed in this paper gels the fracturing fluid while it is being pumped downhole, to eliminate the disposal problems associated with batch mixing;
The preblender is capable of mixing at 10 to 40 bbl/min and metering two liquid additives (phosphate ester gellant and activator) into the diesel. The automated equipment can be used to vary the concentrations of the additives, gel viscosity, or job volume in realtime at any point during the job without wasting gel.
Environmental and operational advantages of running gelled diesel continuously include (1) no left-over gel in tank bottoms to dispose of after the job, (2) pre-gelling time saved, (3) operators pay only for materials actually used during the job, and (4) elimination of the difficult task of withdrawing highly viscous, batch-mixed gels from storage tanks.
In Alaska, several wells have been hydraulically fractured using the technique. The diesel-based gel is found to be preferable to water-based gel systems in areas where temperatures can reach well below the freezing point. The equipment of this system is also designed to withstand arctic conditions.
This paper describes the fluid system as well as the equipment design and metering criteria for the continuous gelled oil system. Field application cases of this system will also be presented.