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Time to Return to the Low Pumping Rates in the Fracture Stimulation of Unconventional Reservoirs


 To maximize hydrocarbon fluid recovery and economics in a challenging environment of ultralow permeability, an aggressive stimulation strategy is typically proposed. It was designed to reduce the completion or stimulation cost and time by placing multiple perforation clusters (typically three or more clusters per stage) and performing fracture stimulation by pumping the fluid/proppant system at very high rates to generate the necessary differential pressure and multiple fractures per stage.
 Because the stimulation pump rate in unconventional reservoirs is typically a function of the number of perforation clusters, number of perforations per cluster, the entry hole diameter of the perforations, and a fixed required minimum rate per perforation, the resulting typical pumping rates to perform fracture stimulations to generate more than one fracture per stage is in the range of 60 to 100 bbl/min or higher. However, historically, the fracture stimulation of multiple perforation clusters performed at high pumping rates often resulted in almost 80% completion efficiency as documented by Wheaton et al. (2016). Therefore, during each stage, single or multiple perforation clusters might not be fractured or marginally stimulated, and thus do not contribute to well production.
 To improve the typically observed completion efficiencies in recent years, continuing with the strategy of high treatment rates, self-soluble solid particle systems have been introduced in unconventional reservoir stimulations as an effective diversion system. The same system has been also used during refracturing operations or to increase the number of clusters per stage. This technology has been effectively deployed in the field and has provided value.
 Discarding fluid and proppant logistic issues, the high treatment rate requirement for unconventional reservoir fracture stimulation demands the availability on location of high-pressure pumping equipment with very high horse power, which is available in North American operations, but not generally in most international operations. This limitation was addressed as much as possible using the available equipment or by limiting the completion strategy.
 To help improve low completion efficiency in unconventional reservoirs, fracture stimulation, and the generation of at least one fracture per perforation cluster, particularly in locations where high-pressure fracturing equipment availability is limited, this paper suggests that the industry return to the conventional low pumping rate fracture stimulation treatments combined with the use of the self-degrading solid diversion systems (SDSDS) to maximize the generation of at least one fracture per perforation cluster.