Since the beginning of the U.S. shale revolution, operators have been frustrated by rapid production decline rates, nonproductive frack stages, extremely low recovery factors and high opex.

Ironically, the underlying causes of these frustrations can be traced back to hydraulic fracturing, which has been cited, along with horizontal drilling, as a key enabler of the shale revolution. Like all liquids, hydraulic fracturing fluids tend to follow the path of least resistance. This frequently leads to erratic fluid and proppant placement, which can result in overtreated zones, fractures growing into undesired zones, untreated perforation clusters within a stage, suboptimal reservoir contact and the inability to create the desired level of complexity in the fracture network.

Diverter technology
In the past, commodity diverter materials such as gilsonite, rock salt, benzoic acid flakes and bio-sealers often were deployed to block the path of least resistance and redirect fracturing fluids to the perforation clusters where they are needed for maximum stimulation performance. To perform effectively, these diverter materials must remain intact throughout the fracturing operation to create the desired “barrier,” then dissolve after the operation is completed to permit production flowback to the well.

More recently, specially engineered solid particulate diverter systems have been developed with optimal particle size distribution and longer dissolution times. In addition, these newer diverters help enable far-field diversion, which creates more complex fracture networks by temporarily plugging the main fracture to allow the fluid and proppant to extend into the far—and smaller—reaches of the fracture network. However, one challenge that has remained is that the dissolving diverters create voids in the proppant pack that can close or “choke” the fracture in the near-wellbore area and restrict production.

Newest advancement
The latest advancement in diverter technology is a solid particulate diverter and ultralightweight proppant combination known as REAL Divert Complete that is engineered to deliver effective, efficient diversion without risking collapsed or choked hydrocarbon pathways. Superior conductivity is enabled by premixing an engineered solid particulate diverter with a specially engineered strong but lightweight proppant and placing it into the fracture area.

The system’s diversion materials are fully degradable and soluble, so they clean up completely after the stimulation treatment. The ultralightweight bimodal proppant is engineered to have large particle size distribution, which makes the diverter more efficient. Once the diverter particulates dissolve, the proppant particles keep the fracture open to maintain a permanent connection between the near-wellbore and far-field areas of the fracture network and to allow unrestricted hydrocarbon flow throughout the life of the well.

Improving production
With increased reservoir contact and more effective stimulation of perforation clusters, production and ultimate recovery are improved. For example, an operator in the Bone Spring Shale in New Mexico significantly improved production over offset wells using the new family of diverter technologies.

The operator was dissatisfied with initial production rates and recoveries from multistage hydraulic fracturing of offset horizontal wells in the field. Information gathered from production logging, microseismic and other monitoring
methods showed that not all frack stages were contributing to total production. A key reason was that some perforation
clusters in each stage had been either ineffectively stimulated or not stimulated at all. It is believed that there were two primary contributors to the inconsistent fracture pattern and the resulting poor performance along horizontal laterals. First was the heterogeneous nature of shales. Second was a phenomenon known as imparted stress shadowing. This phenomenon occurs when two hydraulic fractures are placed adjacent to one another and the presence of one frack impacts the stress experienced by the other.

The new solid particulate diverter was used to treat a new well with 10 planned frack stages and five perf clusters per stage. The treatment effectively stimulated the perf clusters by providing more even distribution of the fracturing fluid and proppant. During the first six months of production, the treated well’s cumulative production was 54% greater than the offset wells.

Economic benefits
Diverter systems such as the one described in this article help accelerate stimulation operations by enabling the placement of more perforation sets per stage, combining stages and reducing the number of plugs required for isolation. In addition to improving initial production rates in new conventional and unconventional wells, these diversion technologies can help rejuvenate mature wells through effective refracturing treatments.

The economic benefits of the latest diverter technology in this application are illustrated by a case study in De Soto Parish, La., where production from six wells increased between 8% and 2,271% following the restimulation treatment. An operator in this section of the Haynesville Shale had a large inventory of previously drilled unconventional wells that were reaching the low end of the production curve. The operator wanted to refracture the existing wells to avoid the cost of drilling and completing new wells.

It was determined that the diverter for the restimulation would need to be stable enough to withstand the 150 C (300 F) bottomhole temperatures found in the Haynesville for up to 16 hours—the estimated amount of time needed to complete retreatment. To treat underperforming intervals and reestablish wellbore connectivity through pre-existing fractures, a specially formulated high-temperature diversion agent was pumped between frack stages. Engineers on location closely monitored the job and adjusted the volume of diverter as needed to control the pressure responses for each treatment stage.

The constant monitoring and adjusting of pump rates and fluid selection kept pressure, fluid and diverter responses under control. Restimulating with diversion technology resulted in savings of $7 million per well by eliminating the need for drilling and completing replacement wells. It also enabled the operator to effectively restimulate more of the lateral section, increasing
EUR. Based on these results, the rejuvenation program has grown from a six-well pilot to a 15-well program, with 70 additional wells in line for rejuvenation.

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