More rig time means higher expenses, less profit and production delays—especially in challenging horizontal plug-and-perf (PNP) operations. Using an optimized fracturing plug is critical for complete zonal isolation during stimulation. Frack plugs play an important role in expedient well completion and enhanced hydrocarbon recovery. In the current market conditions in which margins are increasingly compressed, frack plugs need to perform reliably and efficiently in diverse wellbore conditions.

Challenges with metallic plugs

There are three main challenges associated with the deployment of frack plugs, particularly in unconventional wells. These challenges include running the plug into the wellbore at faster speeds without the tool presetting; achieving the necessary anchoring force and a high-integrity seal to prevent leaks; and milling the plugs out as quickly as possible with minimal cuttings to avoid getting stuck with the milling assembly, hindering production flow or plugging surface equipment. When these scenarios occur, the well likely requires interventions, which amounts to higher costs and delays.

Traditional composite plugs typically contain higher amounts of cast iron or other metals in the slips. Although durable in a range of downhole conditions, traditional plugs often fail to provide efficient run-in and mill-out. Because of the high metallic content, these plugs are heavier and travel more slowly in the wellbore.

Composite plugs with primarily metallic slips leave larger debris in the wellbore, which makes milling operations more complex, lengthy and costly. Additionally, these plugs tend to be longer, which makes them more difficult to use in deviated wellbores. This also increases the amount of material that must be milled out across multiple zones per well.

To overcome these limitations, the solution is to install a composite plug with fewer metallic components and a shorter length.

Optimized solution

Weatherford introduced the TruFrac composite fracturing plug to address the specific challenges that operators experience when using other plugs. The plug contains a higher amount of composite than other comparable plugs on the market.

Developed and manufactured by Weatherford, the plug is made from a proprietary in-house blend of 97% high-strength composite to reduce the weight of the plug and minimize the metallic content. The lightweight composite enables these plugs to achieve run-in speeds of 152 m/min (500 ft/min) as well as easier, more efficient milling.

Because the composite is highly durable, the plug is rated for use in diverse environments with temperatures up to 149 C (300 F) and pressures up to 10,000 psi. This material also produces small, lightweight cuttings that can be easily removed from the wellbore for a cleaner well.

Progressive design

The TruFrac plug combines innovative composite material with upgraded design elements: field-proven slip technology and an advanced molded-element system.

Although lightweight, the design and construction of the plug provide enhanced performance. The slip systems deliver an anchoring force with the lowest amount of metal possible. The upper slip and cone are machined from a single piece of filament-wound composite and incorporate powdered metal buttons to provide the necessary anchoring force and improved milling results. The lower slip and cone use a combination of composite and small, soft cast-iron inserts.

During mill-out, this avoids the breakage, spinning and mill damage that harder, more brittle materials can inflict. Additionally, the lower cone is faceted to prevent spinning during mill-out. The bottom of the plug is also beveled to provide additional protection against spinning and to act as a clutch during mill-out.

The molded-element system has a smooth outside diameter that enables high run-in speeds with a significantly reduced risk of plug components becoming caught on lips in the wellbore and presetting. The smooth surface prevents fluid flow from causing the element to flare and become stuck in the wellbore. Once set at total depth, the element provides a reliable seal even in tough downhole conditions. The robust backup system ensures the element does not extrude while holding against high pressures.

In addition to its light weight, the short length of the plug adds to efficient, cost-saving performance. The TruFrac plug is a sleek and compact tool that can easily navigate tight turns and doglegs.

Versatile performance

With composite construction and an optimized design, these plugs perform in any type of wellbore in diverse downhole conditions. These plugs can stimulate a single zone or multiple zones in vertical, deviated, horizontal or multilateral wellbores.

The plug is available for 4.5-in. and 5.5-in. casing sizes with a choice of two ball deployments: internal ball and top ball. The internal-ball design eliminates the need to drop a ball from the surface, and the top-ball design provides a larger flow area for higher return rates. Operators have the flexibility to choose the size and options.

Case study: 10- to 15-minute mill-out times

An operator in the Permian Basin sought to significantly decrease its time on location during the mill-out phase of a PNP operation. Previously, more traditional plugs had been used. From May to December 2014, the operator installed 619 TruFrac plugs in 27 Permian wells. The 5.5-in. plugs were run in 5.5-in. 20-lb/ft casing. Each well had 20 to 32 zones to isolate and, on average, 3,048-m (10,000-ft) laterals and total-depth temperatures of 65 C (150 F).

Using stick pipe with a rock bit to drill out the plugs, the operator achieved an average mill-out time of 10 to 15 minutes per plug. Compared to the traditional plugs, the TruFrac plugs saved a minimum of 10 minutes per plug, or more than 100 hours of total milling time.

With the reliable and efficient performance of this plug, operators can reduce the amount of time needed for PNP operations as well as decrease the number of operations required to frack multiple zones in the same well. The plug can also help prevent operational delays and begin production sooner. In doing so, the plug can have an impact on completion costs—which make up the largest portion of the average well budget—and can benefit overall well economics.