In an industry never short of challenges, dissolvable technology has adapted admirably. Today, it’s a common component of well completions, particularly effective in long laterals with higher stage density. A Stratview Research report even predicts that dissolvable frac plugs will be a $1.2 billion U.S. market in 2024.1
As laterals get longer and require additional stages, dissolvable plugs are becoming a necessity — the additional depth increasing difficulty of drill out. Challenges posed by horizontal sections have forced producers to quickly refine and innovate dissolvables.
Known as a tight reservoir, the Barnett Shale was a crucible for innovation in hydraulic fracturing. In the early 2000s, production began a sharp uptick, with sliding-sleeve technology the most popular completion method. It featured a progressive ball-seat system in which successively larger balls were dropped to activate a seat, opening up ports for hydraulic fracturing.
Soon, composite plugs were introduced. An improvement over cast-iron plug technology, the design still featured cast-iron slips that were difficult to drill out and remove from the wellbore. The coiled tubing procedure required for cleanout was costly. The process was also problematic, risky and time-consuming. The notion of a plug that would simply vanish, taking all of these problems with it, was still just an operator’s dream.
Use of composite plugs exposed the drawbacks to sliding-sleeve technology. High pressures would often lodge the balls into the seats, requiring drillout. In response, Magnum Oil Tools developed a dissolvable thermoplastic ball, revolutionizing sliding-sleeve technology.
Inevitably, this inspired the idea of a dissolvable plug. Quickly developed, the prototype passed American Petroleum Institute inspection on its first test and went into field trials. Within six months, Magnum had commercialized a product suddenly in high demand.
An early competitive advantage
Chemistry and temperature — those are the two primary variables considered when determining the right material composition for dissolvability in any given application. Most alloys used in today’s dissolvable plugs are magnesium-based, requiring that the operator understand the exact chemistry of the well fluid to predictably estimate how long it will take for that plug to dissolve.
However, downhole chemistry changes constantly. It varies dramatically from the vertical to the heel, and from heel to the toe. It varies from one well to the next, even on a multi-well pad. It’s affected by the original water source and the fluid being pumped into the well. With so many variables, predicting how long it will take for the plug to dissolve is complicated.
By contrast, the commercial version of Magnum’s dissolvable prototype — the Magnum Vanishing Plug™ or MVP — featured a thermoplastic material that dissolved according to downhole temperature, not chemistry. It’s consistent performance established early market dominance, branding the MVP a true market disruptor and proving the viability of dissolvable plugs.
When the MVP launched in 2014, operators were desperate to increase speed to production. Dissolvable technology became perhaps the most significant advancement since horizontal drilling. Conceivably, it could eliminate the need for coiled tubing, underscoring its economic advantage.
Innovations continued, as well services providers sought to further improve efficiencies. Today, the cost of producing a well is approximately 60 per cent of what it was in 2014. The price tag for dissolvables has also dropped, resulting in industry-wide acceptance — or almost.
The Permian problem, solved
Since 2013, the Permian Basin has been one of the world’s busiest and most lucrative shale plays. While the MVP performed exceptionally at temperatures above 175°F, it was not ideally suited for the relatively lower temperatures of the Permian.
In light of this challenge, Nine Energy Service, which had purchased Magnum Oil Tools in 2018, combined its engineering expertise with Magnum’s material knowledge to create a reliable dissolvable plug suitable for all temperature and salinity applications. The result was the Stinger™ Dissolvable Plug, which eliminated the need for a mandrel by using a wedge to set and hold pressure.
Six years after dissolvable technology became commercially available, the industry now has a plug with proven ability to convey to depth; anchor, seal, and deploy from the setting sequence; properly act as a barrier during multi-stage stimulation; and predictably degrade across a full range of wellbore characteristics.
Making sustainable profitable
Another advantage to dissolvable plugs is their promotion of sustainability. According to a recent environmental impact study, there is a significant and immediate reduction in greenhouse gas emissions when using a dissolvable plug versus a composite plug.2
Assuming a three-day coil tubing cleanout run, dissolvables reduce carbon footprint by 18 per cent or about 13.3 metric tons of CO2e. Dissolvable plugs that can circumvent intervention entirely reduce carbon footprint by 91 per cent, or roughly 67.3 metric tons of CO2e, over composites. On a six-well pad, this eliminates approximately 404 metric tons of CO2e, which equates to taking 84 cars off the road.
By improving site emissions, dissolvable plugs contribute to regulatory compliance. They also increase rate of return, as eliminating coiled tubing can save operators as much as 24 days per six-well pad in drillout time, reducing associated time, safety risks and service costs.
Innovations for 2020 and beyond
What’s next for dissolvable plugs? Like personal computers, the trend is miniaturization. The Stinger measures approximately 5.5 inches — much more compact than traditional dissolvables — vastly reducing the material to dissolve and debris to contend with.
As dissolvables become more ubiquitous, the need has grown for expert support in selecting the right plug for specific wellbore conditions. With low-temperature magnesium plugs, for example, manufacturers must maintain the material inventory to accommodate a variety of chemical fluid compositions. Smaller companies risk overpromising and overleveraging with inventories they can’t profitably maintain. Managing these variables and the attendant risks takes real engineering prowess.
To know the materials and ratios necessary for successful dissolution, savvy operators will seek increasingly detailed composition profiles detailing chloride content, suspended solids and fluid content from pump-down through return-to-surface.
Dissolvable plugs quickly evolved from innovative market disruptor to game-changing standard. Subsequent innovations have established their acceptance. It’s safe to say they’re here to stay.
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