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`THE LATEST ISSUE
`Open-Hole Or Cased And Cemented
`Weighing the pros and cons of completion choices for multifrac
`horizontals
`[Print Article: November 2011, by By Pat Roche] As the use of multiple fracture
`stimulations in horizontal wellbores skyrocketed in recent years, a debate
`emerged over the best completion method: open-hole ball drop or cased and
`cemented holes?
`
`It boils down to a question of whether mechanical packers or cement provide the
`best means of isolating between frac stages during multiple completions in
`horizontal wellbores.
`
`Murray Reynolds, a veteran completions engineer with TAQA North Ltd., looked
`at the advantages and disadvantages of each system in a presentation at an
`Infocast tight oil conference in Calgary in September.
`
`The open-hole ball-drop system is typically associated with Calgary-based
`Packers Plus Energy Services Inc., though a number of competitors also run
`similar systems. A packer is set in the external casing, uncemented. In the case of
`the Packers Plus StackFRAC system, balls made of thermal-plastic material such
`as Teflon are dropped into the well to shift a sleeve, isolate the previous frac and
`open the next frac port up-hole.
`
`Other open-hole systems use a dart instead of a ball to shift the sleeve. Others
`use swellable packers where an elastomer element reacts with the wellbore fluid
`or temperature to expand, thus creating a seal with the open-hole. Depending on
`conditions, it could take a week or more for these to be set up in a wellbore before
`a frac operation begins.
`Most of the fractured horizontal well completions in western Canada use open-
`hole packer-based systems, which may be the cheapest option.
`
`The Barnett shale is currently almost 100 per cent cased and cemented.
`Reynolds noted that early experiments with open-hole gave poorer results from
`the standpoint of microseismic monitoring as well as production performance.
`On the other side of the debate are the advocates of fully cemented liners. These
`wells are typically more expensive ¿to complete, but allow maximum control of
`fracture placement, providing there is good ¿cementing in the horizontal section,
`which can sometimes be a challenge.
`
`Listing the pros and cons of each system, Reynolds said the big advantage of the
`open-hole packer system is that it's a ¿continuous frac process. It can be done
`quickly if logistics allow everything to be located on site. "If you're pumping
`100,000 kilograms per fracture stage, you might not be able to do it all in one
`day," he said. "But generally...you can do 15 fracs in a day, or more."
`
`6/24/2015
`
`Open­Hole Or Cased And Cemented
`
`http://www.newtechmagazine.com/index.php/news/archived­articles/1853­open­hole­or­cased­and­cemented
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`
`NEW TECHNOLOGY MAGAZINE SUPPLEMENT
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`MULTISTAGE FRACKING 
`AND HORIZONTAL DRILLING
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`FOUNDATIONS MAGAZINE
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`PRESCRIPTION FOR PROGRESS
`
`Other advantages include high pump rates and the fact that there's no frac fluid or
`proppant limit. Also, Reynolds said open-hole completions may enjoy a slight cost
`advantage over cased and cemented wells.
`
`On the downside, one of the disadvantages of open-hole ¿systems is the
`number of frac intervals has historically been limited to about 24 stages. ¿"But
`now multiplier systems ¿are becoming available where we can frac up to 60
`stages," ¿so there may be fewer limits ¿in the number of stages, Reynolds
`conceded.
`
`Open-hole systems have less control over frac length and frac placement, he
`said. "In tight oil, as in tight gas, fracture half-length is everything." Frac ¿half-
`length refers to the radial distance from the wellbore to the outer tip of a fracture.
`Also, he said setting the hydraulic packers may create frac initiation points.
`
`If the balls aren't recovered, the operator may need to mill out the balls and seats,
`adding significant cost. However, Reynolds noted one vendor has retrievable
`ball/seat assemblies.
`
`Looking at the pros and cons of the cased and cemented systems, Reynolds said
`two big advantages are longer fracs and more control over where each frac
`initiates. He believes one of the biggest future innovations of cemented
`completions will be the opportunity to use cemented frac ports, which can be
`shifted with a ball or coiled tubing.
`
`"This is, I think, the future. We've run a couple of these. [We've had] very good
`results in terms of fracture placement and productivity," he said about cemented
`frac ports, which he called a "potential breakthrough technology for cemented
`completions."
`
`He said cemented frac ports are currently being used in relatively shallow
`applications such as in Viking tight oil in Saskatchewan.
`
`Other new technologies for cased-hole frac isolation include composite bridge
`plugs that can be easily milled out. Reynolds said Halliburton Energy Services
`has a self-removing bridge plug that can be set on a timer to explode into a pile of
`ceramic dust-"a really good way to remove bridge plugs."
`
`On the downside, it takes ¿longer to frac the same number of intervals in a
`cased and cemented well than in an open-hole well. This is because of the time it
`takes to perforate and the fact that it isn't a continuous process.
`"People who are looking strictly at cost are going to probably stick with ball-drop
`systems," Reynolds said. But if the operator and its service companies are adept-
`and don't encounter any problems that extend the operation-the cemented
`completion "can be cost competitive," he added.
`
`In some cases, reservoir conditions may dictate the use of cased and cemented
`completions. In the Horn River, for example, packer systems can't withstand the
`high temperatures.
`Reynolds said many innovative tools and techniques are emerging that he
`believes have the potential to change the way multi-fractured horizontal wells are
`completed in the future. "Hang onto your hat-there's a lot of technical innovation
`going on," he said.
`
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`Open­Hole Or Cased And Cemented
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