​Taking multistage fracturing technology to the next level

Packers Plus is moving into combined cemented-liner and ball-drop technology. Image: Packers Plus

The tight oil and gas revolution launched by advances in horizontal drilling and multistage fracturing has not stood still since it swept across North America after the turn of the century, racking up gains in production and falling costs.

Nor has the collapse in the price of oil crimped its advance—in fact in many ways it has only intensified the urgency to cut costs. Companies have dramatically reduced costs through a number of innovations, including ever-longer laterals and tighter fracture spacing.

Once known mainly for the open-hole, ball-drop fracture technology that has come to dominate much of the Canadian market, Packers Plus Energy Services has both improved that technology and diversified into such methods as cemented-liner completions in order to accommodate different demands by different companies operating in different plays.

Most recently, it has developed the StackFRAC HD-X (high-density) system specifically designed for extended-reach laterals that has many of the advantages of plug-and-perforate completions, without the drawbacks.

While a proven and mature technology, plug-and-perf completions in cemented-liner horizontal wells are inherently inefficient, Packers Plus explains in a recent white paper, Limited Entry Revolution. Plug-and-perf requires trips in and out of the well to detonate perforation charges and set bridge plugs for each stage, it notes, adding to non-productive time. It also increases the chances for problems to occur, such as wireline getting stuck when a bridge plug does not release or perforation charges not detonating, necessitating millout or abandoning of a stage. Additionally, plug-and-perf uses more fluid than other methods, adding to costs.

Cemented ball-drop completion systems typically require half the stimulation time or less than a plug-and-perf version. The Packers Plus white paper points to a study of the Eagle Ford shale that found completion times of five days for plug-and-perf compared to 1.6 days for ball-drop completions—more than three times faster.

Kevin Trahan, Packers Plus chief operating officer, estimates roughly half of the horizontal multifractured wells in Canada are completed open-hole and half are cemented; of the cemented, roughly 30 per cent are plug-and-perf and the rest are either ball-activated or coiled tubing–activated sleeves type systems. In the U.S., about 90 per cent of wells completed are cemented plug-and-perf.

“Packers Plus has been the largest player in Canada in the open-hole multistage fracking completion tool business, and it really drove the market in Canada to those types of systems—and had a great deal of success doing it,” Trahan says. “We were historically the biggest open-hole completion company for multistage frac tools, and what we are doing now is diversifying into the cemented-line completions.”

Plug and-perf completions do have their advantages, says Michael Mehle, Packers Plus fracture science stimulation engineer. “There are certain benefits to plug-and-perf completions, and we have been working hard on our systems to basically take the best of both worlds,” he says. “With the StackFRAC system, we have a very good limited-entry completion type without all of the inefficiencies of cemented plug-and-perf—and none of the downside of either [method] because we are both substantially increasing the stage count on the sliding sleeve system and maintaining our operational efficiency.”

Adds Mehle, “The system brings the ability to open multiple sliding sleeves with a single ball so that you can treat multiple stimulation intervals at a time, and there are many efficiency gains of doing so. It also makes possible essentially a perfect limited-entry frac.”

Limited entry is a means by which multiple fractures are created from a single stimulation using friction back pressure created in the wellbore by the ports or perforations. Operating like a garden hose fitted with a spray nozzle, with pressure increasing as the diameter of the opening is reduced, limited entry helps to distribute the flow evenly among the different fractures created on the single stage.

But in plug-and-perf completions, an explosive perforation is far from a precision-engineered hole, notes Mehle. “You don’t get exactly the size of hole that you planned on, and that in itself prevents the method from being very efficient—you wind up with imperfect flow distribution. And when you are pumping hundreds of thousands of pounds of sand, those perforations are sand blasted—they are rounded out and enlarged by the abrasion of sand going through them, so they don’t have a controlled geometry, which essentially defeats the concept of limited entry.”

Packers Plus QuickPORT IV sleeves, incorporating precision-engineered erosion-resistant nozzles reinforced with tungsten carbide, were designed to prevent perforation erosion, Mehle says. “We are able to put exactly the correct size of hole in, with the correct exit point size, so we can get exactly the right amount of back pressure to distribute flow evenly in a single stage. With that tungsten carbide insert it is essentially erosion proof, so during pumping of the job these holes don’t change size or shape and that initial flow distribution is maintained throughout the treatment.”

Packers Plus also re-engineered its ball and seat tools to enable them to increase the number of fractures per well as is increasingly demanded by the industry.

“We have entered the age of extremely large slickwater jobs, which has certainly put additional engineering requirements on the sliding sleeve systems because they are being exposed to more abrasion than at any time in the past,” says Mehle. “Conductivity is king in a lot of these oil plays. The more proppant that you are able to place, the more production you are able to get. We have got multiple operators right now putting 40 million pounds or more into a wellbore, which is probably a tenfold increase over past years.”

Being able to place very high proppant concentrations in the wellbore is generally a great benefit to a well, he adds. “That doesn’t necessarily mean you need to generate a gigantic frac job, it just means you need to do everything you can to put a high volume of proppant very near the wellbore, at the tail end of a fracturing stage. There is not so much focus today on creating fractures that are multiple miles long—there is more focus on close, near-wellbore conductivity.”

One of the traditional limitations of the sliding sleeve system is the need to incrementally increase ball seat diameter as larger balls are launched down the horizontal to activate progressive stages, limiting the system to roughly 50 stages, says Mehle.

By opening multiple sleeves with a single ball, Packers Plus is increasing the maximum number of fractures it can generate from a single wellbore. “If you can open three ports on each of those stages, you can now increase that stage count to 150. That gets us into the territory where we can compete head-to-head with cemented plug-and-perf in plays where fracture stage density is important.”

Additionally, the StackFRAC HD-X completion system incorporates an advanced seat and port activation design that enables smaller ball and seat increments to increase stage counts.

“We manufacture these sleeves with an erosion-resistant coating, which allows us to increment those ball seats with much smaller increments so we are able to push that stage limit to much higher. You need the erosion resistance because any small amount of erosion in that ball seat will cause the ball to just fly right through that ball seat. It’s taken some pretty difficult engineering to be able to do something like that and have pressure rating and reliability,” Mehle says.

The new tools have been living up to expectations in the field. In a case study in North Dakota’s Bakken Formation where an operator sought longer-reach laterals than the 35-stage ball-drop system it had been implementing, the operator ran the StackFRAC HD-X system in two wells with lateral lengths of roughly 9,700 feet. Using the non-standard ball seat sizes, it completed 49 and 50 stages with average stage spacing of 194 and 189 feet, respectively.

The first well was completed in 50 hours of pump time using 4.9 million pounds of proppant and 69,886 barrels of fluid, and the second well in 52 hours using five million pounds of proppant and 73,600 barrels of fluid. The company’s ePLUS Retina real-time downhole monitoring tool verified a 100 per cent success rate for ball launches, ball landing and sleeve shifting in the single, continuous pumping operation. After stimulation, wells can be immediately flowed back and put on production.

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