A new perforating and fracturing method for multiple pay zones can double production.
Phil Snider has been at Marathon Oil 22 years, a mighty long time at a single company in this business. A distinguished lecturer for the Society of Petroleum Engineers (SPE), Snider travels the world giving a presentation titled "Casing-Conveyed Perforating Systems for Multi-Zone Stimulations to Improve Well Productivity."
I had the opportunity to hear him give that speech at the Rice University and University of Houston joint SPE student chapter meeting, and I thought the new methods he described were worthy of entry in Hart's E&P's Meritorious Engineering Awards competition. Snider said the various technologies used in that perforating system had indeed been entered 2 years in a row and had not won in the perforating category. Well, I thought they at least merited some ink, so I'm going to share what I learned with my faithful readers.
Old way doesn't work well
Buddy Woodruff of Protechnics did a thorough study of staged perforation and stimulation jobs in which several pay zones were perforated and fractured at the same time. Of 1,647 wells, 880 had one or more opportunities for improvement (unstimulated intervals, understimulated intervals), and 30% of the wells had low-pressure zones that took all the fluid. Wouldn't it be great if you could perforate and fracture each layer individually without having to trip in and out of the well for each one or drill out the bridge plug that separates each stage?
Enter external casing perforating, or Excape. Marathon holds the patent on this technology, which puts the perforating guns outside the casing. "This is more than thinking outside the box," Snider said, "It's thinking outside the casing - a whole new paradigm in the perforating world." The hydraulic control lines that actuate the firing heads are laid in a slotted collar outside the casing to protect them from the rock. A flapper isolation valve closes when the gun is activated to isolate each interval. Each perforating gun can be set to explode at a certain pressure, so a hydraulic hand pump can be used to increase the pressure and set off a succession of guns for each interval.
Tests of this technology have been conducted in Canada, Wyoming, Oklahoma, Alaska and Louisiana for Marathon, Phillips and BP. BJ Services, CoreLab and Tripoint - instrumental in the technology development - provided the equipment and services. "We developed this technology with people I've known for years and trust a lot. It took these people less than a month to design and build it," Snider said.
Results were impressive:
• 60% to 80% reduction in completion time;
• 20% lower costs; and
• 50% improvement in well productivity.
The net present value of one well went from US $2.5 million using conventional completion technology to $6 million using Excape. Another well cut $250,000 in costs and 35 days off completion time as a result of using this process. "Perforating operations that used to take a day only take 10 minutes. On one job, 12 fracs were completed in 13 hours. It used to take 30 days," Snider said. Production doubled compared to offset wells. For four of the wells perfed with this system, two wells produced the same, and one well had 50% improvement.
Marathon's Technology Organization has made an unprecedented offer to its operating regions: It will turnkey a well using Excape for 50% of the incremental value obtained after the job. "Before, we were not effectively treating some zones, and production was being missed. It's kind of criminal to leave all that production behind," Snider said. The jobs to date have used 31/2-in. casing, but a 41/2-in. system has been designed and a 27/8-in. system has been built. One of the lessons learned during the testing was that actual bottomhole pressures could vary ±3,000 psi compared to calculated values, so downhole pressure gauges are invaluable for real-time pressure monitoring.
Another key to this new method is understanding the relationship between pipe measurements and openhole logging depths so that the perforating guns are placed at that depth. As many as 15 modules have been placed at the correct depth over a 3,000-ft (915-m) gross interval. Snider said Tripoint built a special truck outfitted with all the equipment and software needed to assemble the equipment on the rig site within 2 hours of obtaining perforation intervals from the openhole logs. "This Excape method is not suitable for rank wildcats," he said. "Success is a function of knowledge."
Stealing shamelessly
Several technologies from other industries are being incorporated into the Excape system. "Ninety percent of the technology coming into the oil industry was stolen from other industries," Snider said. Time domain reflectometry, a technology used in the communications industry, is being used to measure the length of the perforating wire by measuring the time it takes for an electric pulse to go down the wire and come back up. This can be used to verify that the shots have been detonated at a certain depth even though they cannot be heard so far downhole. Another technology being incorporated is the use of radio frequency identifiers to actuate a specific gun module. This will eliminate the need for hydraulic control line and slotted collars.
"We've got to quit trying to do operations in a well by dunking things down the well - it takes too long to run it and pull it all back up again. Excape really stands for escape from our conventional thought processes," Snider said.

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