June 2016 /// Vol 237 No. 6

Columns

What's new in production

Perforating, perforce

Don Francis, Contributing Editor

An interesting blip appeared on the radar screen recently—a perforating system that operates without explosive charges.

For completing multi-stage wells, sliding-sleeve technology may be getting a lot of attention these days, but plug-and-perf (PnP) remains Old Reliable for many operators. The argument generally goes something like this: PnP is cheaper and faster than sliding sleeves, which require special surface setup to release balls. Sliding sleeves are more complicated and expensive, and take more time to deploy.

Maybe. In the interest of fair and balanced reporting (no underbalanced reporting here), a counter-argument recently made by Michael Mayer, in an industry discussion forum, sums things up. “Plug-and-perf is definitely not faster and arguably not cheaper. The added cost comes from the initial purchase of the sleeve system. A 32-stage well utilizing ball and sleeve can be completed in four days, where the same well would take up to two weeks using plug-and-perf. Minimal additional equipment is required (extra frac pump and a few extra pieces of iron). Plug-and-perf has the added cost of having wireline and a frac fleet on location for two weeks. The use of dissolvable balls reduces the need for a clean out after completing the well. The same thing can be achieved with plug-and-perf through the use of dissolvable plugs.”

Mayer goes on. “As for closing sliding sleeves after the well is on production, the vast majority of sleeve systems used do not have this capability. They are shifted by sheering sheer pins so once they are open, they are open. If there was a good system for opening and closing sleeves, re-fracs would be much more common.”

The debate won’t get decided here, but if you’re in the PnP camp, then you may wish to Google the Gator (who names these things?) perforating system. According to its developer, the system uses a proprietary, hydro-mechanical design to perforate casing, with an increase in safety compared to conventional explosive perforating tools. The design enables repeat use, and it’s claimed that the system can perform unlimited perforations in a single trip.

But here, safety is the big deal. Because it eliminates explosives, the system can be used in highly populated or high-traffic areas.

Meanwhile, one interesting development has nothing to do with how the perfs are actually made. Schlumberger has introduced a dissolvable PnP system that uses degradable fracturing balls and seats instead of plugs to isolate zones during stimulation. The company says the system is suitable for cemented, uncemented, vertical, deviated, or horizontal applications in shale, sandstone, dolomite and other lithologies. This development is not directly about personnel safety; it’s the removal of economic risks associated with mechanical intervention. The company points out that in depleted reservoirs, it is difficult to manage the removal of milling debris, increasing costs and the risks of getting stuck. Rigging mechanical intervention equipment up and down carries its own risks.

But back to safety. Needless to say, the Big Risk involving personnel safety in explosive perforating is inadvertent discharge. This can happen if enough voltage at the proper polarity is misapplied to the wireline. This misapplied voltage could be from a number of sources, including stray (cathodic protection, leaking electric cables on rigs, etc.), radio frequency (RF) or human error.

Albert, et al (2015) state, “It has been proven that radio frequency (RF) transmitted signals can initiate detonation of an electrical blasting cap; therefore, RF-safe procedures must be in place when performing electrical wireline perforating. To maintain RF safety, standard electrical detonators require an RF-free perimeter be maintained…Decades ago, an RF-free well site was not difficult to achieve, but with the proliferation of cell phones, GPS devices, radios, etc., and the large operational footprint for multi-stage completions requiring continuous communication to properly coordinate, it has become very difficult and expensive to maintain an RF-free zone around the perforating operation. Over the past two decades, several RF-safe ballistic initiating devices were introduced…but some of these RF-safe systems were complex, thus adding significant costs, or reducing reliability.”

But ingenuity rides to the rescue, in the form of addressable switches, a new method for controlling voltage directed to individual perforating guns. “This new select-fire perforating method replaces pressure switches with smart switches that include intelligent electronic circuits with unique digital addresses that can be addressed through simple telemetry systems. The new system includes a surface panel that can communicate with each of the downhole circuits. Through the surface panel, the wireline operator can identify each of the gun modules, determine their status, and then control the circuits to direct voltage to a detonator connected to the digital switch.

The authors say the advantages are persuasive. Among them:

  • Addressable switches can block all sources of inadvertent current from the electrical detonators in the tool string.
  • The switches, when integrated with standard detonators, are certified RF safe.
  • Real-time shot detection provides immediate feedback on whether plugs have set or guns have fired.
  • Individual gun sections can now be skipped if any section fails to detonate.

Here’s a fun fact about reliability, as offered by the authors: The probability of getting a hole-in-one: 1 in 12,000. The probability of unintended initiation of an addressable switch detonator: 1 in 72,000,000,000,000,000. That’s a pretty good argument. wo-box_blue.gif

The Authors ///

Don Francis DON@TECHNICOMM.COM / For more than 30 years, Don Francis has observed the global oil and gas industry as a writer, editor and consultant to companies marketing upstream technologies.

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