Posted onAugust 9, 2017
Until Now, Innovation = Less of the Same
AUTHOR: MATTHEW CRUMP
In the beginning
In my previous article I highlighted the fact that operators are drilling longer laterals and breaking those lateral up into even more stages. The result is a new need for a completion solution that reduces risk, reduces debris in the well, and the time it takes to remove it. To understand the current completion technology used for multistage fracing you have to go all the way back to the beginnings of the oilfield services industry.
Over 70 years ago, RC Baker filed a patent for a Hydraulically Set Well Packer. This is the first reference to a packer designed to anchor in the well, provide a seal, and remain autonomously downhole. The distinctive piece of innovation in this patent is the upper slip, rubber element, lower slip configuration that locks the packer in the well and keeps the seal energized. Clearly this has proven to be a hugely successful design considering it is the basis for almost all packer products available today.
As the industry matured both in applications and technology there arose a need for a similar packer that could be easily removed from the well after it had served its purpose. This led to the development of the cast iron bridge plug. In 1963 D.L. Fry was awarded the patent for a cast iron bridge plug. This is very similar to the original RC Baker patent, however it was constructed from cast iron making it easily removed from the well.
As material science became better known and the industry continued to innovate, there came the option to modify this assembly for even easier removal through milling. And this was the introduction of composite packers.
In 1993, Steven Streich et. al. was awarded a patent for a downhole tool with non-metallic components. This technology contained much less metal content and was designed to mill up even easier. Though, as you can see, its largely unchanged in form from the original RC Baker Patent from 1947. Another interesting note is that this technology was developed long before plug and perf became the dominant form of completion and yet the clear majority of plugs run today look exactly like this plug.
Finally, taking it one step further with material technology a fully dissolvable plug was developed, maintaining the same form.
The Common Thread
If you look at the common theme between these technologies it is really the slip-rubber element-slip configuration that is designed to create the anchor and seal. Over a 70+ year period this configuration has remained the same. Why? It is a very effective method to achieve the anchor/seal goal, it is easy to scale up and down, and it’s comfortable. It’s just the way we’ve always done it.
The Application Has Changed
The issue with the slip element slip configuration is that the demands placed on most packers run today are much different than the original application. The application of running a production packer involves running one packer in each well, lowering it slowly into the vertical section, it’s constructed largely from metal, it’s goal is to hold pressure from above and below, and it remains permanently in the well.
During the plug and perf completion operation we are regularly pumping 50-100 plugs (or packers) into the horizontal section of the well, they’re made largely out of composite material, they only see pressure from above, and then they’re milled out.
The application today is completely different than what RC Baker was designing for. The three phases of a composite plug’s operation are pump down, set & hold, and mill up. The slip element slip creates issues during all three phases. During the pump down operation the plugs are pumped through the casing at high velocity (up to 800 ft/min) with high pump rates (up to 20 bbl/min) with just a ¼” of clearance on each side of the plug. The tight clearances and flow rates around the plug create pressure drops that can cause the rubber element to swab or swell. This swelling increases the OD of the plug and increases the chances of snagging up in the well. Also, with having two sets of slips there is more opportunity to get caught on something in the well and presetting.
During the set and hold, the element is compressed and kept compressed with the slips. Compressing the element creates a force against the mandrel of the plug. Once the pressure is applied, it adds further to the amount of force against the mandrel. With most plugs rated at 10,000 psi, the amount of force on the mandrel is huge. This requires the mandrels to be thick so that they’re strong enough to handle these forces.
To bring value during mill up the goal is the reduce the overall material in the plug as well as the amount of hardened material. Again, with two sets of slips you have double the hardened material. Also, the thick mandrel that is required to handle the forces exerted on it from the rubber compression and frac brings more material that must be removed.
It’s clear that the slip-rubber element-slip configuration is effective at creating an anchor and seal, but misses the mark for the other demands of the plug and perf application.
Until Now, Innovation = Less of the Same
Since the beginning of the shale revolution the major plug and perf completion technology has remained largely unchanged. While the major service companies have recognized the need to provide composite plugs with less material and less metal the fundamental design of their products has endured. They have found ways to shorten their plugs or to swap out composite for metal on some of the components, however the results have been incremental in nature. Even smaller composite plug companies that have made a significant impact on the industry have just followed the same equation. The industry needs the next step in composite technology that isn’t hand cuffed by the legacy of previous designs.
The Choice is Clear
The Rubicon RzrFRACTM provides the next step in composite technology reducing risk, providing a competent anchor and seal, and significantly reducing the amount of debris from the well. If you’d like to know more about the RzrFRACTM and how it can help you reach your completions goals. Please contact me at firstname.lastname@example.org or come see us at the DUG Eagle Ford Conference August 29-31, 2017 in San Antonio, TX.