Downhole disintegration

A new concept in well tools could see one-off tools built, run and left downhole to disintegrate. Elaine Maslin reports.

A computer graphic of the FLI design. Images from Well-Sense

Disintegrating downhole tools have been making an impact on the US-onshore business, starting with disintegrating frac balls and more recently completion tools, such as frac plugs and bridge plugs.

The technology follows a trend observed in plastics and in metal in the medical space where implants could be designed to dissolve. The idea is that materials, from plastic bags to high strength metals, on contact with a fluid, such as brine/acid and heat, can dissolve, disintegrate or corrode such that they’re not going to cause an impedance in the wellbore, rubbish dump or even the human body.

In the medical space, the concept is being developed using magnesium and iron that is 3D printed into parts, which can be used as scaffold for healing bones, in place of screws, pins, rods or plates currently used.

A newly launched UK-based oil services firm, Well-Sense, is looking to use this technology into the well intervention space, alongside fiber optics, to create a new discipline, says its founder Dan Purkis.

The ex-Petroleum Engineering Services and Petrowell inventor’s method is called FiberLine Intervention, or FLI, involving a gravity deployed tool which spools out fiber optic cable, linked to surface for real-time data transmission, including video, like some wire-guided technologies outside the industry. Once it has done its job, the tool will disintegrate downhole.

The benefit of a tool that disintegrates downhole is you no longer need topside intervention equipment, such as a coiled tubing, wireline or electric line unit, making it suitable for use on installations with no free deck space or structures that are unable to take extra weight. Components within the tool can also be “off the shelf,” as the tool no longer need to withstand long periods of exposure to downhole conditions or be required to be used again.

Dan Purkis

“If you don’t have to take the tool out you don’t need anything at the surface,” Purkis says. “Leaving tools downhole is seen as a problem. But if it dissolves you could leave it in the well.” With a fiber connection to surface, raw data can be transmitted, with no processing required on the tool, minimizing what is required on the tool and meaning very little power is needed.

“All we need is the sensor itself, i.e. a camera or casing collar locator, straight to the optical transmitter,” Purkis says. “You could have eight cameras on the tool, two looking down and six on the sides, running on a small battery.”

The technology will use magnesium and other light metals, which disintegrate when exposed to certain environments, such as liquids or heat, due to transfer of ions from the magnesium breaking it down. Well-Sense is looking at using magnesium and aluminum.

The “off the shelf” components inside the tool will be protected using a heat shield for as long as they need to be – around 30 minutes to an hour – to let the tool do its job and send the information required to the surface. The heat shield the firm is looking to use will be based on a sacrificial material, a phase change material, which remains a certain temperature as the temperature increases, it erodes as it absorbs the heat energy, like ice in water.

Using fiber means being able to draw on recent distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) technologies, which let you monitor along the full length of the fiber. This could be used to detect leaks or assess sand production down the length of the wellbore and also range-find the device down the wellbore. This would also be cheaper than permanent fiber installation, but also fiber deployed on carbon fiber rods, or fiber in wire, Purkis says.

In fact, DAS work looks set to be the first trial of Well-Sense’s technology, with an operator probably in Houston or maybe Alaska, sometime this year, Purkis says.

Of course, there are limitations. Being gravity deployed, there will be wells with an angle at which it will not be suitable – Purkis is developing a new type of tractor to overcome this. And there are some things that won’t dissolve – the electronics and the batteries. But, these will leave just small amounts of debris, Purkis says.

He says anything that runs on electric line could be configured to run using this method. And he has plenty of other ideas for its use, such as helping to determine with greater accuracy where wells actually are, which would help plan wells areas where they have been drilled in high density and there’s a risk infill wells could connect with older wells. This would be by using an inertial navigation system – which could be bought for $200 off the shelf and is as big as your thumb, Purkis says.

As another example, he suggests using explosives in the tool for well re-perforation. “It’s not a tool, it’s a new discipline,” Purkis says. “We want people to develop their own tools to go on this method.”

The technology has been assessed by the Aberdeen-based Oil & Gas Innovation Centre, which then put out a call for expressions of interest to the academic and research community, resulting in Robert Gordon University, Aberdeen, being selected to work with the company on developing the concept.