In drilling oil and gas wells, a similar problem arises. Unless coiled tubing is used, heavy joints of steel drillpipe are screwed together sequentially as drilling proceeds. When a new joint of pipe is added, its narrow end is screwed into the open end of the old joint in a process that’s repeated as the well deepens. But the over-tightening doesn’t arise here.
Well operators are usually under pressure to drill quickly. While onshore costs pale beside those incurred in the offshore, the former are easily high enough to discourage any laxity in the pace of drilling. Pressure is also put on drilling contractors, who are expected to drill quickly to total depth and cut overall well costs.
For drillers, more weight-on-bit usually means faster drilling, while increasing torque – a force akin to that in a twisted elastic band – often achieves the same result. As with wheel nuts, though, there’s a happy medium for torque, beyond which over-tightening of threads can inflict damage to drillpipe.
The damage that over-torquing does to drillpipe is far more costly than a few nuts and bolts, however. The pipe must be re-machined and re-threaded. According to Steve Collier, chief operating officer of Rigworks Oilfield Solutions Inc., few studies have addressed just what torque-induced damage costs the oil industry each year, but anecdotal evidence suggests it’s plenty.
“You can quantify [the damage] by the fact that there are at least 15 shops [in Nisku, Alberta] that repair threads on damaged pipe,” he says. “About 90 per cent of the time, that damage is due to over-torquing.”
Apart from being the base for some drilling contractors, the industrial suburb of Nisku is home to Rigworks, which rolled out its own instrument to measure torque on the drillstring about four years ago. The Sentry Torque System was designed to help drillers make optimum use of torque and avoid the drillpipe damage that keeps Nisku’s machine shops hopping.
Other methods of gauging torque on rigs rely on hydraulics, but the Sentry sensor is electronic, giving the driller a digital readout of torque on an electronic display. Hydraulic sensors, Collier says, only render an indication of torque, while his system provides a truer, more accurate measure.
For the industry’s more experienced drillers, Collier concedes the Sentry may be of less use, since old hands can often sense when torque, among other parameters, is being pushed too high. But the Sentry will allow less experienced drillers to achieve maximum rate-of-penetration (ROP) without damaging the drillpipe through excessive torque.
“That’s where our torque system comes into play,” he says. “We all know what will happen over the next 21 months, with [drilling] personnel and rigs. We’re going to have more inexperienced drillers coming up the ranks, while the more experienced ones are retiring.”
The Sentry system will work with most automatic drilling systems, allowing drillers to pre-set parameters so that, if a certain level of torque is reached, the system will automatically take weight off bit. “It will still give you maximum optimization and weight-on-bit, but it will reduce the amount of torque on the pipe, allowing for a more consistent ROP,” he says.
Designed strictly for rotary drilling rigs, the current Sentry system includes software that lets the operator look back and check the well’s history, viewing the points when torque or weight-on-bit peaked. That feature, Collier says, could be important for contract drillers, especially when it comes to sorting out who foots the bill for torque-induced damage to drillpipe.
Under many contracts, the well operator is liable for such damage, but that’s not always the case. Much depends on the contract between drilling contractor and operator, and liability for damage may also depend on other factors, such as the operator’s instructions to the driller, according to Collier.
In the past, the question of who was responsible for damaged drillpipe was often a grey area, and those involved usually had no way to prove it. “Today, upon hole completion, they can go back through the drilling program and say, ‘Well, we spiked here, but the engineer said move forward and that’s when we damaged the pipe,'” says Collier.
The man who developed the Sentry system, Brady Marshall, is Rigworks’ founder and president. A heavy duty mechanic by trade, Marshall worked on drilling rigs worldwide, having developed and built oilfield equipment over the years. While the core of the torque sensor was designed and made by a German company, Rigworks developed the Sentry system for rotary drilling rigs, and a patent is pending.
Although new to most people, the Sentry Torque System has been undergoing field-testing in Western Canada for more than three years. In that time, at least two drilling contractors, Calgary-based Ironhand Drilling Inc. and Red Dog Drilling Inc., have used the system. The Sentry unit, which resembles a rotary bench grinder, has been working on Red Dog’s rig number two since February 2007.
“It basically saves the life of our drillpipe,” says Wayne Zandee, president of Red Dog, based in Estevan, Saskatchewan. “I don’t have to replace the drillstring as often.”
When Red Dog’s drillpipe suffers thread damage while drilling, the well operator pays the freight. Nevertheless, the Sentry has been worthwhile, Zandee says. “Every time you have to repair [drillpipe] threads, you lose a bit of life out of that drillpipe. Eventually, I’ve got to replace the pipe, and it gets costly,” he says.
Apart from shortening the life of drillpipe, Zandee says repairing thread damage means losing a few inches with each repair. “A tool-joint is eight inches long, and if you take a few inches out of it every time, you’ve got to throw it away, because [eventually] you don’t have a tool joint left.”
Zandee did not monitor what Red Dog spent each year on torque-induced thread damage before installing the Sentry, or what the company has since spent, for comparison purposes. Yet, quantifiable or not, he is satisfied he has seen savings.
“It’s going to have to be stretched out over five or six years for me to see the savings in the cost of putting the rotary torque sensor in, but I believe [the savings] are there. I haven’t put it on the other rigs yet, but I’m looking at putting it on our rig three,” he adds.
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