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The brains behind the bit

A self-adjusting drillbit began as a clever concept in a company-wide innovation contest. Now its backers say the adaptive “smart” bit could become an industry standard.

A new adaptive PDC drillbit from Baker Hughes can adjust the depth of cut without intervention from the surface.

The technology introduces a moving element to the standard PDC drillbit. The TerrAdapt PDC bit responds to reservoir and drilling conditions in real time to mitigate stick-slip issues downhole and resist sudden changes in loading.

Danielle Fuselier, product line manager for diamond bits, says the service company put “intelligence into the bit to enhance drilling efficiency”.

Stick-slip is a torsional drilling dysfunction that can cause the drill string and the bit to accelerate and decelerate quickly.

In severe cases, the drillbit can get stuck while the string continues to twist and wrap, leading to a violent release of energy that can damage the bit and drill string tools.

However, stick-slip situations are not easy to prove unless in-bit sensing or measuring while drilling (MWD) technology is used during drilling.

Most wells are drilled with limited vibration measurement technology, Fuselier says.

“We fully believe stick-slip is a much more common dysfunction than we’ve measured to date, especially with the increase in higher strength, higher torque motors. The loading put on bits has continued to increase, and coupled with varying rock strength leads to a stick-slip-rich environment.”

TerrAdapt Photo: Baker Hughes

TerrAdapt TEST DRIVE: Baker Hughes’ new TerrAdapt bit before testing at the BETA facility in Oklahoma (top), and after a run. Photo: Baker Hughes

Traditionally, engineers have used two main methods to prevent stick-slip. The first relies on bit design and setting a precise depth of cut for the entire drilling run.

The trade-off is the bit may not be as effective as the formation changes along the wellbore.

“The industry uses a fixed amount of depth of cut control and you are stuck with that the entire well. If you set the limit too high, you can drastically reduce your ROP (rate of penetration). If you set it too low, it may do nothing to prevent stick-slip,” Fuselier says. “Its a constant educated guessing game.”

A second method for mitigating stick-slip adjusts the weight on bit or the rotations per minute (RPM).

“If stick-slip is suspected, the driller will usually decrease the amount of weight applied to the bit or rotate the string faster. This can cause the bit to go into a different kind of vibration – which is also very damaging.

"The other challenge with this method is it is very hard to know what exactly is happening at the bit, and it takes time to understand if the changes solved the issue, or caused something else to occur,” she says.

Changing behaviour

The new bit, TerrAdapt, works by adjusting in real-time the depth of cut control in response to the drilling conditions.

“Before TerrAdapt, you had to have a very precise and singular depth of cut setting for the entire well. We have a range now,” Fuselier says.

“If the bit is experiencing stick-slip, the depth of cut control elements adapt to mitigate that dysfunction. If a slightly harder formation is encountered, you are not stuck with one amount of engagement.

"If slightly softer rock is encountered, the elements will recess to maximise ROP, provided there are no torsional vibrations.”

The depth of cut elements, contained in cartridges installed in the PDC bit blades, can extend in milliseconds and fully retract in tens of seconds, depending on how far they extend. Once smooth drilling resumes, the TerrAdapt elements retract back into the cartridge to maximise the bit’s full ROP potential.

TerrAdapt3.jpg Photo: Baker Hughes

TerrAdapt REACTION: The TerrAdapt bit can respond in real-time to reservoir conditions to mitigate stick-slip issues Photo: Baker Hughes

One of the biggest draws of the automatic adaptive technology is that engineers on the surface cannot “really know what’s going on 10,000 feet downhole”, Fuselier says.

“It responds in real time. It doesn’t have to wait for the surface to realise there’s an issue, and the driller doesn’t have to do any guesswork.”

Each cartridge is sealed off from the mud system, and each moves independently. Part of the technology development focused on ensuring installing cartridges in the bit blade will not compromise blade integrity. The service company engineered a retention ring to lock the cartridges into place.

“If something were to break down it would not cause the bit to be tripped out immediately. Either the depth of cut control element would be fully recessed, which is the same as any traditional bit with no depth of cut control, or it would stop working fully extended, which is the same as today’s fixed depth of cut control bit," Fuselier says.

"The drilling behaviour may not be ideal but it would not cause drilling to be stopped.”

The cartridges contain hydraulic oil and a piston assembly that moves up and down to control the depth of cut control. The cartridges are also designed to withstand the duty cycle of multiple runs.

Innovation origins

The idea for the TerrAdapt bit emerged during Baker Hughes’ Wildcat Challenge, a company-wide innovation contest launched in 2013.

The team behind the self-adjusting PDC bit, one of four winning ideas, proved the concept in 2014. Formal commercial development began the following year.

The team tested the design at the Baker Hughes Experimental Testing Area in Oklahoma. Fuselier says that during those tests the team drilled more than 15 intervals across six wells with the TerrAdapt bit versus a standard PDC bit, with varying bottomhole assembly designs.

Most testing was in vertical and the curve-to-lateral sections of a wellbore, but Fuselier says slim horizontals is a direction the team wants to head in.

“We drilled in parameters we knew instigated stick-slip dysfunctions, but we didn’t have the stick-slip with TerrAdapt,” she says.

“We tried to force the bit to go into stick-slip, but the TerrAdapt mitigated the dysfunction, whereas a standard PDC bit without depth of cut control would go into stick-slip pretty easily.”

TerrAdapt DAMAGED GOODS: The effect of stick-slip is visible on a conventional bit. Photo: Baker Hughes

Baker Hughes lined up customers that reported torsional vibration issues and were willing to try out the new adaptive bit.

Field trials began summer 2016. The field trials all used in-bit sensing to measure how much stick-slip was happening.

Full commercialisation is scheduled for this month’s IADC Drilling Conference in The Hague.

The TerrAdapt bit is available as a customisation on the service company’s line of fixed-blade bits. It will be available in a range of sizes, from 8 3/8 inches to 12 1/4 inches, which Fuselier says will meet the majority of domestic drilling and a lot of international drilling needs.

The bit technology can be used with different numbers of blades and cutters. Under current design practices, she says, three cartridges are most common but bits with four blades and four cartridges would be available.

Fuselier sees a future where the self-adjusting bit is a standard choice, not just selected in situations where stick-slip may be an issue.

“What else can we move on a PDC bit to improve drilling performance?” she asks. “Our future development efforts will be geared towards expanding our smart bit platform.”

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