The Texas A&M University team’s 8-ft maroon-colored drilling machine started lowering its bit to the surface of the test rock.
Guided by load, rotation, and vibration sensors, the drawworks inched the topdrive downward in a series of short thrusts before the bit touched the bottom. With the bit in place, a single button push was all it took for the device to begin drilling, after which it required no human guidance.
A&M was one of the four finalists in the SPE Drilling Systems Automation Technical Section’s (DSATS) first Drillbotics competition. The two-phase contest required teams of university students to submit plans for automated drills in the fall. Four finalist teams were selected to build machines and test them before judges on their respective campuses in the spring.
After an hour-and-a-half of drilling, the power tool buzzing that observers had grown used to hearing began to sound like a jackhammer. “What was that?” one of the competition organizers, Fred Florence, asked the A&M students over the loud rattling.
The team members reacted stoically by watching the output of their computer screen more closely, but never looking upset. They had stayed up all night in preparation and contest rules prevented them from making any manual corrections beyond the work already completed over the past year.
Water began leaking from various points on the drillstring. The bit had reached the 2-in. layer of granite sandwiched between the 1-ft-thick sandstone blocks. Minutes later, the drillpipe twisted off just below the topdrive and the emergency shutdown was engaged.
The granite layer, which also broke the other three teams’ rigs, was added to the sandstone blocks to test the ability of rigs to adapt to sudden changes in environment without manual guidance.
Weight on bit and rotational speed had to be automatically increased or decreased by the teams’ algorithms to maintain a good rate of penetration in drilling through the hard layer. “There’s damage that can occur with constant rotation and constant weight on bit,” said Florence. “In certain situations, the bottomhole assembly can become very unstable. But you can make it stable again by increasing or decreasing the weight on bit or rotation speed.”
Designing an automatic drilling system that is able to perform dynamic adjustments required more than just petroleum engineering expertise. A&M’s team of graduate students was led by Narendra Vishnumolakala, who has a background in instrumentation and electrical engineering and is pursuing a master’s degree in petroleum engineering. His teammates were Prudhvi Maddineni, an electrical and computer engineering student; Seounghyun Rho, a petroleum engineering student with experience in civil engineering; and John Kim, a petroleum engineering student.
With its knowledge on a wide variety of subjects, the team was able to save money by building some sensors themselves, such as the optical tachometer, which measured the rotational speed of the drillstring. The contest rules allowed teams to spend as much as USD 15,000, but the team built their rig for approximately USD 12,000.
While all teams produced functioning rigs, none of them was able to drill all the way through the granite. Judges expected rig problems with this layer, according to Florence. A&M’s rig was able to drill roughly halfway through.
Another obstacle that students had to overcome was working with a thin drillpipe of ⅜-in. diameter with a 0.016-in.-thick wall. In his pretest presentation, Vishnumolakala said that his team members assumed that they would be given a sturdier pipe by DSATS. This weak link forced them to rethink their strategy after the rig was constructed.
“Based on the test results, we made changes to the design and program,” he said. “After a few tests (and breaking a few pipes), we finally arrived at an optimal combination of parameters to operate, which we used on the final test day.”
During the competition, when the rig reached the granite layer, the team’s drilling algorithm decreased the amount of weight on its bit and increased the rotational speed to compensate for the adjustment. More weight would have been helpful, but due to the drillpipe’s weakness, A&M’s team prevented its algorithm from applying more than 50 lb of weight.
Unfortunately, the increased drilling speed caused a destructive resonance in the drillstring. “The large lateral vibrations led to fatigue failures of the pipe, first noticed by the students when the pipe parted just below their topdrive,” said Florence. “When we heard the unusual noise, we suspected a twistoff at the bottom of the string, but because the tube was constrained in the tool joints we built, it was not obvious to the students.”
From Vishnumolakala’s perspective, the pipe failed because of inaccurate vibrational data from the accelerometer. The team could not attach the sensor directly to the drillpipe, which resulted in incorrect readings.
However, in order to win the competition, teams were not expected to build perfect rigs. The scoring rubric made it clear with the “Lessons Learned” category that figured into the judges’ overall scores. “Remember: The drillpipe failed, you didn’t,” said Florence while addressing the A&M students after all motors were quiet and judges were reviewing the aftermath.
The University of Oklahoma team won first place because its rig performed slightly better than the others, and its control model showed a better knowledge of the drilling issues it faced, the judges said. They also pressurized the drillpipe to stiffen the string against pipe buckling.
The competition will become tougher as DSATS introduces new challenges, such as directional drilling and the use of drillstring sensors. “Next year, the formations will not be parallel, and the dip will make it challenging to drill a vertical well,” said Florence. Rig designs can be resubmitted in future competitions so that future contestants will benefit from the lessons learned by past teams.
Florence hopes these competitions will one day result in technological breakthroughs in the field of drilling automation. “I want these students to teach us new and innovative ways to drill,” he said.
The University of Oklahoma team will present a paper outlining its efforts during the 2015 SPE Annual Technical Conference and Exhibition on 28–30 September in Houston. The other teams will give their presentations at the DSATS symposium on the day before the conference.