Raising an 82,000-tonne iraqi tanker from the ocean floor
- On the afternoon of January 23, 1991, the Amuriyah, an 82,000-tonne Iraqi oil tanker sunk near Bubiyan Island off the coast of Iraq during Operation Desert Storm. In 2014 it was decided the tanker needed to be removed because it was within the tanker turning circle of a proposed mooring point at Iraq’s Al Basrah Oil Terminal, through which 97percent of Iraq’s crude oil is exported.
- To remove the tanker, the 285 metre long hull needed to be cut up into manageable pieces, and it was clear to the general contractor Mammoet, traditional techniques for positioning cutting chains would limit accuracy and lead to deviations in the section weight. In order to control the deviation of the pilots and ensure 100 percent accuracy, the general contractor conducted a worldwide search for technology which would guarantee pinpoint accuracy of the rivercross drilling entry and exit points under the 44.2 metre wide hull.
The pinpoint rivercrossing-drill-hole accuracy of the GyroTracer Directional™ Continuous North Seeking Gyro
- After an extensive international search, Stockholm Precision Tools’ GyroTracer Directional™ Continuous North Seeking Gyro was selected because the North Seeking Gyro proved to be the only tool in the world which through extensive field testing could guarantee the accuracy and speed necessary to complete the complicated rivercross-drilling at the salvage operation.
- Rivercross-drilling is a steerable, trenchless drilling method often used for installing pipes, conduits and cables in a shallow arch along a prescribed bore path using a drill rig, with minimal impact on the surrounding area.
- There were many compelling reasons for Mammoet to select The GyroTracer Directional™ Continuous North Seeking Gyro, but first and foremost it had been extensively field tested and had proven its ability to ensure drillhole accuracy time and time again.
- While most drill contractors rely on drillhole survey instruments to make sure the drill hole is as accurate as possible, recently more contractors are turning to Continuous North Seeking Gyro technology because of its ability to accurately measure angular velocity in real time. The Gyro surveys the wellbore in continuous mode, or real time, at very rapid speed while simultaneously sending data to the operator on the surface, resulting in complete accuracy.
- Unlike traditional survey systems which rely on stationary vibrating technology the Continuous North Seeking Gyro relies on a rotating structure which is 100 times more accurate than the traditional rivercross-drill hole navigation systems. In addition, a North Seeking Gyro doesn’t need to know the starting azimuth or reference point because it is designed to find true north, as opposed to magnetic north, which can shift geographical position over time. The Gyro does this by identifying the earth spin axis from measurements of the angular velocity of the earth’s rotation. Therefore the tool only requires the latitude at which it is being operated. The benefit is each and every individual survey point is measured independently and seeks true north with complete accuracy. And because the North Seeking Gyro is not affected by magnetic interference, it can run inside a casing or in magnetically disturbed ground and provides more reliable data. This proved to be an advantage in raising the Amuriyah as the wreck was highly magnetic.
- Most importantly, the Gyro is guided in real time and surveys the borehole at speeds of up to 150m/min while simultaneously sending data to the operator on surface. This also contributes to the accuracy of both horizontal and vertical well profiles and helps to ensure there is no degradation in the drill-hole accuracy.
- The general contractor is internationally recognized for environmental stewardship, and in keeping with this highly regarded principle it was a priority that all the Rivercross drilling would have a minimal impact on the marine environment. Given the accuracy of the GryroTracer Directional™ in Rivercross Drilling and the ability to work in real time, there was a single an entry and exit point with no other significant impact of the surrounding environment. Most importantly, the drill holes are precise so only drilled once, with minimal disturbance --especially important in sensitive and bio-diverse environments.
- The GyroTracer Directional™ was attached to a modified horizontal directional drilling rig, placed on a tailor-made stirnger beam and fitted alongside a barge. The stringer was then submerged at an angle of 22.5 degrees until its front reached its exact designated positions on the ocean floor. At this point the drilling began.
Successful salvage operation results in new civil applications for GyroTracer Directional™ Continuous North Seeking Gyro
- This successful salvage operation was the first time a GyroTracer Directional™ Continuous North Seeking Gyro was used in Rivercross-drilling and the accuracy proved to be unmatched by any other navigational tool; other tools are less accurate and could not work within the 1 metre margin of error the project required. With the accuracy provided by the GyroTracer Directional™, nine rivercrossing drill holes were completed and once the drill bit resurfaced precisely where it had been intended, the cutting chains were run through the pilot holes. When the chains were in place, the oil tanker was then cut into sections. GyroTracer Directional™ Continuous North Seeking Gyro was the only way to accurately run the cutting chains under the 44.2 metre hull of the tanker. Any other method would have been too imprecise.
- The job was done with absolute precision and in record time. Both the general contractor and the local city council expressed their appreciation to Stockholm Precision Tools, because without the Amuriyah’s expedient removal, the construction Al Basrah Oil Terminal would have been cancelled.
- What is even more apparent to the industry was the potential applications of the GyroTracer Directional™ Continuous North Seeking Gyro in rivercross drilling. This project demonstrated the accuracy of the technology in rivercross drilling and the potential application for other industries, such as installing pipes, cables or conduits over long distances with speed, accuracy and precision. The superior accuracy of the directional north seeking gyro is also now backed up by field comparisons data and field operator experience.