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BP sets new record for coiled tubing Milne Point sidetrack well extends out to a measured depth of 22,461 feet, beating the previous record of 20,540 feet set in 2005 Alan Bailey Petroleum News
On Feb. 25, after 19 days of drilling, a coiled tubing sidetrack from the MPL-36 well in the BP-operated Milne Point field on Alaska’s North Slope reached a measured depth of 22,462 feet. BP thinks this is a world record for a coiled tubing well, Sean McLaughlin, BP coiled tubing drilling engineer, told Petroleum News March 9. BP set the previous record depth of 20,540 feet in the Niakuk field in 2005, said BP spokesman Steve Rinehart.
Nordic Calista’s rig 2 drilled the record-breaking Milne Point sidetrack, hitting a field reservoir target 6,650 feet below the surface at a horizontal distance of 19,569 feet from the wellhead. BP thinks that the well’s horizontal departure also sets a record for coiled tubing drilling.
The MPL-36 well required a huge 25,000-foot reel of coiled tubing, manufactured in Houston, Texas, and transported to the North Slope via the Alaska port of Whittier. The reel was fitted on a special trailer, so that the railroad car carrying it would fit through the rail tunnel at Whittier, for rail transportation to Fairbanks, and hence by truck to Prudhoe Bay, Rinehart commented.
Continuous tubing The coiled tubing technique involves drilling with a continuous length of narrow-diameter and relatively flexible steel tubing, rather than the rigid, 30-foot lengths of drill pipe used in a conventional drilling operation. And, as in the MPL-36 well, a typical coiled tubing operation involves extending the use of an existing well by punching a hole in the side of the well bore; feeding the coiled tubing down the well and out through the hole; and then drilling out from the old well.
In the case of MPL-36, the original well was no longer productive but BP wanted to use the well to access a new section of the Milne Point oil reservoir some distance from the wellhead without having to construct a new gravel well pad, McLaughlin explained.
“We’re not making any more pads and so we drill all our wells from (existing) gravel pads with a tight well spacing and we have to drill out underground a considerable distance to access the reserves,” McLaughlin said.
In addition, in the MPL-36 drilling operation BP wanted to test the practicalities of drilling out over very long distances, as a prelude to perhaps developing some other opportunities in oil pools far from a well pad.
Because the drill pipe is fed into the well from a coil of tubing on a large spool mounted on the drilling rig, it is impossible to rotate the drill pipe in the well, to turn the drill bit and thus augur the tubing through the subsurface rocks. Instead, a motor attached to the far end of the coiled tubing turns the drill bit, with the fluid mud that the drillers continuously pump through the well powering the motor. A device at the surface pushes the tubing into the well, to help drive the bit through the rocks.
Electric line An electric line passing though entire length of 2 3/8-inch-diameter coiled tubing in the MPL-36 well allowed the drilling crew to communicate with equipment located just above the drill bit, enabling the crew to steer the bit precisely along a planned drilling trajectory while also enabling the continuous collection of data about the rocks that the drill bit encounters.
A conventional drilling operation generally uses a system of pressure pulses transmitted through the drilling mud to communicate with downhole drilling tools, but this mud pulsing technique becomes problematic through 25,000 feet of coiled tubing, McLaughlin explained.
In addition, the electrical system enables the necessary level of directional control for the coiled-tubing drill bit, he said.
To prevent the collapse of the new sidetrack wellbore for the MPL-36 well, especially in the notoriously unstable shale horizons at Milne Point, the drillers used a technique known as “managed pressure drilling” in which the drillers maintain from the surface the pressure of the drilling fluid in the well in situations where the tubing has to be extracted from the well.
Particular challenges The drilling in the MPL-36 well presented some particular challenges because the original well is inclined at about 80 degrees from the vertical, extending for more than 17,000 feet at this shallow angle. Teasing the flexible tubing down such a shallowly inclined well bore to a considerable distance before executing the sidetrack is especially difficult, and removing well cuttings up a very long incline also becomes problematic.
“Exactly what makes this well challenging is not just the major depth, it’s the horizontal departure that we have,” McLaughlin said.
But, with coiled tubing drilling being relatively new, nobody really knows how far it might ultimately be possible to drill using the technique, he said.
“We really pioneered the service in the early ’90s up on the North Slope and we are still expanding our knowledge of what we can do,” McLaughlin said. “… This (record-breaking well) isn’t the technical limit. This is a step for us. There are probably some big wins out there yet to come.”
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