May 2009 Vol. 236 No. 5

Features

Challenging HDD Project Provides 10,000-Foot Record-Setting Crossing

A new global horizontal directional drill (HDD) undersea crossing record has been set in terms of pipe diameter, pipe weight and length of crossing in Saudi Arabia.

The record-setting bore came during the drilling of a second 10,000-foot bore and pull-in of a 30-inch pipe near Al Jabayl for the Berri Causeway Pipeline project. This second bore was 42 inches in diameter and qualifies as a new world record length crossing.

In 2007, Tatco Boring of Abu Dhabi was awarded the Berri Causeway Flank 2 HDD project. The main contractor is Al Robaya Est. and the owner is Saudi Aramco. The project required a bay crossing comprising two parallel pipelines, each more than 3,150 meters in length. The first was a 24-inch oil trunkline that required a 32-inch bore. The second involved a parallel 30-inch steel water line that weighed in excess of 1,525 tons and required a 42-inch bore.

Shortly after completing the 24-inch bore, the contractor was made well aware that a new approach was needed. This led to Transcontinental Supplies Inc., (Transco) of Weatherford, TX – an HDD drilling tool, engineering and custom manufacturing firm – becoming involved in the planning phase for the 42-inch bore.

From information gathered during the drilling of the first crossing, it was known that the soil formation at the crossing was soft sandy limestone with several sections of medium to medium-hard calcarenite.

Fluctuating Bit Needs

During the drilling of the first crossing, cutter pick type bits were effective in the very soft sections but failed in the harder sections, resulting in numerous trips. In the harder sections, the roller cutter hole opener was able to drill effectively but would ball up and quit drilling in the softer sections. Therefore, multiple trips had to be made on each enlarging pass to change bits, which had the potential to cause drilling and safety problems.

To overcome these challenges, Transco designed a product capable of drilling both formations effectively. Since the harder sections required rolling cutters, a steel tooth bit type was selected as the design platform to efficiently drill the harder formations. The teeth were also long and widely spaced to keep the cutters from balling in the soft ground. Also, a long-life bearing seal combination was required so the bit could last while drilling over the entire section.

Moreover, a maximum pull force was established to prevent tooth breakage in the calcarenite and a controlled rate of penetration was selected to help to prevent balling. In addition, the drilling tool was designed to rotate at 28 rpm at all times and in all formations.

It was also established that the primary rig with a 250-ton unit on the pipe side to assist rotation, had sufficient pull, torque, pumps and drill string to attempt to go from the 12 1/4-inch pilot to a full 42-inch bore in a single pass.

The final design featured a hole opener with a 28-inch three-cutter first stage followed by a 42-inch cutter second stage with a barrel-style body to maximize stabilization and lower torque.

A barrel-type hole opener body was also chosen to minimize torque overall and prevent “grabbing” on faulty rock in the hard sections. It was also less likely to sink in the very soft sections during stationary rotation for mud mixing and conditioning. Two stages of cutters were necessary to span the 15-inch kerf. Milled teeth cutters were chosen because they have been used successfully in these formations for years.

A 40-inch stabilizer placed one pipe joint behind the hole opener was recommended to keep the cutters true to the bore face. Three more stabilizers with diminishing diameters were recommended to support the drill string and reduce stress on the connections as the string dropped to the floor of the bore.

A short five weeks later, Transco delivered the custom-designed dual-stage hole opener to the customer.

Initial Delays

Once drilling of the second crossing began there were several delays due to equipment repairs and lost circulation. There were other challenges as well. About 7,000 feet into the hole the drilling fluid breached into the adjacent hole and the bore had to be completed without returns of the drilling fluid and cuttings. Drilling was interrupted many times while water was trucked in to make more drilling fluid. At about 9,000 feet the trailing drill string became stuck and required attempts over a period of several weeks to free it. Drilling was finally finished on Dec. 12, 2008.

Despite these challenges, the entire section was drilled without a single bit trip in just over 220 total drilling hours.

According to Transco officials, the cones on the 42-inch section had just over 1,560,000 revolutions. The bit graded out well with all seals effective and the contractor is reportedly planning on running it again before having the cutters replaced.

The 12¼-inch pilot hole was opened to 42 inches in a single pass with the custom-designed hole opener. This bore ran parallel and 33 feet to the side of the 32-inch bore that was completed in mid-2008 for the oil trunkline.

After a cleaning run and hole-conditioning procedures the pipe was pulled through in a 36-hour operation using the recently patented LFPP (Low Friction Pipe Pulling) procedure. The pull was completed on Jan. 12.
On completion of the project, the record-setting results reflect that a larger, more difficult bore was completed with a drastic reduction in trips, drilling tools, passes, resulting in a significant overall reduction in cost.

Much of the success of this and other recent record bores is due to a select group of HDD tool manufacturers dedicated to supplying engineered solutions for this unique industry. According to a Transco spokesman, with this new generation of tools, size and length records will continue to be set.