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.