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

March 2009 Vol. 64 No. 3

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 to 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. The drilling was finally completed 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.