5,675-Foot x 72-Inch HDD Bore for 48-Inch Pipe Sets New Record

By Ben Boere, Project Manager, FlowTex Egypt and Roy Estes, Chief Engineer, Transcontinental Supplies Inc. | March 2011, Vol. 66 No. 3

FloTex had just completed a difficult HDD mountain crossing in Madagascar. Midway through that project they had switched to a barrel type hole opener and saw major improvements in penetration rate, tool life and hole condition. They were also aware that in 2008, a barrel type hole opener was used in a record setting 42-inch, 3,050 meter bore in Saudi Arabia in similar formation conditions.

As a result, a decision was made to use the barrel type hole openers with mill tooth cutters on this project. In consultation with the hole opener manufacturer, Transco Mfg. Australia, tools were ordered to open the holes in 26-, 36-, 44-, 58- and 72-inch stages.

The new tools were ordered at such a late stage in the project the pilot hole had almost been completed. This resulted in the reaming having to be started with barrel reamers with pick cutters. As was expected, reaming in the hard sections was extremely slow, and some joints of the drill pipe required two hours to complete.

When the first barrel hole opener arrived it was installed with barrel reamers in the front and at the back. The milled tooth cutters proved able to drill the hard sections much faster than the pick cutters and did not ball up in the soft sections. The rate of penetration was about 30 minutes per joint and could have been faster in some areas if the mud volume could have handled the cuttings. All the hole openers were run with barrel reamers before and after. This bottom hole assembly centralized and stabilized the hole opener and tended to straighten small deviations in the bore. Throughout the job the pull force varied from five to 50 tons, the rotations per minute ranged from 25 to 50 and the mud flow was from 475 to 660 gallons per minute. The sites were active 24 hours a day.

The standard design for the barrel hole openers worked very well up to 58 inches. At that point there was concern that the weight of the 72-inch hole opener would be too much for the softer sections of formation. FlowTex project manager, Ben Boere, along with a Transco sales technician suggested a lighter weight design for the 72-inch tool. In a few weeks time the new tool was produced and air freighted to the jobsite. The light-weight tool worked very well. The torque and pull values were low and the penetration rates were similar to those of the smaller hole openers.