Inspection Detail

Inspection: 309786689 - Patterson-Uti Drilling Company

Inspection Information - Office: Oklahoma City Area Office

Investigation Summary

On July 6, 2006, Employees #1, #2, and #3 were drilling an oil and gas well. They were preparing to insert a 30-foot section of drilling pipe into the nearly 6,500-foot-long drilling string. Their coworker, the driller, was operating the draw works. He had pulled most of the kelly out of the well, when he felt a bump. Employees #1 and #3 were on the west side of the drill rig, preparing to connect the kelly to the new section of drill pipe, while Employee #2 was on the racking board, preparing the power tongs to disengage the kelly from the string. Suddenly, there was a loud noise, and the crown sheave shaft came out of one of its mounts, allowing the five sheaves, the drilling line, the 165,000-pound drilling string, and the blocks to fall to the drilling floor. Employee #1's right leg was trapped under the blocks and nearly amputated. He sustained severe blood loss, and he was killed as a result of his lacerations. Employee #2 was under Employee #1 and suffered a head wound. He was hospitalized for his lacerations. Employee #3 had a head wound and multiple right leg fractures. He was hospitalized too. The driller had minor abrasions and contusions. This is no mention of him on the injury lines. The reason that the shaft pulled out of one of its pillar blocks was that the shaft retaining bolt (similar to a set screw) did not sufficiently penetrate the shaft receptacle. This oversight allowed the end of the shaft move about and enlarge the pillar block shaft hole. After a while, the shaft end could move in and out of the pillar block, until, by the time of the accident, the shaft pulled entirely free of the pillar block. Then the second pillar block's supporting steel structure failed, letting the freed shaft end deflect downwards and allowing the unrestrained sheaves to fall. Underlying these failures were inadequate inspections of the mast, including the crown assembly. The moving shaft had distended the pillar block, causing an observable gap between the two. Two cracks, not associated with the accident, were observed on the crown structure. Two bolts and a nut were found on the crown after the accident; their placement could not be ascertained, and they were not damaged. The mast secondary structure had numerous sections bent or otherwise damaged; the employer, upon completion of an in-depth inspection, replaced upwards of twenty-five percent of the upper mast secondary structure.

Keywords: HEAD, INADEQUATE MAINT, DRILL PIPE, KELLY BUSHING, LACERATION, DRILL RIG--NON-OIL, STRUCK BY, FALLING OBJECT, OIL RIG, LEG