On one occasion, two each 8-1/4" drill collars were bent ~2 m from their respective pin/box ends. While pulling out of the hole after core bit run #9, the drill bit hung up on a ledge during a down heave putting the BHA into compression. The resultant buckling of one connection caused the box end of collar #2 and the pin end of collar #3 to be bent. Due to deteriorating weather conditions, we were tripping the drill string back to the surface. We had just pulled a stand of 5" drill pipe placing the bit at a depth of 739.0 m or 8.0 mbsf. The string was landed in the elevators, but still attached to the top drive, when the bit came in contact with a ledge in the hole. This caused the full weight of the drill string to be applied to the bit, and the drill string jumped upward in the landing elevators. The string was lifted off of the elevators ~2.0 m where the bit was free from contacting the ledge. After two attempts, we finally were able to lower the string past the ledge to the next tool joint. A double of drill pipe was laid out of the string, and we then pulled a full stand of pipe allowing the bit to clear the seafloor/HRB.
At the surface, two 8 1/4" drill collars # 2 and #3 (1st and 2nd DCs above the outer core barrel assembly) were found to be slightly bent at their respective box/pin ends, indicating that this connection had been placed in compression and buckling had occurred. The two bent drill collars were replaced, and the entire BHA was inspected with no crack indications found. To avoid the potential for a reoccurrence of the incident, both drill crews were instructed to space out in a similar manner during all reentry operations and when pulling the bit clear of the seafloor. This avoided placing the bit in the suspect portion of the hole while making or breaking connections at the rig floor. In this case, the problem was aggravated by significant heave during the drill string retrieval. At the time, the wind was blowing 33-41 kt and gusting to 51 kt. Swells were running 8'-18' at 8-9 s periods and vessel heave was 10-18 ft. An Incident Report was submitted and the two drill collars were returned to shore to be used for sub stock.
On another occasion, a pin thread on a joint of 5" drill pipe failed while short tripping wear-knotted drill pipe from the hole. Subsequently, the pipe being fished failed again, this time in the 5" tube body. The drill string was being pulled with the top drive during a routine wiper trip to change out five stands of 5-1/2" wear-knotted drill pipe. The drill string was landed in the elevators while a double of drill pipe was being put into the mousehole with the top drive. During this operation, the drill string twice came into contact with a ledge in the hole when the vessel heaved down. This caused the string to rise ~18" above the landing elevators. The top drive was made back up to the drill string as quickly as possible, and the string was lifted off of the landing elevators. At this point, the weight indicator showed a loss of 130K lb of string weight. Initial calculations indicated that the string parted in the 5" drill pipe at or near the seafloor. We deployed the subsea camera to inspect the drill string/HRB and ensure that the failed pipe was not above the seafloor.
When the drill string was recovered, we found the point of failure to be at a pin connection in the 5" drill pipe when it was located at 739 m or 8 mbsf. The fish left in the hole was 1403 m in length and consisted of the BHA (172 m) plus 43-2/3 stands of 5" drill pipe (1231 m). A 9-1/2" overshot dressed with a 6-7/8" basket grapple with mill control was used to engage the fish at a depth of 838 m (107 mbsf). As we lifted the fish to its total weight of 130K lb, it failed again leaving only 35K lb of weight suspended below the overshot. The fishing string was pulled to the surface where a total of 497 m of 5" drill pipe was recovered below the overshot. The fish parted in the tube of the 5" drill pipe two feet below the box tool joint at a point where the tube had buckled when the string impacted the bottom of the hole. The portion of fish remaining in the hole (906 m) consisted of 26 stands of 5" drill pipe (734 m) and the coring BHA (172 m). Subsequent milling/fishing operations were unsuccessful in engaging or removing the remaining junk from the hole. Weather conditions at the time of failure were not particularly bad, although vessel heave was in excess of 2 m. The wind was blowing at 24-30 kt, seas/swells were running 11-12 ft at 7-9 s periods, the average roll was 3° (maximum 6°), and the average pitch was 2° ( maximum 5°). Vessel heave was approximately 8 ft. The remaining 51 joints of 5" drill pipe recovered from the hole were identified with a double yellow band. The 21 joints of 5" pipe that were above the failure point were identified with a single yellow band. All of this 5" pipe was stored in the previously empty starboard 5" pipe racker. Additional 5-1/2" pipe to be inspected during the post Leg 176 Cape Town port call was not marked but included the top 21 stands (63 joints). Of this pipe, four stands (12 joints) had aluminum wear knots installed.
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