Technical Note 25

OPERATIONS SUPERINTENDENT'S PERCEPTION OF LEG 153

920A (Site MK-2) Water depth: 3339 m; Total penetration: 14.0 m

Hole 920A was initially overcored to 14 mbsf without any significant hole problems. While retrieving the first core barrel, the bit became plugged and the hole began packing off. The core barrel and wireline became stuck inside the bottom hole assembly. The wireline had to be severed to be recovered. The drill string then had to be recovered to remove the stuck core barrel, thus ending Hole 920A.

920B Water depth: 3339 m; Total penetration: 126.4 m

Hole 920B produced high, erratic torque throughout the coring operation. No other significant hole problems occurred. While pulling out of the hole to replace the bit (43-3/4 rotating hours on the bit) the bottom hole assembly became stuck at 112 mbsf. The drill string was worked 6 hrs before it came free. After reentering via a modified free fall funnel, the hole was reamed to 26 mbsf. It was determined that a new hole was being made and the hole was abandoned.

920C Water depth: 3343 m; Total penetration: 16.0 m

The hard rock base was deployed 10 m south of Hole 920A. The initial slope, as indicated by a tilt beacon attached to the base, was 16°. The base was moved 5 m east where the indicated slope was 10°. During the round trip for the drilling assembly, the base settled, tilting over 2.6°. While drilling a 17-1/2 in. hole to 16 mbsf, the base settled an additional 1.3°. While conditioning the hole in preparation for casing, the base settled 1.9° more. The base was now leaning against the bottom hole assembly, preventing the bit from being worked to the bottom of the hole. During the round trip for the running tool, the base settled an additional 2.6° for a total of 8.4° (Figure 2). While attempting reentry, the base reentry cone toppled over and would not right itself. Finally, with the use of a "rig fabricated" stabilizer, the base reentry cone was righted, reentered and latched into. The base was then successfully recovered for repairs, ending Hole 920C.

920D Water depth: 3338 m; Total penetration: 200.8 m

Hole 920D produced high, erratic torque below 125 mbsf. Constant hole reaming was required below 175 mbsf. The drill string became stuck at 182 mbsf and subsequently freed. At 200 mbsf the hole began packing off faster than it could be cleaned. As the bottom hole assembly was being pulled from the hole, it became stuck at 190 mbsf. The drill string eventually had to be severed, ending Hole 920D.

921A (Site MK-1) Water depth: 2488 m; Total penetration: 17.1 m

Hole 921A was cored once to 17.1 mbsf with persistent high erratic torque throughout the coring operation. The hole was abandoned due to the high torque and hole fill.

921B Water depth: 2490 m; Total penetration: 44.1 m

Hole 921B produced high, erratic torque with continuous hole fill. Excessive reaming was required to keep the hole open. The hole was abandoned due to deteriorating hole conditions.

921C Water depth: 2495 m; Total penetration: 53.4 m

Hole 921C produced high, erratic torque while coring. No recovery was achieved in an apparent fault zone from 39 to 53.4 mbsf. This zone also appeared to be taking fluid. The hole was abandoned due to deteriorating hole conditions below the fault zone.

921D Water depth: 2514 m; Total penetration: 48.6 m

Hole 921D produced high, erratic torque with hole fill. Apparently, the same fault zone as encountered in Hole 921C was penetrated. The hole was abandoned due to deteriorating hole conditions below the fault zone.

921E Water depth: 2456 m; Total penetration: 76.8 m

Hole 921E produced high erratic torque and continuous hole fill. Excessive reaming was required. Frequent mud sweeps were used with only marginal success. The hole was abandoned due to deteriorating hole conditions.

922A Water depth: 2612 m; Total penetration: 14.6 m

Hole 922A produced high erratic torque with low penetration rate (0.3 m/hr). The hole was abandoned in preparation for a second attempt to deploy a hard rock base.

Second Hard Rock Base Deployment Attempt

The hard rock base was tripped to the seafloor without incident (Figure 3). The base was set down 13 times without finding a slope angle less than 20°. The effort was finally abandoned and the base was recovered.

922B Water depth: 2612 m; Total penetration: 37.4 m

Hole 922B produced high erratic torque with low penetration rate (0.3 m/hr). With 75 rotating hrs on the bit, the drill string was recovered to replace the bit. The hole was reentered and reamed to 12 mbsf when the bottom hole assembly, top sub box, failed, leaving the outer core barrel assembly in the hole.

923A Water depth: 2440 m; Total penetration: 70 m

Hole 923A produced high erratic torque with low penetration rate (0.3 m/hr). Good core recovery was achieved in the upper 50 m. Excessive reaming was required in the lower 20 m. Hole fill on connections increased near the bottom. At 70 mbsf, the hole packed off and had to be abandoned.

924A Water depth: 3170 m; Total penetration: 10 m

Hole 924A produced high erratic torque from the outset. With the bit at 10 mbsf, the first drill collar above the outer core barrel failed through the zip lift groove. The failure occurred 12 m above the seafloor, resulting in loss of Hole 924A.

924B Water depth: 3176 m; Total penetration: 30.8 m

Hole 924B produced high erratic torque from the outset. At 30.8 mbsf, 40,000 lbs overpull was required to free the bottom hole assembly and the hole was abandoned.

924C Water depth: 3177 m; Total penetration: 48.5 m

Hole 924C was cored at a low penetration rate (0.3 m/hr) to a depth of 48.5 mbsf with no significant hole problems. The hole was abandoned when the allotted coring time expired.

Leg 153 Operations Generalizations

The following operational generalization are made from a "rig floor" point of view.

End of Leg 153 - Operational Thoughts and Suggestions

The following are "thoughts and suggestions" for improvements to the current plan of attack for coring areas such as MARK in the future.

To Scientists' Perception of Leg 147 Operations

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