OPERATIONS

Transit from Site 1208 to Site 1209

The 210-nmi transit to Site 1209 was made in 18.4 hr at an average speed of 11.4 kt. Upon arriving on site, the thrusters and hydrophones were lowered, and the ship was switched over to dynamic positioning mode, initiating Site 1209 at 0755 hr on 18 September.

Hole 1209A

An APC/XCB bottom-hole assembly (BHA) was assembled, and the bit was positioned above the seafloor at 2397.0 meters below rig floor (mbrf). Hole 1209A was officially spudded at 1405 hr on 18 September, recovering 8.21 m, which established a seafloor depth of 2398.3 mbrf, or 2387.2 meters below sea floor (mbsl) (Table T1). APC coring continued through Core 26H to a depth of 245.7 mbsf. An incomplete stroke on Core 26H led to abandoning APC coring in favor of using the XCB. Recovery with the APC averaged 101.9%. Cores 4H through 26H were oriented. Coring with the XCB continued through Core 198-1209-28X to a depth of 259.6 mbsf. Coring was terminated after 30 min of rotating time on a hard layer, presumably chert, with no advancement. The drill string was tripped up, clearing the seafloor at 1335 hr on 19 September, ending drilling at Hole 1209A.

Hole 1209B

After offsetting the drill ship 15 m north, the drill string was spaced out with the bit placed 3.0 m higher than the spudding depth of Hole 1209A. Hole 1209B was spudded at 1454 hr on 19 September. Recovery on the first core measured 5.16 m, yielding a seafloor depth of 2398.4 mbrf, or 2387.4 mbsl. APC coring advanced to a depth of 297.6 mbsf through Core 32H with 98.2% recovery. Cores 4H through 32H were oriented, and Adara temperature shoe deployments were made on Cores 6H, 8H, 10H, and 12H. Three of the Adara tool measurements were good quality, but the tool deployed with Core 6H failed. Core 32H was not a complete piston stroke; hence, an XCB center bit was deployed to drill through the presumed chert layer. With 1.5 hr of rotating time and only 0.4 m advancement, we decided to terminate coring in Hole 1209B. While attempting to recover the XCB center bit, we discovered that a sub on the pulling tool had backed off. In addition, the forward wireline was damaged, which required 150 m of line to be removed. While effecting repairs, the aft wireline was used in an attempt to fish the core stub of the pulling tool. However, after two unsuccessful attempts, we had to trip the drill string back to the ship, clearing the rig floor at 0710 hr on 21 September and ending drilling at Hole 1209B.

Hole 1209C

The ship was offset 15 m east of Hole 1209A, and Hole 1209C was spudded at 1155 hr on 21 September. The hole was drilled to a depth of 98.0 mbsf, and then APC coring was initiated, continuing to a depth of 251.5 mbsf. At this depth, Core 17H contacted chert after stroking ahead only 1.5 m. An XCB center bit was deployed, drilling ahead to 252.5 mbsf. APC coring resumed (Cores 198-1209C-18H and 19H), progressing to 264.9 mbsf before encountering another chert layer. The XCB center bit was used to drill ahead to a depth of 268.4 mbsf. The next APC core barrel (Core 20H) failed to fully stroke, and shear pins in the overshot connecting the nonmagnetic sinker bars failed. This barrel was recovered after a second wireline run, and core orientation activities were suspended to avoid further complications with the nonmagnetic components. APC coring continued with Cores 21H and 22H to 296.9 mbsf, where a chert layer impeded progress. The XCB center bit was deployed and used to advance the hole through chert to 299.7 mbsf. While attempting to shoot APC Core 198-1209C-23H, the pins failed to shear and the barrel did not penetrate into the formation. Upon recovery, this barrel was inspected and seals were changed to ensure that the barrel was functioning correctly. It was redeployed, but the pins did not shear again. We then switched to the XCB to determine if the problem was related to the APC barrel or the BHA. XCB Core 23X was advanced to 307.5 mbsf; however, despite latching properly, the barrel was recovered empty. A final APC core was attempted, but the APC barrel could not be landed correctly. Convinced that there was a mechanical problem with the bit and/or lockable float valve (LFV), coring was suspended, and the drill string was retrieved. Total recovery for Hole 1209C was 99.2%, with APC recovery averaging 103%.

At 0425 hr on 23 September, the pipe cleared the rotary table on the rig floor, ending operations at Site 1209. A subsequent inspection of the coring assembly showed that the primary bit was heavily damaged on the inner row cutters and that the flapper hinge pin in the LFV was broken (Fig. F5). Chert was found behind the flapper, likely preventing it from fully opening when the core barrels attempted to pass through. This resulted in overloading the flapper hinge, leading to the failure.

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