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doi:10.2204/iodp.pr.340.2012

Operations

Site U1393

We planned to core two holes at Site U1393 and recover as much of the young debris avalanche deposit (Deposit 1) of the Soufrière Hills Volcano on Montserrat as possible. However, because of unfavorable drilling conditions encountered at this site, only one hole was drilled. The hole was cored to 47.55 mbsf with an 11 inch diameter APC/XCB core bit and a 135.75 m long bottom-hole assembly (BHA). An APC mudline core established a water depth of 926 mbsl. The second APC core bounced off the formation, and the APC system was changed over to the XCB coring system. Coring conditions proved to be very difficult, and recovery was very poor. Coring was terminated when the XCB system failed, leaving part of the XCB core barrel in the hole. The depth objective at the site was 250 mbsf, and this appeared to be unreachable with the tools planned for the site. Overall core recovery for Site U1393 was 11.4% of the 47.5 m cored (5.42 m of material). Logging was not conducted at this site.

Site U1394

The vessel arrived at Site U1394 after a 5.3 nmi transit in dynamic positioning mode from Site U1393. Site U1394 consists of two holes. The original plan called for two holes cored to ~244 mbsf. Hole U1394A was advanced 235 m into the formation, whereas Hole U1394B was shortened to ~180 mbsf from the start of drilling because of challenging coring conditions, after ensuring that the lowermost 60 m at this site was scientifically less interesting to the Co-Chief Scientists. Hole U1394B was successfully logged with the triple combo and FMS-sonic logging strings. The VSP experiment was canceled when all efforts to deploy the VSI through the BHA were unsuccessful. Forty-eight cores were retrieved in Holes U1394A and U1394B with average recovery rates of 23% (57 m of material) and 78% (162 m of material), respectively.

Site U1395

Site U1395 consists of two holes. The original plan called for two holes cored to ~244 mbsf. Because the coring was challenging and took slightly longer than originally anticipated, the first hole was shortened to 231.3 mbsf. The second hole was shortened to 203.3 mbsf because of time constraints. Hole U1395B was successfully logged with the triple combo and FMS-sonic logging strings. Fifty-three cores were recovered at this site with an average recovery rate of 62% for Hole U1395A and 69% for Hole U1395B, retrieving a total of 284 m of material.

Site U1396

Site U1396 consists of three holes. The original plan called for two holes to ~132 mbsf. Hole U1396A was successfully cored to 134.9 mbsf. Hole U1396B was a shallower penetration hole designed to capture a poorly recovered interval in Hole U1396A. The second core from Hole U1396A was recovered with a shattered core liner; Hole U1396B reached 15 mbsf. Hole U1396C was cored to 139.4 mbsf. Because of the shallow penetration, no downhole logging was scheduled at this site. The APC coring system was deployed 31 times, penetrated 283.8 mbsf, and recovered 296.38 m of core (104% recovery). A single 5 m interval was drilled without coring in Hole U1396B.

Site U1397

Site U1397 consists of two holes. The original plan called for two holes cored to ~314 mbsf. The first hole, Hole U1397A, was successfully cored but was terminated at 265.5 mbsf. The second hole, Hole U1397B, was cored to 253.5 mbsf. Hole U1397B was successfully logged with the triple combo and FMS-sonic logging strings. The planned VSP experiment was canceled, as the diameter of the hole proved too large to use the VSI. Sixty-six cores were retrieved at this site, and two short intervals had to be drilled without coring. Thirty-five APC cores penetrated to 225.7 mbsf and recovered 226.17 m (100%). Thirty-one XCB cores penetrated to 284.1 mbsf and recovered 49.49 m (17%). Overall recovery for Site U1397 was 54.1%.

Site U1398

Site U1398 consists of two holes. The original plan called for two holes cored to ~264 mbsf. Hole U1398A was successfully cored and was terminated at a total depth of 268.6 mbsf. Hole U1398B was cored to 263.4 mbsf. Downhole logging was planned, but hole problems encountered during the first logging attempt forced the cancelation of all logging. In total we retrieved 64 cores with 302 m of material (57% recovery). Total time spent at Site U1398 was 103.5 h.

Site U1399

Site U1399 consists of three holes. The original plan called for two holes cored to ~290 mbsf. The first hole was successfully cored and was terminated at 275 mbsf. The second hole was piston cored to 183 mbsf and abandoned when the hole became too unstable to continue coring operations. Thus the logging operations planned for this hole were abandoned as well. Instead, the decision was made to drill a dedicated logging hole to 240 mbsf: Hole U1399C. The logging program, including the triple combo, FMS-sonic, and VSI tool strings, was completed as planned. A total of 393 m of core (101% recovery) was obtained with the APC, whereas 9 m of core (14% recovery) was obtained with the XCB. Overall core recovery for Site U1399 was 89%. Total time spent on Site U1399 was 160 h.

Site U1400

Site U1400 consists of three holes. The original plan called for two holes cored to ~510 mbsf. The first hole was terminated at 51.3 mbsf because of unstable hole conditions. After offsetting the vessel 750 m in a direction 160° from Hole U1400A, the second hole, U1400B, was piston cored to 212.5 mbsf. After the core barrel became stuck, the drill string had to be tripped to surface and the core barrel freed from the upper landing sub. A shear pin had become wedged between the removable landing seat and the core barrel assembly. After offsetting 20 m further in a 160° direction, the third hole of the site began with two failed attempts at spudding Hole U1400C. The first failed attempt broke off the lower section of a nonmagnetic core barrel with the cutting shoe. After the core barrel was retrieved and the breakage was discovered, a steel core barrel was installed and run to bottom. The second attempt was even less successful. This time the steel barrel bent in such a fashion that it was not possible to pull it back through the BHA. The drill string was again pulled to the surface, the bent core barrel was cut away, and the BHA was reassembled for another attempt. This time, the hole was advanced 15 m into the seafloor before running in with the wireline to begin coring. APC coring continued through Core 340-U1400C-22H at 191.1 mbsf. APC coring was terminated when the formation became so stiff that the core liner folded up inside the core barrel and had to be pumped out with a 10,000 psi pump. The XCB was then deployed and used to successfully complete coring operations to 436 mbsf. Logging was planned for Hole U1400C, but hole problems, which resulted in a severed BHA, forced the abandonment of the hole. The APC was deployed 58 times, recovering 447 m of material (102% recovery). The XCB was deployed 27 times, recovering 124 m of material (51% recovery). Overall recovery for Site U1400 was 84%. Total time spent on Site U1400 was 207 h.

Site U1401

Site U1401 consists of four holes. This proposed site (CARI-12A) was originally an alternate site to proposed Site CARI-07C, but was felt to be a better fit with expedition objectives in the remaining expedition time. The original plan called for two holes cored to ~500 mbsf. With the limited time remaining, the site was reprogrammed for a single hole to ~350 mbsf. The first hole was terminated at 82 mbsf because of unstable hole conditions. It was apparent from the difficult drilling conditions and the time remaining that a new plan was needed. The plan was modified to core a transect on 300 m centers along the Aguadomar seismic line running along a 062°/242° line. In all, four holes were cored at the site. Holes U1401B and Hole U1401C were cored with three piston cores, and the final hole, U1401D, had a single 9 m core recovered before time expired. The APC was deployed 11 times. The cored interval with the APC was 47 m with a recovery of 46 m of core (99% recovery). The XCB was deployed seven times. The cored interval with the XCB was 67 m with a recovery of 1 m of core (2% recovery). Overall recovery for Site U1401 was 42%. Total time spent on Site U1401 was 53 h.

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