162 Preliminary Report

Site 985

According to the plan in the Leg 162 Prospectus, the next site should have been EGM-4 on the East Greenland Margin. The ice data available to the shipboard party during the coring of Hole 907C showed that the EGM-4 drill site was positioned on the edge of the 20% ice concentration line. Just hours before getting underway, an updated special sensor microwave imager (SSMI) report was obtained which placed the EGM-4 drill site 20 nmi "outside" the 20% ice concentration line. Based on this promising report, and with a plan to survey alternate sites up to 10 nmi east of the proposed EGM-4 site, the vessel departed for EGM-4 at 1445 hr on 2 August 1995. Less than 1 hr after getting underway, a faxed "interpreted" synthetic aperture radar (SAR) image with data from 2 August 1995 was received which indicated that the EGM-4 drill site was 15 nmi "inside" what was referred to as "closed ice." In addition to being more recent, the SAR data is considered more accurate then the more general SSMI information. This new information made the EGM-4, as well as its alternate sites EGM-4a-d, essentially undrillable at that time.

In the normal course of events, we would have then proceeded to our next first-priority site, SVAL-1. However, we had to remain near Iceland to wait for resupplies of some critical items. The ship had only enough core liners onboard to complete a limited amount of coring (about 700 m) and was running very low on acetone. A resupply was scheduled to take place via rendezvous with the supply boat M/V Strakur prior to departure for the northern drill sites. Hence, the decision was made to steam towards ICEP-3, a second-priority alternate site. While underway, the computer file containing the SAR photo was picked up from the ODP directory, and the interpreted information received earlier regarding EGM-4 ice conditions was confirmed.

The drilling plan for ICEP-3 (Site 985) was to core a single APC/XCB hole as deep as possible in the time before the resupply ship arrived. The Pollution Prevention and Safety Panel (PPSP) had approved drilling to a depth of 500 mbsf, but the co-chiefs felt that any major scientific rewards would most likely be attained at deeper depths. As a result, they asked for and received permission to extend the depth of Hole 985A to 650 mbsf, time permitting. No core orientation or temperature measurements were to be taken at this site.

After completing the presite survey, the vessel returned to the coring location based on GPS coordinates. The positioning beacon was deployed at 1358 hr on 3 August 1995, initiating Hole 985A.

A standard APC/XCB BHA was used for all holes at Site 985, including a non-magnetic drill collar. The mudline was established for each hole. The APC firing depth was offset by a few meters for Hole 985B relative to Hole 985A in order to establish a continuous sediment section over the double-cored interval. Position, depths, and coring totals for each hole are summarized at the top of this chapter.

Routine piston coring at Hole 985A proceeded until Cores 985-14H through 17H failed to bleedoff pressure, indicating incomplete stroke. Extended Core Barrel (XCB) coring was initiated with Core 985A-18X and continued with excellent recovery. Coring was temporarily halted when the methane/ethane ratio dropped from 100,000+ in Core 985-36X to 6 in Core 985-37X; gas concentrations were very small. In addition to the abrupt reduction in gas ratio, trace amounts of higher hydrocarbons up through IC6 were detected. At that time cutting of Core 985A-40X was just completed and coring operations were halted until additional analyses could be evaluated. The hydrocarbon trends returned to normal in Cores 985A-38X and 39X, and the results from Core 985A-40X were completely back to normal. Throughout the coring cycle there were no changes in formation properties or coring parameters. Coring resumed and continued without incident through Core 985A-62X when the scientific target was reached.

Upon completion of coring operations a wiper trip was made in preparation for wireline logging. Overpull of 30,000 to 50,000 lb was experienced, and 9 m of fill were identified on bottom. The hole was again circulated with two annular-hole volumes of seawater while the go-devil was pumped downhole. The pipe was then pulled to a logging depth of 90.1 mbsf with 10,000 to 20,000 lb of drag. Wireline logging was not successful in this hole. The first logging run, which ran the Quad combo, was only able to get to 23 m below the bit, and all efforts to exceed that point failed. After a consultation with the co-chief scientists and the loggers, it was decided that any further logging attempts on Hole 985A be abandoned.

The vessel was offset 15 m north for spudding Hole 985B. APC coring proceeded without incident until the last remaining core liner was used on Core 985B-14H. Fortunately, the supply boat was expected within a few hours.

While waiting for the supply boat, the drilling line was cut and slipped prior to tripping the drill string back to the vessel. During the trip, the supply boat M/V Strakur arrived (1715 hr). After several unsuccessful attempts to come alongside due to "thruster wash" the captain decided to release the beacon, retract the hydrophones, and turn the vessel to give the supply boat more of a lee to come alongside. During the process the drill ship was allowed to drift with the current. The beacon was recovered at 1820 hr, and at 1845 hr the M/V Strakur was alongside, discharging her cargo.

The core liners, acetone, mail, and other requested supplies were taken aboard. Shipboard mail and a small airfreight package were discharged to the supply boat along with a Borehole Research Group logging trainee who had elected to leave his field of study and requested to return to shore. At 1915 hr on 7 August, the Strakur departed for a small harbor just north of Reykjavik.

The pipe trip continued throughout the loading/unloading process, and at 2115 hr that same day the vessel was secured and underway for Site 986 (SVAL-1).

To Operations Site 986

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