OPERATIONS SYNOPSIS (continued)

The ship rendezvoused with the pilot boat, and three new personnel (two from ODP and one from Overseas Drilling Limited) were transferred on board along with some light cargo. Two personnel, an ODP engineer and a technical representative from Maritime Hydraulics, left the vessel. At 1255 hr, the transfer was completed and the JOIDES Resolution altered course and continued to the next site. The vessel proceeded on a southerly course for the 270-nmi transit, which was accomplished at an average speed of 11.3 kt.

Hole 1169A
At 1245 hr on March 28, a beacon was deployed, hydrophones and thrusters were extended, and the vessel settled on location. An APC/XCB BHA was made up and run to near the PDR depth of 3584.4 mbrf.

As the drill string was being deployed, a cold front passed over our location, driving the winds from 28 kt to >55 kt in the space of a few minutes. Accompanying the arrival of the front were very heavy rains and a drop in temperature of 4°C in <15 min. Although the intensity of the winds quickly abated as the direction shifted from the north to the west, the resulting conditions from the passage of the front strongly affected subsequent coring.

Hole 1169A was spudded with the APC at 2245 hr on 28 March. The seafloor depth was calculated from the recovery of the first core and determined to be 3578.9 mbrf, or 3567.9 mbsl. As piston coring was initiated, the weather deteriorated and generated considerable vessel motion that adversely affected the quality of the cores. During coring in this hole, the winds were predominantly from the west and never dropped below 22 kt with gusts frequently measured between 35 and 40 kt. There was also a complex swell from the west and southwest (~5 m amplitude) that would periodically combine and push the vessel heave >6 m.

The weather made for difficult operations with resulting poor quality of the piston cores. During operations, the wireline had to be re-terminated at the rope socket twice because of fraying steel-rope members arising from an excessive bending radius caused by excessive vessel motion. Two additional wireline roundtrips were needed to fish out the core barrel when the wireline eventually parted at the rope socket. On another occasion, coring had to be stopped for several hours while the drill crew disassembled the piston corer to clean out a core liner that completely failed, likely a result of the extreme hydraulic forces. The wireline speed was also reduced to accommodate the weather-induced motion of the drill string and vessel.

The quality of the cores was poor due to the flow-in and vertical disturbance caused by the dynamics of attempting to piston core in this environment. During piston coring, the heave compensator is not used except for drilling or washing ahead to position the drill bit for the next piston core attempt. When the piston corer is fired, the heave compensator is locked and the bit is forced to follow the vertical motion of the vessel. It was expected that as soon as XCB coring was initiated, the core quality would improve because of the activation of the heave compensator with a resulting decrease in core disturbance. Unfortunately, the main objective for this site was recovery of an upper Neogene section for high-resolution analysis that only undisturbed APC cores could provide.

After the APC coring advanced to a depth of 199 mbsf, we switched to the XCB system in an attempt to minimize core disturbance, despite the fact that only minimum pull-out force was required to free the core barrel from the sediment. Coring concluded when the XCB deepened the hole from 199 mbsf to the depth objective of 247 mbsf. The main goal for this site was high resolution analysis of the sedimentary record; hence, operations were terminated because of the effect that the sea state was having on core quality. The average recovery of the piston-cored section of the hole was 100%, with overall recovery being 91%.

The drill bit was pulled clear of the seafloor at 0200 hr on 31 March and the drill string was recovered. As the BHA was being disassembled into the component drill collars in preparation for the transit to the next site, the beacon was successfully recovered. Following the retraction of the thrusters and hydrophones and the securing of the drilling equipment, the vessel began the short transit to the next site at 0830 hr on 31 March.