Drilling StrategyThe proposed Site WP-1B drilling program consists of coring two pilot holes (A and B) to characterize the site prior to a third hole (c), in which a reentry cone and casing string will be set and the ION instrument string installed. Time on site estimates to accomplish these objectives are ~26 days. Coring/drilling Holes A and B will consume 10.8 days including wireline logging. Installation and setting up the reentry cone and casing for Hole C is estimated at 7.5 days, with the remaining time on site devoted to the installation of the instrument and battery package (Fig. 5, Fig. 6). Should time permit we are planning to core a fourth hole (D) with the APC/XCB as deep as possible.
A reentry cone will then be assembled and lowered to the seafloor with ~60 m of 16-in casing
(actual length to be determined by a jet-in test after completion of Hole A). It will be washed to
depth and the reentry cone released on the seafloor. The drill string will then be recovered and a
drilling bottom-hole assembly (BHA) made up with a 14-3/4 in tricone bit. Hole C will then be
reentered and the hole deepened to ~425 mbsf. The drill string will again be recovered before
making up ~410 m of 10-3/4 in casing. The 10-3/4 in casing string will be cemented in place ~40
m into basement. The drill string will then be recovered and the final BHA to drill a 9-7/8-in hole
will be assembled. Because the instrument string should be located in a relatively homogeneous
and unfractured zone, the hole is planned to be ~100 m into basalt basement. Actual penetration
will be decided upon in the field. This decision will be based on information provided by the cores
and the wireline logs from Hole B, drilling data provided by the drillers, and the amount of
allowable time remaining in the program to complete the leg objectives.
After the hole is drilled to depth and the drill string recovered, the instrument package will be made up and attached to the 4-1/2 in deployment casing. The instrument package for Leg 195 consists of two seismometers (Fig. 5, Fig. 6). Centralizers will be equally spaced on the casing string to keep it centralized within the borehole. Once lowered into place, the instruments will be cemented in place through the drill string and support tubing. Afterward, the drill string will be disconnected from the hanger/riser, leaving it at a predetermined height above the reentry cone (Fig. 6). A battery package will then be lowered into the throat of the reentry cone (Fig. 6) on the logging line and accoustically released. Finally, the drill string will be released and recovered back aboard the drillship.
Sampling Plan | Table of Contents