Drilling and coring plan

We will depart the port of Hachinohe and move to Site C9001 (41°10.5983′N, 142°12.0328′E). After the seafloor survey by remotely operated vehicle, we will deploy transponders on the seabed, and then spud in the suspended hole, where 20 inch casing pipes were previously installed to 511 mbsf. The corrosion cap will be retrieved, and a blowout preventer (BOP) and riser pipes will be connected to the borehole. We will conduct riser drilling to 1220 mbsf with spot coring using rotary core barrel (RCB). The spot coring is planned every 150 m, at the following four depth intervals: 670–679.5, 820–829.5, 970–979.5, and 1120–1129.5 mbsf (Tables T1, T2). Then the first series of wireline logging runs will be performed for the depth interval between 647 and 1220 mbsf before installing 13⅜ inch casing pipes (see "Logging, downhole measurements, and in situ sampling plan").

From 1220 mbsf to the target depth of 2200 mbsf, we will continue riser drilling to take cores at the following depths: 1270–1279.5, 1370–1379.5, 1470–1479.5, 1581.5–1648, 1648–1675, 1770–1789, 1870–1889, 1933–1990, 1990–2044, 2140–2149.5, and 2190.5–2200 mbsf. The coring at 1648–1675 and 1990–2044 mbsf will utilize large diameter coring (LDC) systems (Baker Hughes INTEQ, Inc.) (Table T1). The LDC systems provide core material that is 10 cm (4 inch) in diameter and up to 27 m long. The LDC system is equipped with either a Hydrolift or Jam-Buster system, which improves core recovery, particularly in problematic lithologies such as brittle lignite. Core retrieval by the LDC system requires pipe trip, not wireline trip, and is contained in an aluminum inner tube. The LDC system will be used for two critical intervals: one corresponding to the Eocene–Oligocene unconformity and the other for the central part of the Eocene unit that contains the lignite layers. After reaching the target depth of 2200 mbsf, we will conduct the second series of wireline logging, including in situ sampling of the formation fluids. The hole will be suspended by cementing without additional casing pipe installation.

After completion of the riser hole, we will conduct coring at Site C9001 by Hybrid-PCS. Hybrid-PCS contains a bearing and a nitrogen-charged pressure regulator section, enabling recovery of a 54 mm diameter × 3.5 m long core under in situ pressure conditions. Using the Hybrid-PCS, we will collect spot-core samples at several representative depth intervals (0–3.5, 10–13.5, 100–103.5, and 206.5–231 mbsf) (Table T1). During riserless Hybrid-PCS operations, formation temperature is measured with the advanced piston corer temperature tool (APCT-3) at selected depth horizons. Retrieved cores are transferred without pressure loss into an aluminum chamber in the Pressure Core Analysis and Transfer System (PCATS) (GeoTek, Ltd., UK). The PCATS enables us to measure P-wave velocity and gamma density, as well as nondestructive 2-D and three-dimensional (3-D) X-ray computed tomography (CT) images (Schultheiss et al., 2009).

The currently projected depth intervals for coring are shown in Table T1. We intend to recover sediments from all representative lithologies. At the same time, relatively regular spacing of spot coring is useful to obtain reliable variation of physical properties with depth. Actual coring intervals are subject to change on board the ship based on initial results of coring and observation of cuttings and logging data. Analysis of cuttings, cored sediments, log data, and seismic integration will be an important task of the science party.