Drilling strategy, operations plan, and downhole measurements

To meet the scientific and engineering objectives, primary operations in Hole C0002F will comprise drilling using LWD/MWD to ~2300 mbsf, followed by setting 13⅜ inch casing (Fig. F3). Cuttings and mud gas will be collected and analyzed during riser drilling from 860.3 (bottom of 20 inch casing) to 2300 mbsf (see below regarding the 860–2005 mbsf section). Wireline coring will be conducted from 2300 to 2400 mbsf using a rotary core barrel (RCB) to obtain the highest quality and most complete core samples. Currently, plans call for drilling and LWD/MWD logging and cuttings and mud gas analysis to then continue to ~3600 mbsf, where the 11¾ inch casing shoe will be set. An alternative plan if conditions and time allow, is to drill with the same LWD string ~4400 mbsf and install a 9⅝ inch liner, as described above.

Operations plan

The operations plan and time estimate (Table T2) are based on formations and depths inferred from seismic and regional geological interpretations combined with data from previous drilling operations at nearby sites. We will use these operations and data to guide the operations described during Expedition 348. The primary operational plan is to conduct riser operations in Hole C0002F (Fig. F3).

Hole C0002F

During Expedition 326 in 2009, 36 inch conductor casing was run and cemented to 54 mbsf. Following this, a 26 inch hole was drilled to 860.3 mbsf, cased with 20 inch casing, and then cemented. During Expedition 338, the hole was deepened to 2005 mbsf in preparation for casing, but operations were terminated before the casing could be installed. Hole C0002F was suspended with a series of cement plugs and high-density mud: the section between 910 and 2007.5 mbsf was filled with 1.12 sg KNPP mud, above which was an ~72 m thick cement plug (1; 838.2–910.5 mbsf); another section was filled with high-density mud (1.12 KNPP) to another ~50 m thick cement plug (2; 350–400 mbsf), above which more high-density KNPP mud (1.12 sg) filled the space between it and the corrosion cap on the wellhead. During Expedition 348, we will begin drilling a sidetrack hole from within the cement plug below the 20 inch casing shoe, running LWD/MWD tools behind a 12¼ inch bit. The first drilling interval will be from 860.3 to 2300 mbsf to set and cement the 13⅜ inch casing (Fig. F3). After a leak-off test, we will perform RCB drilling and coring from 2300 to 2400 mbsf. A second LWD/MWD interval will extend the hole to 3600 mbsf, after which the 11¾ inch casing will be set and cemented. If time is available after setting the 11¾ inch casing, additional coring beyond 3600 mbsf may be included.