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doi:10.2204/iodp.sp.322.2009 Operations plan/drilling strategyOur primary objectives are to take cores, obtain downhole in situ formation measurements, and to conduct wireline logging through the entire stratigraphic succession of Shikoku Basin. Our operations plan and time estimate for proposed Site NT1-07A are shown in Table T1. Under normal circumstances, coring progresses from hydraulic piston coring system (HPCS) to extended shoe coring system (ESCS) coring (until refusal) to standard rotary core barrel (RCB) coring to obtain the highest quality, most complete core samples. Because of the need to obtain undeformed cores from the lowermost Shikoku Basin and the constraints of time, we plan to wash down to ~400 mbsf and begin coring using RCB. Following coring to basement, we will run downhole wireline logging measurements. If time permits after successful penetration of basement, we will core the upper 400 m using HPCS/ESCS. APCT-3 (formation temperature) and SET-P (formation temperature and pressure) measurements will be conducted during coring operations. There are substantial risks to the successful outcome of the operational and scientific objectives of this expedition. Among these are
In the following sections we will describe the operational sequence to be conducted on this expedition, document some of the known risks and steps we are taking to mitigate them, and present contingency strategies and priorities. Descriptions of coring, downhole, and logging tools are available at www.jamstec.go.jp/chikyu/eng/Expedition/ Operations planAfter departing Shingu (Japan), we will transit for ~1 day to proposed Site NT1-07A and prepare for drilling operations. The operations plan and time estimate are based on formations and depths inferred from seismic and regional geological interpretations without benefit of prior drilling in this area. We have, however, carefully considered information from ODP Legs 190 and 196 (especially Sites 1173, 1174, and 1177, which are located >200 km to the west-southwest). The primary plan for Expedition 322 is to conduct operations in one hole at proposed Site NT1-07A (Fig. F10). The overall operations plan is summarized in Table T1. Proposed Site NT1-07AWe will core one primary hole at proposed Site NT1-07A. The first hole at this site will be cored with the RCB. Coring will start at 400 mbsf and continue to the sediment/basalt interface at 1200 mbsf. If formation conditions permit, we will also attempt pressure measurements within and/or immediately above the unconsolidated sand intervals of the lower Shikoku Basin using the SET-P tool. The hole will be terminated at the sediment/basalt interface but may be continued ~40 m below the sediment/basalt interface. After the hole is conditioned, loaded with mud, and the bit is released in the hole, we will run two wireline logs and a check shot vertical seismic profile (VSP) in open hole. Poor borehole conditions may substantially impact the downhole in situ measurements. A second hole at proposed Site NT1-07A may be cored as a contingency using HPCS/ESCS to refusal or overlap with the top of Hole A. We will conduct formation temperature measurements in the soft mud during HPCS coring (APCT-3) at a target spacing of every third or fourth core and pressure-temperature measurements (SET-P) as permitted by formation conditions. After operations are completed at proposed Site NT1-07A, the ship will be secured for ~1 day transit back to Shingu, Japan. |
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