IODP

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doi:10.2204/iodp.sp.340T.2011

Scientific objectives

Two observations will be valuable for ocean lithosphere studies in general, and these must be made with minimum possible disturbance:

  1. Visual observation of whether the well is “producing” (flow out of the hole) or not: addresses fluid flow within the crust and chemical exchange with seawater in maturing lithosphere.

  2. Measurement of temperature throughout the borehole: assesses conditions that may be encountered by future ultradeep drilling/logging of an intrusive oceanic section; tests for possible fluid flow (temperature dips) within fault zones of Atlantis Massif’s footwall.

Focusing on our main objectives, obtaining new caliper measurements throughout the hole is necessary so that we can select VSP station depths where borehole diameter/condition is optimum for instrument coupling. The aim is for station spacing of 25 m throughout the hole, including depths as shallow as ~50 m if hole conditions warrant. The VSP data should increase our knowledge of local reflectivity for near-vertical waves, thereby improving core-log integration. Information on the condition of the borehole is crucial for determining whether a future single-ship, wireline reentry experiment is viable or whether the drillship and a second vessel will be needed to complete the VSP experiment by conducting a walk-away component. Ultimately, this full data set will enable core-log-survey integration at as high a level as possible with current geophysical data.

Sonic logs will be extended to cover the full hole. The upper part of the hole (<800 mbsf) will be relogged, including Stoneley wave measurements, which can provide additional information on permeability/fracturing and any contrast thereof, between lithologic/alteration intervals.

Magnetic susceptibility logs will target downhole variation in magnetite that is a product of serpentinization, so providing constraint on extents/style of alteration that may have been missed with the finite (although very good) core recovery (nonwhite portion of Fig. F3A).

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