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Table T5. Measurement performance specifications of the geoVISION, Expedition 343.

Measurement
Vertical
resolution
(inch)
Depth of investigation (inch)
Diameter of investigation (inch) Horizontal resolution
(inch)
Midpoints of
extremes
(inch)
Rt/Rxo = 10
Rt/Rxo = 0.1
Rt/Rxo = (10 × π)/56
Rt/Rxo = (0.1 × π)/56
Resistivity at the bit 12–24* 12 32 32      
Ring resistivity 2–3 7 22 25      
Button resistivity              
Shallow focused 2–3 1 19 24 1.07 1.35 1.2
Medium focused 2–3 3 15 21 0.84 1.18 1
Deep focused 2–3 5 11 16 0.62 0.9 0.75
Gamma radiation 12 10

* = depends on bit subs. Vertical penetration rate: m/h = 30, inches/h = 1371.6, inches/min = 22.86. At a penetration rate of 30 m/h and typical rotation rate (e.g., 50 rpm) we are oversampling vertically. Rt = true resistivity of formation, Rxo = resistivity of zone invaded by drilling fluid. If invasion is minimal because of measuring resistivity soon after cutting of hole, then Rt/Rxo = 1. Resistivity of our drilling fluid, seawater, is 0.19 Ωm. Formation resistivity is ~0.4–0.6 Ωm. Horizontal resolution for each of tools intermediate between extremes of Rt/Rxo in table above. Imaging tools record 56 times with each revolution of tool. Accuracy of segment location is ±1°.

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