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Table T4. Measurement performance specifications of the geoVISION tool.

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 ray 12 10

Rt = true resistivity of formation. Rxo = resistivity of zone invaded by drilling fluid. Invasion may be minimal due to measurement of resistivity soon after cutting of hole. Then Rt/Rxo = 1. Horizontal resolution for each of tools intermediate between extremes of Rt/Rxo in table above. Imaging tools record 56 times with each revolution of the tool. Accuracy of segment location is ±1°.

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