Table T7. Measurement performance specification of the geoVISION. Vertical resolution and depth of investigation of geoVISION measurements. (See table notes.)
| Measurement | Vertical resolution (inch) |
Depth of investigation (inch) |
Diameter of investigation (Rt/Rxo) |
Horizontal resolution [(Rt/Rxo = 10) × π]/56 |
Midpoints of extremes |
||
|---|---|---|---|---|---|---|---|
| Rt/Rxo = 10 | Rt/Rxo = 0.1 | Rt/Rxo = 10 | Rt/Rxo = 0.1 | ||||
| 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 |
Notes: * = depends on bit subs. 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. Invasion may be minimal due to measurement of resistivity soon after cutting of hole. Then Rt/Rxo = 1. Resistivity of our drilling fluid, seawater, is 0.19 Ωm. Formation is 0.4 – 0.6 Ωm. (e.g., below frontal thrust in 808) so Rt/Rxo >1 depending on invasion. 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°.
Previous | Close | Top of page