Description

Applications

Schematic illustration of the Resistivity-at-the-Bit tool (LWD-RAB).

Specifications

ODP Logging Services, Lamont-Doherty Earth Observatory, Rt. 9W, Palisades, NY 10964

Logging-While-DrillingResistivity-at-the-Bit Tool

Detection of resistivity heterogeneity viaazimuthal resistivity images

Lithology estimation Instantaneous detection of casing and coring

points Accurate resistivity when mud is salty or

formation resistivity is high Detection of early invasion of borehole fluids

into the formation

The Resistivity-at-the-Bit tool (LWD-RAB) makesazimuthal resistivity and gamma ray measurements whiledrilling. Using an azimuthal positioning system,measurements are acquired around the borehole to create ahigh resolution, 360-degree resistivity image of the drilledhole. The RAB tool may be connected directly behind thebit or further back in the bottom hole assembly. It may berun with other LWD tools such as the ADN, ISONIC orNMR. Typically, the RAB data are stored in memory withinthe tool and retrieved at the end of the bit run. As an option,the data may be transmitted to a surface acquisition systemif a Measurement-While-Drilling (MWD) power pulse toolis run in conjunction with the RAB.

Assembly of the RAB tool aboardthe JOIDES Resolution.

Optional uphole connector

Batteries

Upper sensor

Middle sensor, containing focused ring electrode

Azimuthal gamma ray

Field-replaceable stabilizer

Lower sensor

Float valve boreRbit electrode

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