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Mud Resistivity Determination from Multilaterolog Source Impedances

IP.com Disclosure Number: IPCOM000240615D
Publication Date: 2015-Feb-12
Document File: 3 page(s) / 15K

Publishing Venue

The IP.com Prior Art Database

Abstract

The borehole correction for a multilaterolog instrument is sometimes hampered by inaccurate measurements of the mud resistivity Rm by the mud resistivity sonde. We can use the same approach as for the borehole correction to estimate mud resistivity (Rm) from the source impedance measurements, making the service independent of an external mud measurement.

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RES4-54388

Title:

Mud Resistivity Determination from Multilaterolog Source Impedances

Abstract:

The borehole correction for a multilaterolog instrument is sometimes hampered by inaccurate measurements of the mud resistivity Rm by the mud resistivity sonde.  We can use the same approach as for the borehole correction to estimate mud resistivity (Rm) from the source impedance measurements, making the service independent of an external mud measurement.

Description:

The borehole correction for a multilaterolog instrument is sometimes hampered by inaccurate measurements of the mud resistivity Rm by the mud resistivity sonde. Sometimes the Rm sonde is not properly calibrated or it is defective, apart from the fact that the accuracy is not sufficient for very low mud resistivities below 0.1 Ohm-m.

The multilaterolog device measures the source voltages and source currents in addition to the standard focused measurements used for formation evaluation. The source measurements are unfocused and depend mostly on the resistance of the mud column, but there is still some influence from the formation. The guard electrodes involved in the source measurements are quite long, so these measurements have low vertical resolution of about 10ft. This is acceptable, because the mud resistivity does not change rapidly.

The multilaterolog adaptive borehole correction typically uses borehole size from the caliper measurement, mud resistivity (typically from the Rm measurement), and  flushed zone resistivity (Rxo) from the micro-laterolog as a-priori information.  These inputs are combined with the four focused multilaterolog measurements to determine tool eccentricity, flushed zone radius and non-invaded formatio...