| 摘要 |
An MWD method and apparatus for determining parameters of interest in a formation has a sensor assembly mounted on a slidable sleeve slidably coupled to a longitudinal member, such as a section of drill pipe. When the sensor assembly is held in a non-rotating position, for instance for obtaining the measurements, the longitudinal member is tree to rotate an d continue drilling the borehole, wherein downhole measurements can be obtained with substantially n o sensor movement or vibration. This is particularly useful in making NMR measurements due to their susceptibility to errors caused by tool vibration. In addition. the substantially non- rotating arrangement of sensors makes it possible to efficiently cam out VSPs, reverse VSPs and looking ahead of the drill bit. A clamping device is used, for instance, to hold the sensor assembly in the non-rotating position. The sensor assembly of the present invention can include any of a variety of sensors and/or transmitters for determining a plurality of parameters of interest including, for example, nuclear magnetic resonance measurements.
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