ABSTRACT

LWD resistivity measurements have been in commercial service since the mid-1980's. Various measurement techniques have been adopted but none has matched the performance of the industry standard wireline induction measurement. Induction tools have excellent (and reasonably constant) depth of investigation, good accuracy in high resistivity reservoirs, and an absence of formation dielectric effects. In contrast, the drill-collar based Wave Propagation instruments require acceptance of significant technical compromises impacting on measurement quality. Until now the implementation of a genuine induction measurement on a LWD platform had not been achieved. The authors describe the specification and design of a new Low-Frequency (20 KHz) Induction Resistivity tool which provides a simple, reliable, and low cost solution to this problem. The instrument design is described, including the requirement to provide for simple and low cost operation and maintenance. This has been achieved by the use of a modular architecture with self contained, readily removable and replaceable (rather than integral) coil array assemblies. Thus providing the ability to easily add the resistivity module to existing MWD assemblies and allowing for easy replacement of critical component parts ? even in remote locations. System design and response modelling are described, demonstrating the superior deep measurement capability expected from an induction tool combined with a vertical response approaching that of higher frequency measurements. The advantages of Induction over existing LWD techniques are discussed. The paper also discusses the azimuthal response of the measurement, offering enhanced potential for geosteering applications. Results from response modelling, logging, and drilling tests in contrasting lithologies at the Catoosa, Oklahoma test site are presented and discussed. Comparisons with modern, high resolution, dual induction wireline measurements are shown. Case studies in various formation and borehole environments are presented, to demonstrate the application and performance of the measurement in a range of conditions. LWD resistivity measurements have been in commercial service since the mid-1980's. Various measurement techniques have been adopted but none has matched the performance of the industry standard wireline induction measurement. Induction tools have excellent (and reasonably constant) depth of investigation, good accuracy in high resistivity reservoirs, and an absence of formation dielectric effects. In contrast, the drill-collar based Wave Propagation instruments require acceptance of significant technical compromises impacting on measurement quality. Until now the implementation of a genuine induction measurement on a LWD platform had not been achieved. The authors describe the specification and design of a new Low-Frequency (20 KHz) Induction Resistivity tool which provides a simple, reliable, and low cost solution to this problem. The instrument design is described, including the requirement to provide for simple and low cost operation and maintenance. This has been achieved by the use of a modular architecture with self contained, readily removable and replaceable (rather than integral) coil array assemblies. Thus providing the ability to easily add the resistivity module to existing MWD assemblies and allowing for easy replacement of critical component parts ? even in remote locations. System design and response modelling are described, demonstrating the superior deep measurement capability expected from an induction tool combined with a vertical response approaching that of higher frequency measurements. The advantages of Induction over existing LWD techniques are discussed. The paper also discusses the azimuthal response of the measurement, offering enhanced potential for geosteering applications. Results from response modelling, logging, and drilling te

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