Recharacterization and Validation of Through-the-Bit-Logging Tool Measurements
- Robin Slocombe (Schlumberger) | Sachin Bammi (Schlumberger) | John Hunka (Schlumberger) | Richard Reischman (Schlumberger) | Gregory Schmid (Schlumberger)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- February 2015
- Document Type
- Journal Paper
- 58 - 71
- 2015. Society of Petrophysicists & Well Log Analysts
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- 192 since 2007
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The need to reliably access tortuous, highly deviated, and restricted wellbores led to the development of a through-the-bit logging system approximately seven years ago. The through-the-bit logging system consists of a full quad-combo, including formation-density, compensated-neutron, induction-resistivity, and array-sonic logging tools, that allows measurements to be made in wellbores where conventional wireline-conveyed logging is not an option. Following the successful deployment of the technology and the commercial acquisition of ThruBit by Schlumberger in 2011, a comprehensive review was made of the measurements in order to make the best use of the combination of a unique conveyance system and over 80 years of downhole sensor and measurement experience. The density, neutron porosity, resistivity, and gammaray measurements were reviewed individually. In some cases, adjustments were required to allow for changes in radioactive-source designs or to be able to use pre-existing calibration facilities. The calibration process, measurement algorithms, and borehole corrections were reviewed. Finally, validation of the measurements under known conditions and comparison with industry benchmark tool responses was performed. The through-the-bit quad-combo logging suite performs at the level of measurement quality required by operators to make confident decisions. This paper addresses the formation gamma-ray, formation-density, compensated-neutron, and induction-resistivity tools.
The ThruBit* through-the-bit logging system was developed with a 2-1/8-in. (54 mm) diameter architecture to allow it to pass through the center of most drillstrings and into the open borehole through a Portal* pass-through bit (Reischman, 2011). This has enabled operators to obtain a full suite of openhole wireline-log measurements in holes that would otherwise have been inaccessible due to small size, restrictions, or geometry. After Schlumberger acquired the through-the-bit logging system, worldwide deployment required that the assets be calibrated using standard inhouse equipment and field acquisition systems. This paper documents how that was accomplished and validated.*Mark of Schlumberger.
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