Borehole imaging and standoff determination using neutron...

Radiant energy – Geological testing or irradiation – Well testing apparatus and methods

Reexamination Certificate

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Reexamination Certificate

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07544929

ABSTRACT:
Apparatus and methods for determining borehole diameter and standoff for neutron porosity logging systems. The apparatus comprises an isotopic neutron source, a single epithermal neutron detector and two thermal neutron detectors, where all detectors are at different axial spacings from the neutron source. Thermal neutron porosity is determined from the combined response of the thermal neutron detectors. Epithermal neutron porosity is determined from the response of the single epithermal neutron detector. Embodied as a wireline system, a difference between thermal neutron porosity and epithermal neutron porosity is used to compute a tool standoff, which in turn is used to correct the thermal neutron porosity for effects of standoff. Borehole size measurements are made independently and preferably with a mechanical caliper of a density tool subsection. Embodied as a LWD system, the difference between thermal neutron porosity and epithermal neutron porosity is used to correct the thermal neutron porosity measurement for both borehole diameter and radial position (standoff) of the tool within the borehole.

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Arnold, “Experimental Determination of Environmental Corrections for a Dual-Spaced Neutron Porosity Log” SPWLA 22nd Annual Logging Symposium, (24 pages) Jun. 23-26, 1981.

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