Radiant energy – Geological testing or irradiation – Well testing apparatus and methods
Patent
1991-07-24
1994-09-06
Dzierzynski, Paul M.
Radiant energy
Geological testing or irradiation
Well testing apparatus and methods
250262, 364422, 395929, G01V 510
Patent
active
053450779
ABSTRACT:
A borehole logging tool is lowered into a borehole traversing a subsurface formation and a neutron detector measures the die-away of nuclear radiation in the formation. A model of the die-away of nuclear radiation is produced using exponential terms varying as the sum of borehole, formation and thermal neutron background components. Exponentially weighted moments of both the die-away measurements and die-away model are determined and equated. The equated moments are solved for the ratio of the borehole to formation amplitude components of the measurements. The formation decay constant is determined from at least the formation and thermal neutron background terms of the weighted measurement and model moments. An epithermal neutron lifetime is determined from the formation decay constant. This epithermal neutron lifetime and the amplitude ratio are used by a trained neural network to determine a lifetime correction and an apparent standoff. A standoff corrected lifetime is determined from the epithermal neutron lifetime and the lifetime correction. A porosity log of the formation is produced which is corrected for detector standoff from the borehole wall as a function of the standoff corrected epithermal neutron lifetime calibrated in borehole models of known porosities.
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Allen L. Scott
Leland Frank P.
Lyle, Jr. W. D.
Stromswold David C.
Bruce David V.
Dzierzynski Paul M.
Hager Jr. George W.
McKillop Alexander J.
Mobil Oil Corporation
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