Radiant energy – Geological testing or irradiation – Well testing apparatus and methods
Patent
1991-04-04
1991-11-26
Fields, Carolyn E.
Radiant energy
Geological testing or irradiation
Well testing apparatus and methods
250262, 250268, G01V 510
Patent
active
050685317
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. The determined borehole to formation amplitude ratio is used to correct the determined formation decay constant for the effects of detector standoff from the borehole wall. 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 formation decay constant calibrated in borehole models of known porosities.
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Allen L. Scott
Mills William R.
Stromswold Daivd C.
Dunn Drew A.
Fields Carolyn E.
Hager Jr. George W.
McKillop Alexander J.
Mobil Oil Corporation
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