Radiant energy – Geological testing or irradiation – Well testing apparatus and methods
Patent
1995-05-22
1997-01-21
Fields, Carolyn E.
Radiant energy
Geological testing or irradiation
Well testing apparatus and methods
250266, G01V 510
Patent
active
055961916
ABSTRACT:
A method of determining porosity of an earth formation penetrated by a wellbore including irradiating the earth formation with bursts of neutrons from a source in the wellbore and counting epithermal neutrons at a first detector axially spaced from the source to be primarily responsive to output of the source. Counting neutrons is divided into buildup periods contemporaneous with the bursts and decay periods between bursts. Neutrons are counted at a second detector during buildup and decay, the second detector axially spaced from the source and radially displaced towards the wellbore to be responsive to epithermal neutrons from the formation and relatively insensitive to lithology. Neutrons are counted at a third detector during burst and decay, the third detector axially spaced from the source and radially displaced towards the wellbore to be primarily responsive to epithermal neutrons from the formation, but the response is partially affected by said lithology. First, second, and third ratios are calculated of counts of the second to first detectors, and third to first detectors, for the burst and decay periods. Porosity is calculated from the third ratio, tool standoff is calculated from the first and said second ratios. In a particular embodiment the first and third ratios can be adjusted for the diameter of the wellbore and fluid salinity by a predetermined relationship and the lithology determined by cross-plotting the adjusted first ratio and adjusted third ratio.
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Fagin Richard A.
Fields Carolyn E.
Glick Edward J.
Western Atlas International Inc.
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