Radiant energy – Geological testing or irradiation – Well testing apparatus and methods
Patent
1987-01-15
1989-03-21
Howell, Janice A.
Radiant energy
Geological testing or irradiation
Well testing apparatus and methods
250270, 250256, G01V 510
Patent
active
048146102
ABSTRACT:
The present invention comprises a method for determining the transition point between a portion of a curve comprising a statistically single exponential function and another portion of the curve comprising the composite of said exponential function with another function. The method of the present invention is useful in determining which portion of a composite decay curve is statistically equivalent to a single exponential function. The method of the present invention is particularly useful in the oil and gas industry in connection with the rapid and accurate determination of the decay constant of the formation surrounding a borehole. In the method of the present invention, the measured decay function following radiation of the formation with a burst of fast neutrons is integrated in a plurality of contiguous time gates between the end of the neutron burst and the decay to background radiation levels. The decay function is integrated over each of two subsets of contiguous gates whose leading edges are offset by a known time width. A succession of ratios is constructed for a succession of test intervals each defined by two such subsets. Ratios for different test intervals, each successively further in time from the end of the radiation burst, are statistically compared. Statistical compatibility of two successive ratios implies that the decay function is a statistically single exponential over the time spanned by the two test intervals. Once the portion of the decay curve represented by a statistically single exponential function representative of the surrounding formation is determined, the formation decay constant is easily and accurately determined.
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Attali George
Murdoch Bruce T.
Howell Janice A.
Rauchholz William F.
Western Atlas International Inc.
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