Methods and apparatus for borehole-corrected spectral analysis of earth formations

Claim 3

The method of claim 1 wherein said partition factor, P R ,E, is determined by combining a first function of the spatial effects of said region R on said gamma rays and a second function of the temporal effects of said region R on said gamma rays.

Claim 4

The method of claim 2 wherein said first function is representative of the spatial dependence of the thermal neutron flux distribution, φ R , within said region R and said second function is representative of the time dependence of the thermal neutron flux distribution, φ R , within said region R.

Claim 5

The method of claim 2 wherein said first function and said second function for each region, R, are combined by multiplying said first and second functions to provide said partition factor, P R ,E, for said region R.

Claim 6

The method of claim 2 wherein the step of determining said first and second functions comprises the prior step of determining a model which decouples the spatial dependence of the thermal neutron flux distribution within each region, R, from the time dependence of the thermal neutron flux with said each region, R, to permit the partition factor P R ,E, for said each region, R, to be expressed as separately determinable spatial and temporal integrals.

Claim 7

The method of claim 1 wherein: said borehole is an open borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, and the earth formation; and a partition factor P R ,E, is determined for each of said three regions, R.

Claim 8

The method of claim 1 wherein: said borehole is a cased borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, the borehole casing, the cement annulus surrounding the casing, and the earth formation; and a partition factor, P R ,E, is determined for each of said five regions, R.

Claim 9

The method of claim 1 further comprising recording said volume fractions as a function of depth within the borehole.

Claim 12

The method of claim 9 wherein said partition factor P R ,E, is determined by combining a first function of the spatial effects of said region R on said gamma rays and a second function of the temporal effects of said region R on said gamma rays.

Claim 13

The method of claim 10 wherein said first function is representative of the spatial dependence of the thermal neutron flux distribution, φ R , within said region R and said second function is representative of the time dependence of the thermal neutron flux distribution, φ R , within said region R.

Claim 14

The method of claim 10 wherein said first function and said second function for each region, R, are combined by multiplying said first and second functions to provide said partition factor, P R ,E, for said region R.

Claim 15

The method of claim 10 wherein the step of determining said first and second functions comprises the prior step of determining a model which decouples the spatial dependence of the thermal neutron flux distribution within each region, R, from the time dependence of the thermal neutron flux with said each region, R, to permit the partition factor, P R ,E, for said each region, R, to be expressed as separately determinable spatial and temporal integrals.

Claim 16

The method of claim 9 wherein: said borehole is an open borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, and the earth formation; and a partition factor P R ,E is determined for each of said three regions, R.

Claim 17

The method of claim 9 wherein: said borehole is a cased borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, the borehole casing, the cement annulus surrounding the casing, and the earth formation; and a partition factor, P R ,E, is determined for each of said five regions, R.

Claim 18

The method of claim 9 further comprising recording said volume fractions as a function of depth within the borehole.

Claim 19

Apparatus for analyzing an earth formation traversed by a borehole, comprising: a logging tool adapted for movement through the borehole; neutron source means in said logging tool for irradiating the borehole/formation environment with pulses of high-energy neutrons; detection means in said logging tool for detecting gamma rays which result from the capture of thermal neutrons by chemical elements of the borehole and formation constituents; means for determining from said detected capture gamma rays elemental gamma ray yields, Y E , indicative of the presence of specific chemical elements, E, in the borehole/formation measurement environment; means for storing sensitivity factors, S E ,M, representative of the efficiency of detecting said chemical elements, E, in predetermined borehole and formation constituents, M; means for deriving for each of predetermined constituent regions, R, in the borehole/formation measurement environment which contains a chemical element, E, of interest a partition factor, P R ,E, which is a function of the spatial and temporal effects of said region on said gamma rays; and means for determining from said elemental gamma ray yields, Y E , said sensitivity factors, S E ,M, and said partition factors, P R ,E, the volume fractions, V M ,R, of said constituents M in said borehole/formation regions R.

Claim 20

Apparatus for analyzing an earth formation traversed by a borehole, comprising: a logging tool adapted for movement through the borehole; neutron source means in said logging tool for irradiating the borehole/formation environment with pulses of high-energy neutrons; detection means in said logging tool for detecting gamma rays which result from the capture of thermal neutrons by chemical elements of the borehole and formation constituents; means for determining from said detected capture gamma rays elemental gamma ray yields, Y E , indicative of the presence of specific chemical elements, E, in the borehole/formation measurement environment; means for storing sensitivity factors, S E ,M, representative of the efficiency of detecting said chemical elements, E, in predetermined borehole and formation constituents, M; means for deriving for each of predetermined constituent regions, R, in the borehole/formation measurement environment which contains a chemical element, E, of interest a partition factor, P R ,E, which is a function of the spatial and temporal effects of said region on said gamma rays; and means for determining from said elemental gamma ray yields, Y E , said sensitivity factors, S E ,M, and said partition factors, P R ,E, the volume fractions, V M ,R, of said constituents M in said borehole/formation regions R.

Claim 21

The apparatus of claim 17 wherein said partition factor, P R ,E, is determined by combining a first function of the spatial effects of said region R on said gamma rays and a second function of the temporal effects of said region R on said gamma rays.

Claim 22

The apparatus of claim 18 wherein said first function is representative of the spatial dependence of the thermal neutron flux distribution, φ R , within said region R and said second function is representative of the time dependence of the thermal neutron flux distribution, φ R , within said region R.

Claim 23

The apparatus of claim 18 wherein said partition-factor determining means comprises means for multiplying said first and second functions for each region, R, to provide said partition factor, P R ,E, for said region R.

Claim 24

The apparatus of claim 17 wherein: said borehole is an open borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, and the earth formation; and a partition factor P R ,E is determined for each of said three regions, R.

Claim 25

The apparatus of claim 17 wherein: said borehole is a cased borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, the borehole casing, the cement annulus surrounding the casing, and the earth formation; and a partition factor, P R ,E, is determined for each of said five regions, R.

Claim 26

The apparatus of claim 17 further comprising means for recording said volume fractions as a function of depth within the borehole.

Claim 27

Apparatus for analyzing an earth formation traversed by a borehole from thermal neutron capture gamma rays detected within a borehole traversing the formation, comprising: means for determining from said detected gamma rays elemental gamma ray yields, Y E , indicative of the presence of specific chemical elements, E, in the borehole/formation measurement environment; means for storing sensitivity factors, S E ,M, representative of the efficiency of detecting said chemical elements, E, in predetermined borehole and formation constituents, M; means for deriving for each of predetermined constituent regions, R, in the borehole/formation measurement environment which contains a chemical element, E, of interest a partition factor, P R ,E, which is a function of the spatial and temporal effects of said region on said gamma rays; and means for determining from said elemental gamma ray yields, Y E , said sensitivity factors, S E ,M, and said partition factors, P R ,E, the volume fractions, V M ,R, of said constituents M in said borehole/formation regions R.

Claim 28

Apparatus for analyzing an earth formation traversed by a borehole from thermal neutron capture gamma rays detected within a borehole traversing the formation, comprising: means for determining from said detected gamma rays elemental gamma ray yields, Y E , indicative of the presence of specific chemical elements, E, in the borehole/formation measurement environment; means for storing sensitivity factors, S E ,M, representative of the efficiency of detecting said chemical elements, E, in predetermined borehole and formation constituents, M; means for deriving for each of predetermined constituent regions, R, in the borehole/formation measurement environment which contains a chemical element, E, of interest a partition factor, P R ,E, which is a function of the spatial and temporal effects of said region on said gamma rays; and means for determining from said elemental gamma ray yields, Y E , said sensitivity factors, S E ,M, and said partition factors, P R ,E, the volume fractions, V M ,R, of said constituents M in said borehole/formation regions R.

Claim 29

The apparatus of claim 24 wherein said partition factor, P R ,E, is determined by combining a first function of the spatial effects of said region R on said gamma rays and a second function of the temporal effects of said region R on said gamma rays.

Claim 30

The apparatus of claim 25 wherein said first function is representative of the spatial dependence of the thermal neutron flux distribution, φ R , within said region R and said second function is representative of the time dependence of the thermal neutron flux distribution, φ R , within said region R.

Claim 31

The apparatus of claim 25 wherein said partition factor determining means comprises means for multiplying said first and second functions for each region, R, to provide said partition factor, P R ,E, for said region R.

Claim 32

The apparatus of claim 24 wherein: said borehole is an open borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresppnding to each of the logging tool, the borehole fluid, and the earth formation; and a partition factor P R ,E is determined for each of said three regions, R.

Claim 33

The apparatus of claim 24 wherein: said borehole is a cased borehole; and said borehole/formation measurement environment is assumed to comprise a constituent region, R, corresponding to each of the logging tool, the borehole fluid, the borehole casing, the cement annulus surrounding the casing, and the earth formation; and a partition factor, P R ,E, is determined for each of said five regions, R.

Claim 34

The apparatus of claim 24 further comprising means for recording said volume fractions as a function of depth within the borehole.