Neutron logging method and apparatus for determining a formation characteristic free of environmental effects

Claim 1

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to tool standoff from said borehole wall without explicitly determining said standoff.

Claim 2

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to tool standoff from said borehole wall without explicitly determining said standoff.

Claim 3

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said first and second detector signals, producing a tangible representation of porosity inherently free of tool standoff from said borehole wall without explicitly determining said standoff; and d. generating a tangible representation of said tool standoff determined from said first and second detector signals.

Claim 4

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said first and second detector signals, producing a tangible representation of porosity inherently free of tool standoff from said borehole wall without explicitly determining said standoff; and d. generating a tangible representation of said tool standoff determined from said first and second detector signals.

Claim 6

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. geneating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; d. in response to said first and second signals and to said ideal tool response, producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 7

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. geneating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; d. in response to said first and second signals and to said ideal tool response, producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 8

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; d. predetermining tool response to said formation characteristic in terms of the first detector signal and the second detector signal, as a function of variations in said at least one element of the environment of the investigation; e. in response to said first and second signals, to said predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said ideal tool response, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 9

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; d. predetermining tool response to said formation characteristic in terms of the first detector signal and the second detector signal, as a function of variations in said at least one element of the environment of the investigation; e. in response to said first and second signals, to said predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said ideal tool response, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 10

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool and a caliper through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said caliper, producing a third signal indicative of borehole size; d. in terms of the first detector signal and the second detector signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; e. in response to said first and second signals, to said third signal, and to said plurality of ideal tool responses, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 11

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool and a caliper through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said caliper, producing a third signal indicative of borehole size; d. in terms of the first detector signal and the second detector signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; e. in response to said first and second signals, to said third signal, and to said plurality of ideal tool responses, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 12

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool and a caliper through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said caliper, producing a third signal indicative of borehole size; d. in terms of the first detector signal and the second detector signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; e. for each of a plurality of borehole sizes, predetermining tool response to said formation characteristic in terms of the first detector signal and the second detector signal, as a function of variations in said at least one element of the environment of the investigation; and f. in response to said first, second and third signals, to said plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said plurality of ideal tool responses, generating a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 13

A method for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising the steps of: a. passing a neutron logging tool and a caliper through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances; b. generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; c. in response to said caliper, producing a third signal indicative of borehole size; d. in terms of the first detector signal and the second detector signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; e. for each of a plurality of borehole sizes, predetermining tool response to said formation characteristic in terms of the first detector signal and the second detector signal, as a function of variations in said at least one element of the environment of the investigation; and f. in response to said first, second and third signals, to said plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said plurality of ideal tool responses, generating a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 28

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to the interactions between neutrons and the nuclei of materials in and around said borehole; b. automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to positioning of said detectors relative to said borehole wall without explicitly determining said relative positioning.

Claim 29

A method for determining the porosity of a sub-surface geological formation traversed by a borehole comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to the interactions between neutrons and the nuclei of materials in and around said borehole; b. automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to positioning of said detectors relative to said borehole wall without explicitly determining said relative positioning.

Claim 32

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; and c. in response to said first and second signals and to said ideal tool response, producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 33

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. in terms of the first detector signal and the second detector signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; and c. in response to said first and second signals and to said ideal tool response, producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 34

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. in terms of the first signal and the second signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; c. predetermining tool response to said formation characteristic in terms of said first and second signals, as a function of variations in said at least one element of the environment of the investigation; and d. in response to said first and second signals, to said predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said ideal tool response, producing a signal representative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 35

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. in terms of the first signal and the second signal, predetermining ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic; c. predetermining tool response to said formation characteristic in terms of said first and second signals, as a function of variations in said at least one element of the environment of the investigation; and d. in response to said first and second signals, to said predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said ideal tool response, producing a signal representative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 36

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. producing a third signal indicative of borehole size; c. in terms of the first signal and the second signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; and d. in response to said first and second signals, to said third signal, and to said plurality of ideal tool responses, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 37

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. producing a third signal indicative of borehole size; c. in terms of the first signal and the second signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; and d. in response to said first and second signals, to said third signal, and to said plurality of ideal tool responses, producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 38

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. producing a third signal indicative of borehole size; c. in terms of the first signal and the second signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; d. in terms of the first signal and the second signal and for each of a plurality of borehole sizes, predetermining a plurality of tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation; and e. in response to said first, second and third signals, to said plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said plurality of ideal tool responses, generating a signal representative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 39

A method for determining a characteristic of a sub-surface geological formation corrected for the effects of at least one element of the environment of the investigation of said formation from within a borehole traversing said formation, comprising the steps of: a. deriving first and second signals indicative respectively of the response of first and second spaced detectors positioned in said borehole to interactions between neutrons and the nuclei of materials in and around said borehole; b. producing a third signal indicative of borehole size; c. in terms of the first signal and the second signal, predetermining an ideal tool response unaffected by said at least one element of the environment of the investigation as a function of said formation characteristic for each of a plurality of different borehole sizes; d. in terms of the first signal and the second signal and for each of a plurality of borehole sizes, predetermining a plurality of tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation; and e. in response to said first, second and third signals, to said plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said plurality of ideal tool responses, generating a signal representative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 46

A system for determining the porosity of a sub-surface geological formation traversed by a borehole comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to tool standoff from said borehole wall without explicitly determining said standoff.

Claim 47

A system for determining the porosity of a sub-surface geological formation traversed by a borehole comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for automatically combining said first and second detector signals into a tangible representation of formation porosity inherently free of effects due to tool standoff from said borehole wall without explicitly determining said standoff.

Claim 48

A system for determining the porosity of a sub-surface geological formation traversed by a borehole comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said first and second detector signals, for producing a tangible representation of porosity inherently free of tool standoff from said borehole wall without explicitly determining said standoff; and c. means for generating a tangible representation of said tool standoff determined from said first and second detector signals.

Claim 49

A system for determining the porosity of a sub-surface geological formation traversed by a borehole comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said first and second detector signals, for producing a tangible representation of porosity inherently free of tool standoff from said borehole wall without explicitly determining said standoff; and c. means for generating a tangible representation of said tool standoff determined from said first and second detector signals.

Claim 51

A system for investigating a sub-surface gelogical formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic, said response being unaffected by said at least one element of the environment of the investigation; c. means responsive to said first and second signals and to said stored ideal tool response for producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 52

A system for investigating a sub-surface gelogical formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic, said response being unaffected by said at least one element of the environment of the investigation; c. means responsive to said first and second signals and to said stored ideal tool response for producing a signal indicative of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 53

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic, said response being unaffected by said at least one element of the environment of the investigation and for storing a predetermined tool response to said formation characteristic in terms of the first detector signal and the second detector signal, said tool response being a function of variations in said at least one element of the environment of the investigation; c. means responsive to said first and second signals, to said stored predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said stored ideal tool response, for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 54

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic, said response being unaffected by said at least one element of the environment of the investigation and for storing a predetermined tool response to said formation characteristic in terms of the first detector signal and the second detector signal, said tool response being a function of variations in said at least one element of the environment of the investigation; c. means responsive to said first and second signals, to said stored predetermined tool response to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said stored ideal tool response, for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 55

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool and a caliper adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said caliper for producing a third signal indicative of borehole size; c. means for storing, in terms of the first and second detector signals, a plurality of predetermined ideal tool responses to said formation characteristic, said responses being unaffected by said at least one element of the environment of the investigation; d. means responsive to said first and second signals, to said third signal, and to said plurality of ideal tool responses for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 56

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool and a caliper adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said caliper for producing a third signal indicative of borehole size; c. means for storing, in terms of the first and second detector signals, a plurality of predetermined ideal tool responses to said formation characteristic, said responses being unaffected by said at least one element of the environment of the investigation; d. means responsive to said first and second signals, to said third signal, and to said plurality of ideal tool responses for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 57

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool and a caliper adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said caliper for producing a third signal indicative of borehole size; c. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic for each of a plurality of borehole sizes, said ideal responses being unaffected by said at least one element of the environment of the investigation, and for storing a plurality of predetermined tool responses to said formation characteristic in terms of the first detector signal and the second detector signal, said plurality of tool responses being a function of variations in said at least one element of the environment of the investigation; d. means responsive to said first, said second, and said third signals, to said stored plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said stored plurality of ideal tool responses, for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.

Claim 58

A system for investigating a sub-surface geological formation traversed by a borehole to determine a formation characteristic corrected for the effects of at least one element of the environment of the investigation, comprising: a. a neutron logging tool and a caliper adapted to be passed through said borehole while irradiating said formation with neutrons, said neutron logging tool including a neutron source and first and second detectors spaced from said source by different distances for generating first and second detector signals indicative of interactions between said neutrons and the nuclei of materials in the vicinity of said detectors; b. means responsive to said caliper for producing a third signal indicative of borehole size; c. means for storing, in terms of the first and second detector signals, a predetermined ideal tool response to said formation characteristic for each of a plurality of borehole sizes, said ideal responses being unaffected by said at least one element of the environment of the investigation, and for storing a plurality of predetermined tool responses to said formation characteristic in terms of the first detector signal and the second detector signal, said plurality of tool responses being a function of variations in said at least one element of the environment of the investigation; d. means responsive to said first, said second, and said third signals, to said stored plurality of predetermined tool responses to said formation characteristic as a function of variations in said at least one element of the environment of the investigation, and to said stored plurality of ideal tool responses, for producing a tangible representation of said formation characteristic corrected for the effects of said at least one element of the environment of the investigation.