Logging technique for assaying for uranium in rock formations

Claim 2

In a method of assaying for uranium ore in natural earth formations traversed by a borehole, the steps comprising: a. irradiating a formation of interest with a source of fast neutrons whereby neutrons from said source are moderated in said formation to lower energy levels and are subject to absorption, b. detecting secondary radiation attendant to said lower energy neutrons originating from said source at a time when said lower energy neutrons exist in said formation, c. recording the count rate of radiation detected in step (b) to obtain a log representative of the response of said formation to moderation and absorption of neutrons, d. irradiating said formation with repetitive bursts of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect radiation attendant to delayed neutrons resulting from neutron fission of uranium, f. recording radiation detected in step (e) to obtain a log representative of uranium content in said formation, and g. correlating the logs obtained in steps (c) and (f) to determine a corrected value of uranium content in said formation.

Claim 3

The method of claim 1 wherein the radiation detected in step (b) comprises neutrons from said lower energy neutron population.

Claim 4

The method of claim 2 wherein the neutrons detected in step (b) comprise thermal neutrons.

Claim 5

The method of claim 1 wherein the radiation detected in step (e) comprises thermal neutrons.

Claim 6

The method of claim 1 wherein the source employed in step (a) is of a substantially, constant neutron intensity.

Claim 7

The method of claim 1 wherein the irradiation in step (a) is carried out with a continuous source of fast neutrons.

Claim 8

The method of claim 1 further comprising the steps of: h. concomitantly with step (d) operating a detector separate from the detector of step (e) to detect delayed radiation resulting from irradiation of a designated element with said bursts of fast neutrons, i. recording radiation detected in step (h) to obtain a representation of the quantity of neutrons produced in said bursts.

Claim 9

The method of claim 7 wherein the radiation detected in step (h) comprises gamma rays emitted from oxygen in accordance with the reaction: 016(n,p)N16 -> 016 + gamma .

Claim 10

In a method of assaying for uranium ore in natural earth formations traversed by a borehole, the steps comprising: a. irradiating a formation of interest with a source of fast neutrons whereby said fast neutrons are moderated in said formation to form a thermal neutron population subject to absorption within said formation, b. detecting thermal neutrons from said thermal neutron population, c. recording the count rate of thermal neutrons detected in step (b) to obtain a log representative of the response of said formation to moderation and absorption of neutrons, d. irradiating said formation with repetition bursts of fast neutrons from another source of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect delayed thermal neutrons resulting from neutron fission of uranium, f. recording delayed neutrons detected in step (e) to obtaiN a log representative of uranium content in said formation, and g. correlating the logs obtained in steps (c) and (f) to determine a corrected value of uranium content in said formation.

Claim 11

In a method of assaying for uranium ore in natural earth formations traversed by a borehole, the steps comprising: a. irradiating a formation of interest with a source of fast neutrons whereby said fast neutrons are moderated in said formation to form a thermal neutron population subject to absorption within said formation, b. detecting thermal neutrons from said thermal neutron population, c. recording the count rate of thermal neutrons detected in step (b) to obtain a log representative of the response of said formation to moderation and absorption of neutrons, d. irradiating said formation with repetition bursts of fast neutrons from another source of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect delayed thermal neutrons resulting from neutron fission of uranium, f. recording delayed neutrons detected in step (e) to obtaiN a log representative of uranium content in said formation, and g. correlating the logs obtained in steps (c) and (f) to determine a corrected value of uranium content in said formation.

Claim 12

The method of claim 9 further comprising the steps of: h. concomitantly with step (d) operating a detector separate from the detector of step (e) to detect delayed radiation resulting from irradiation of a designated element with said bursts of fast neutrons, i. recording radiation detected in step (h) to obtain a representation of the quantity of neutrons produced in said bursts.

Claim 13

The method of claim 10 wherein the radiation detected in step (h) comprises gamma rays emitted from oxygen in accordance with the reaction: 016(n,p)N16 -> 016 + gamma .

Claim 14

The method of claim 9 wherein said corrected value of uranium content is determined by comparing the log obtained in step (c) with a suite of calibration functions defining the relationships between the quantity of delayed neutrons detected and the concentration of uranium for different values of moderation and absorption of neutrons, selecting a calibration function which corresponds to the response value indicated by the log of step (c), and comparing the log of step (f) with said selected calibration function to determine said corrected value of uranium content.

Claim 15

The method of claim 9 wherein the source employed in step (a) is of a substantially constant neutron intensity.

Claim 16

The method of claim 13 wherein the irradiation in step (a) is carried out with a continuous source of fast neutrons.

Claim 17

In the development of criteria for use in correcting a uranium assay log of the type obtained by irradiating a natural earth formation with fast neutrons and detecting radiation attendant to delayed neutrons resulting from neutron fission of uranium, the method comprising: a. irradiating a formation with fast neutrons whereby said fast neutrons are moderated in said formation to lower energy levels and are subject to absorption, b. detecting secondary radiation attendant to said lower energy neutrons, c. recording radiation detected in step (b) to obtain a log representative of at least one response factor of said formation to said neutrons, d. in a first set of a plurality of formations having a response factor substantially the same as that recited in step (c) and having different known uranium concentrations, irradiating each of said formations with repetitive bursts of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. for each of the formations recited in step (d) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect radiation attendant to delayed neutrons resulting from neutron fission of uranium, f. recording radiation detected in step (e) to obtain a log of radiation as a function of uranium concentration, g. in a second set of a plurality of formations having a substantially constant concentration of an element which responds to irradiation with fast neutrons to emit delayed neutrons and in which said response factor varies quantitatively, irradiating each of said formations with fast neutrons whereby said fast neutrons are moderated therein to lower energy levels, and are subject to absorption, h. for each of the formations recited in step (g) detecting radiation attendant to said lower energy neutrons, i. irradiating each of the formations recited in step (g) with repetitive bursts of fast neutrons, j. for each of the formations in step (g) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts detecting radiation attendant to delayed neutrons emitted by said element, k. recording the radiation detected in step (h) as a function of the radiation detected in step (j), l. correlating the function of step (k) with the log of step (c) to develop normalization factors for a plurality of values of said response factor, and m. applying said normalization factors to the log of step (f) to develop a suite of calibration functions for different values of said response factor.

Claim 18

In the development of criteria for use in correcting a uranium assay log of the type obtained by irradiating a natural earth formation with fast neutrons and detecting radiation attendant to delayed neutrons resulting from neutron fission of uranium, the method comprising: a. irradiating a formation with fast neutrons whereby said fast neutrons are moderated in said formation to lower energy levels and are subject to absorption, b. detecting secondary radiation attendant to said lower energy neutrons, c. recording radiation detected in step (b) to obtain a log representative of at least one response factor of said formation to said neutrons, d. in a first set of a plurality of formations having a response factor substantially the same as that recited in step (c) and having different known uranium concentrations, irradiating each of said formations with repetitive bursts of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. for each of the formations recited in step (d) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect radiation attendant to delayed neutrons resulting from neutron fission of uranium, f. recording radiation detected in step (e) to obtain a log of radiation as a function of uranium concentration, g. in a second set of a plurality of formations having a substantially constant concentration of an element which responds to irradiation with fast neutrons to emit delayed neutrons and in which said response factor varies quantitatively, irradiating each of said formations with fast neutrons whereby said fast neutrons are moderated therein to lower energy levels, and are subject to absorption, h. for each of the formations recited in step (g) detecting radiation attendant to said lower energy neutrons, i. irradiating each of the formations recited in step (g) with repetitive bursts of fast neutrons, j. for each of the formations in step (g) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts detecting radiation attendant to delayed neutrons emitted by said element, k. recording the radiation detected in step (h) as a function of the radiation detected in step (j), l. correlating the function of step (k) with the log of step (c) to develop normalization factors for a plurality of values of said response factor, and m. applying said normalization factors to the log of step (f) to develop a suite of calibration functions for different values of said response factor.

Claim 19

In the development of criteria for use in correcting a uranium assay log of the type obtained by irradiating a natural earth formation with fast neutrons and detecting radiation attendant to delayed neutrons resulting from neutron fission of uranium, the method comprising: a. irradiating a formation with fast neutrons whereby said fast neutrons are moderated in said formation to form a thermal neutron population, b. detecting thermal neutrons from said thermal neutron population, c. recording radiation detected in step (b) to obtain a log representative of a response factor of said formation to moderation and absorption of neutrons, d. in a first set of a plurality of formations having a response factor substantially the same as that recited in step (c) and having different known uranium concentrations, irradiating each of said formations with repetitive bursts of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. for each of the formations recited in step (d) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect delayed neutrons resulting from neutron fission of uranium, f. recording the quantity of neutrons detected in step (e) to obtain a log of delayed neutron counts as a function of uranium concentration, g. in a second set of a plurality of naturally occurring earth formations having a substantially constant oxygen concentration and different response factors for moderation and absorption of neutrons, irradiating each of said formations with fast neutrons whereby said fast neutrons are moderated therein to form a thermal neutron population, h. for each of the formations recited in step (g) detecting thermal neutrons from said thermal neutron population, i. irradiating each of the formations recited in step (g) with repetitive bursts of fast neutrons, j. for each of the formations in step (g) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts detecting delayed neutrons emitted by oxygen, k. recording the radiation detected in step (h) as a function of the radiation detected in step (j), l. correlating the function obtained by step (k) with the log of step (c) to develop normalization factors for a plurality of values of said response factor, and m. applying said normalization factors to the log of step (f) to develop a suite of calibration functions for different values of said response factor.

Claim 20

In the development of criteria for use in correcting a uranium assay log of the type obtained by irradiating a natural earth formation with fast neutrons and detecting radiation attendant to delayed neutrons resulting from neutron fission of uranium, the method comprising: a. irradiating a formation with fast neutrons whereby said fast neutrons are moderated in said formation to form a thermal neutron population, b. detecting thermal neutrons from said thermal neutron population, c. recording radiation detected in step (b) to obtain a log representative of a response factor of said formation to moderation and absorption of neutrons, d. in a first set of a plurality of formations having a response factor substantially the same as that recited in step (c) and having different known uranium concentrations, irradiating each of said formations with repetitive bursts of fast neutrons, the time intervals between said bursts being greater than the time required for dissipation of neutrons originating in said bursts, e. for each of the formations recited in step (d) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts operating a detector to detect delayed neutrons resulting from neutron fission of uranium, f. recording the quantity of neutrons detected in step (e) to obtain a log of delayed neutron counts as a function of uranium concentration, g. in a second set of a plurality of naturally occurring earth formations having a substantially constant oxygen concentration and different response factors for moderation and absorption of neutrons, irradiating each of said formations with fast neutrons whereby said fast neutrons are moderated therein to form a thermal neutron population, h. for each of the formations recited in step (g) detecting thermal neutrons from said thermal neutron population, i. irradiating each of the formations recited in step (g) with repetitive bursts of fast neutrons, j. for each of the formations in step (g) and during time intervals between said bursts and after dissipation of neutrons originating in said bursts detecting delayed neutrons emitted by oxygen, k. recording the radiation detected in step (h) as a function of the radiation detected in step (j), l. correlating the function obtained by step (k) with the log of step (c) to develop normalization factors for a plurality of values of said response factor, and m. applying said normalization factors to the log of step (f) to develop a suite of calibration functions for different values of said response factor.