Hydrocarbon detection utilizing neutron borehole measurements

Claim 2

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) operating a neutron source for a predetermined time period; (b) operating a plurality of detectors differently spaced from said source to produce neutron-dependent responses during predetermined times relative to the operation of said source; (c) combining at least some of said responses to produce a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation adjacent said detectors; (d) combining at least some of said responses to produce a function representative of a thermal neutron absorption characteristic of said formation; and (e) combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of said formation to produce a second pore volume indication which is uncompensated for differences between the thermal neutron absorption characteristics of the matrix and any hydrocarbons present in the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 3

The method of claim 1 and further including the step of displaying said produced first and second pore volume indications in a comparable manner.

Claim 4

The method of claim 1 wherein said predetermined time periods are adjusted as a function of said thermal neutron absorption characteristic of said formation.

Claim 5

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which is uncompensated for the thermal neutron absorption characteristic of at least one component of the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 6

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which is uncompensated for the thermal neutron absorption characteristic of at least one component of the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 7

The method of claim 4 and further including the step of displaying said produced first and second pore volume indications in a comparable manner.

Claim 8

The method of claim 5 wherein said first pore volume indication is derived from measurements substantially compensated for any thermal neutron absorption effects of the formation.

Claim 9

The method of claim 6 wherein said measurements are obtained from at least two detectors located at different spacings from a neutron source and are representative of the neutron populations in the formation adjacent to said detectors.

Claim 10

The method of claim 7 wherein the detectors used to obtain the measurements from which the first pore volume indicator is derived are substantially responsive to only epithermal neutron populations and therefore to the slowing down of high energy neutrons by the hydrogen in the formation and substantially unresponsive to thermal neutron absorption characteristics of said formation and borehole.

Claim 11

The method of claim 7 wherein said neutron source is pulsed and said detectors are gated relative to said pulse to begin the measurements after a substantial portion of the neutron population of said borehole adjacent to said detectors has decayed thereby minimizing borehole effects in their measurements, said detectors also gated relative to said pulse to perform the measurements before a substantial portion of the neutron population in the formation adjacent said detectors has decayed below detection levels.

Claim 12

The method of claim 9 wherein the gating of the detectors is dependent upon a decay time measurement at one of said detectors.

Claim 13

The method of claim 10 wherein said decay time measurement is utilized to compensate said first pore volume indication for thermal neutron absorption effects of said formation.

Claim 14

The method of claim 11 wherein said decay time measurement corresponds to said function representative of a thermal neutron absorption characteristic of said formation.

Claim 15

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a measurement which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; (c) combining the absorption characteristic function with the hydrogen-dependent measurement to provide apparent absorption characteristics for the water component of said formation; and (d) combining the absorption characteristic function with other characteristics of the formation to provide a function for recognizing the proper formation for determining a representative absorption characteristic for the water component of said function.

Claim 16

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a measurement which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; (c) combining the absorption characteristic function with the hydrogen-dependent measurement to provide apparent absorption characteristics for the water component of said formation; and (d) combining the absorption characteristic function with other characteristics of the formation to provide a function for recognizing the proper formation for determining a representative absorption characteristic for the water component of said function.

Claim 17

The method of claim 13 and further including combining the representative absorption characteristic for the water component of the formation determined in the proper formation with the function representative of the absorption characteristic of subsurface earth formations to produce a second pore volume indication which is uncompensated for differences in the thermal neutron absorption characteristics of hydrocarbons present in the pore space of the formations such that the pressure of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 18

The method of claim 14 and further including the step of displaying said produced first and second pore volume indications in a comparable manner.

Claim 19

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; producing a function representative of a thermal neutron absorption characteristic of said formation; and combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which assumes there are no substantial differences between the thermal neutron absorption characteristics of the formation matrix and any hydrocarbons present in the pore space in the formation such that the presence of hydrocarbons with thermal neutron absorption characteristics different from the matrix is indicated by differences between said produced first and second pore volume indications.

Claim 20

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; producing a function representative of a thermal neutron absorption characteristic of said formation; and combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which assumes there are no substantial differences between the thermal neutron absorption characteristics of the formation matrix and any hydrocarbons present in the pore space in the formation such that the presence of hydrocarbons with thermal neutron absorption characteristics different from the matrix is indicated by differences between said produced first and second pore volume indications.

Claim 21

The method of claim 16 and further including the step of compensating the second pore volume indication as a function of the thermal neutron absorption characteristic of the hydrocarbon present as indicated by the difference between said first and second pore volume indications.

Claim 22

The method of claim 17 and further including the steps of producing a third pore volume indication representative of the total porosity and combining said produced pore volume indications to produce an indication of the thermal neutron absorption characteristic for the hydrocarbon which is related to the viscosity and thereby producibility of the hydrocarbon as present in the formation.

Claim 23

The method of claim 18 and further including the step of compensating the second pore volume indication as a function of the produced indications of the thermal neutron absorption characteristic for the hydrocarbon present in the formation.

Claim 24

The method of claim 19 wherein said compensation of the second pore volume indication includes compensation for differences between the thermal neutron absorption characteristics of the formation water and the clays present in the formation.

Claim 25

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: means for producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; means for producing a function representative of a thermal neutron absorption characteristic of said formation; and means for combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which is uncompensated for differences between the thermal neutron absorption characteristics of the matrix and any hydrocarbons present in the pore space in the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 26

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: means for producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; means for producing a function representative of a thermal neutron absorption characteristic of said formation; and means for combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication which is uncompensated for differences between the thermal neutron absorption characteristics of the matrix and any hydrocarbons present in the pore space in the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 27

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: means for operating a neutron source for a predetermined time period; means for operating a plurality of detectors differently spaced from said source to produce neutron-dependent responses during predetermined times relative to the operation of said source; means for combining at least some of said responses to produce a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation adjacent to said detectors; means for combining at least some of said responses to produce a function representative of a thermal neutron absorption characteristic of said formation; and means for combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of said formation to produce a second pore volume indication which is uncompensated for differences between the thermal neutron absorption characteristics of the matrix and any hydrocarbons present in the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 28

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: means for operating a neutron source for a predetermined time period; means for operating a plurality of detectors differently spaced from said source to produce neutron-dependent responses during predetermined times relative to the operation of said source; means for combining at least some of said responses to produce a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation adjacent to said detectors; means for combining at least some of said responses to produce a function representative of a thermal neutron absorption characteristic of said formation; and means for combining the absorption characteristic function of said formation with a predetermined absorption characteristic for the water component of said formation to produce a second pore volume indication which is uncompensated for differences between the thermal neutron absorption characteristics of the matrix and any hydrocarbons present in the formation such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 29

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) combining the absorption characteristic function of said formation with the first pore volume indication and a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 30

A machine method of automatically indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) combining the absorption characteristic function of said formation with the first pore volume indication and a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 31

The method of claim 23 and further including the step of displaying said produced first and second pore volume indications in a comparable manner.

Claim 32

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) means for producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) means for producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) means for combining the absorption characteristic function of said formation with the first pore volume indication and a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 33

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) means for producing a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation; (b) means for producing a function representative of a thermal neutron absorption characteristic of said formation; and (c) means for combining the absorption characteristic function of said formation with the first pore volume indication and a predetermined absorption characteristic for the water component of the formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 34

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) means for operating a neutron source for a predetermined time period; (b) means for operating a plurality of detectors differently spaced from said source to produce neutron-dependent responses during predetermined times relative to the operation of said source; (c) means for combining at least some of said responses to produce a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation adjacent to said detectors; (d) means for combining at least some of said responses to produce a function representative of a thermal neutron absorption characteristic of said formation; and (e) means for combining the absorption characteristic function of said formation with said produced first pore volume indication and a predetermined absorption characteristic for the water component of said formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.

Claim 35

Apparatus for indicating the presence of hydrocarbons in subsurface earth formations traversed by a borehole, comprising: (a) means for operating a neutron source for a predetermined time period; (b) means for operating a plurality of detectors differently spaced from said source to produce neutron-dependent responses during predetermined times relative to the operation of said source; (c) means for combining at least some of said responses to produce a first pore volume indication which is primarily dependent upon the hydrogen content of the fluid in the pore space of a formation adjacent to said detectors; (d) means for combining at least some of said responses to produce a function representative of a thermal neutron absorption characteristic of said formation; and (e) means for combining the absorption characteristic function of said formation with said produced first pore volume indication and a predetermined absorption characteristic for the water component of said formation to produce a second pore volume indication such that the presence of hydrocarbons is indicated by differences between said produced first and second pore volume indications.