# US 2013/0158876 A1 · Combining inelastic and capture gamma ray spectroscopy for determining formation elemental > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0158876 A1 - Document ID: US20130158876A1 - Status: Published application - Kind: A1 - Application number: 13/656,287 - Filed: 2012-10-19 - Published: 2013-06-20 - Earliest claimed: 2011-12-15 - Assignees: Schlumberger Technology Corporation - Inventors: James A. Grau - Web page: https://patentgrep.com/patent/US20130158876A1 ## CPC - G01V 5/101: {and detecting the secondary Y-rays produced in the surrounding layers of the bore hole} - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract A method for determining weight fractions of a plurality of elements in a subsurface formation penetrated by a wellbore includes determining weight fractions of a first plurality of elements using measurements of capture gamma rays made in the wellbore. The capture gamma rays result from bombardment of the formations with high energy neutrons. A weight fraction of a second plurality of elements is determined using measurements of inelastic gamma rays made in the wellbore resulting from bombardment of the formations with high energy neutrons. The weight fraction for the second plurality is determined by setting a transformation factor for those elements common to both the first and second plurality to result in a statistically equivalent weight fraction for the common elements as determined, for the first plurality of elements. Weight fractions of elements in the second plurality not common to the first plurality of elements is determined using the set transformation factor. ## Claims ### Claim 1 A method for determining weight fractions of a plurality of elements in a subsurface formation penetrated by a wellbore, comprising: in a computer, determining weight fractions of a first plurality of elements using measurements of capture gamma rays made in the wellbore, the capture gamma rays resulting from bombardment of the formations with high energy neutrons; in the computer, determining weight fractions of a second plurality of elements using measurements of inelastic gamma rays made in the wellbore, the inelastic gamma rays resulting from bombardment of the formations with high energy neutrons, the weight fractions of the second plurality determined by setting a transformation factor for those elements common to both the first and second plurality of elements to result in a statistically equivalent determined weight fraction for the common elements as determined for the first plurality of elements; in the computer, determining weight fractions of elements in the second plurality not common to the first plurality of elements using the set transformation factor. ### Claim 2 (depends on 1) The method of claim 1 wherein the determining weight fractions of the first plurality of elements comprises minimization of a closure function. ### Claim 3 (depends on 2) The method of claim 2 wherein determining weight fractions of the first plurality of elements comprises determining enhanced weight fractions thereof and recalculating a transformation factor for the first plurality of elements until differences between the determined weight fractions of the first plurality of elements and the enhanced weight fractions is at least one of minimized and fall below a selected threshold. ### Claim 4 (depends on 1) The method of claim 1 wherein the bombardment of the formation comprises emitting controlled duration bursts of neutrons from a pulsed neutron generator. ### Claim 5 (depends on 4) The method of claim 4 wherein the inelastic gamma rays are detected in a first selected time range during and/or after at least one of the neutron bursts. ### Claim 6 (depends on 4) The method of claim 4 wherein the capture gamma rays are detected in a second selected time range after an end of at least one neutron burst. ### Claim 7 (depends on 1) The method of claim 1 wherein the detecting gamma rays comprises activation thereby of a scintillation detector. ### Claim 8 (depends on 7) The method of claim 7 wherein the determining weight fractions of elements comprises analyzing numbers of gamma rays having particular energy levels by measuring an amplitude of light flashes emanating from the scintillation detector upon detection gamma rays. ### Claim 9 A method for well logging comprising: moving a well logging instrument along a wellbore drilled through subsurface formations, the well logging instrument including a source of high energy neutrons and at least one gamma ray detector, the gamma ray detector coupled to a spectral analyzer; in a computer, determining weight fractions of a first plurality of elements using measurements of capture gamma rays made in the wellbore, the capture gamma rays resulting from bombardment of the formations with high energy neutrons; in the computer, determining weight fractions of a second plurality of elements using measurements of inelastic gamma rays made in the wellbore, the inelastic gamma rays resulting from bombardment of the formations with high energy neutrons, the weight fractions of the second plurality determined by setting a transformation factor for those elements common to both the first and second plurality of elements to result in a statistically equivalent determined weight fraction for the common elements as determined for the first plurality of elements; in the computer, determining weight fractions of elements in the second plurality not common to the first plurality of elements using the set transformation factor. ### Claim 10 (depends on 9) The method of claim 9 wherein the determining weight fractions of the first plurality of elements comprises minimization of a closure function. ### Claim 11 (depends on 10) The method of claim 10 wherein determining weight fractions of the first plurality of elements comprises determining enhanced weight fractions thereof and recalculating a transformation factor for the first plurality of elements until differences between the determined weight fractions of the first plurality of elements and the enhanced weight fractions is at least one of minimized and fall below a selected threshold. ### Claim 12 (depends on 9) The method of claim 9 wherein the moving the well logging instrument along the wellbore drilled through subsurface formations comprises extending and/or retracting an electrical cable having the well logging instrument coupled to an end thereof. ### Claim 13 (depends on 9) The method of claim 9 wherein the moving a well logging instrument along a wellbore drilled through subsurface formations comprises moving a drill string having the well logging instrument forming a part thereof along the wellbore. ### Claim 14 (depends on 9) The method of claim 9 wherein the bombardment of the formation comprises emitting controlled duration bursts of neutrons from a pulsed neutron generator. ### Claim 15 (depends on 14) The method of claim 14 wherein the inelastic gamma rays are detected in a first selected time range during and/or after at least one of the neutron bursts. ### Claim 16 (depends on 14) The method of claim 14 wherein the capture gamma rays are detected in a second selected time range after an end of at least one neutron burst. ### Claim 17 (depends on 9) The method of claim 9 wherein the detecting gamma rays comprises activation thereby of a scintillation detector. ### Claim 18 (depends on 17) The method of claim 17 wherein the determining weight fractions of elements comprises analyzing numbers of gamma rays having particular energy levels by measuring an amplitude of light flashes emanating from the scintillation detector upon detection gamma rays.