# US 12,181,626 B2 · Pulsed neutron monitoring of carbon dioxide in reservoirs > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,181,626 B2 - Document ID: US12181626B2 - Status: Granted - Kind: B2 - Application number: 18/153,463 - Filed: 2023-01-12 - Published: 2024-07-18 - Granted: 2024-12-31 - Earliest claimed: 2023-01-12 - Assignees: Weatherford Technology Holdings, LLC - Applicants: Weatherford Technology Holdings, LLC - Inventors: Gregory Schmid - Web page: https://patentgrep.com/patent/US12181626B2 ## CPC - G01V 5/102: {the neutron source being of the pulsed type} - 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 Methods, tools, and systems for determining CO2 saturation in a porous formation using pulsed neutron logging are described. Embodiments of a pulsed neutron logging tool feature a pulsed neutron generator configured to emit pulsed neutrons into the formation and at least two detectors configured to receive emitted photons. The first detector is located closer to the neutron generator than the second detector. Embodiments of the method involve determining first detector formation capture counts indicative of neutron capture photons originating from the formation and detected at the first detector, determining second detector borehole capture counts indicative of neutron capture photons originating from the borehole and detected at the second detector, using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation. ## Claims ### Claim 1 A method of estimating a saturation of carbon dioxide (CO2) in a formation penetrated by a wellbore using a pulsed neutron (PN) tool deployable in the wellbore, wherein the PN tool comprises a source configured to irradiate the formation with fast neutrons, a first detector spaced a first distance from the source, and a second detector spaced a second distance from the source, wherein the second distance is greater than the first distance, and wherein each detector is configured to detect gamma radiation resulting from the irradiating and arriving at the respective detectors, the method comprising: for each of the first and second detectors, receiving neutron capture data indicative of neutron capture photons detected at the respective detectors, determining first detector formation capture counts indicative of neutron capture photons originating from the formation and detected at the first detector, determining second detector borehole capture counts indicative of neutron capture photons originating from the borehole and detected at the second detector, using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation. ### Claim 2 (depends on 1) The method of claim 1, further comprising using the neutron capture data for each of the first and second detectors to determine neutron capture time decay data for each of the detectors. ### Claim 3 (depends on 2) The method of claim 2, wherein: determining the first detector formation capture counts comprises decomposing the neutron capture time decay data for the first detector into a formation contribution and a borehole contribution and disregarding the borehole contribution, and determining the second detector borehole capture counts comprises decomposing the neutron capture time decay data for the second detector into a formation contribution and a borehole contribution and disregarding the formation contribution. ### Claim 4 (depends on 3) The method of claim 3, wherein the decomposing of the neutron capture time decay data for the first and second detectors each comprise fitting the neutron capture time decay data received at the respective detectors to dual exponential functions. ### Claim 5 (depends on 1) The method of claim 1, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation comprises determining a ratio function of the first detector formation capture counts and the second detector borehole capture counts. ### Claim 6 (depends on 5) The method of claim 5, wherein the ratio function comprises a ratio of the first detector formation capture counts to the second detector borehole capture counts. ### Claim 7 (depends on 6) The method of claim 6, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation comprises determining a saturation of a hydrogen containing fluid using the ratio of the first detector formation capture counts to the second detector borehole capture counts. ### Claim 8 (depends on 7) The method of claim 7, wherein the hydrogen containing fluid is one or more of salt water, fresh water, hydrocarbon, and gas. ### Claim 9 (depends on 7) The method of claim 7, wherein determining a saturation of a hydrogen containing fluid comprises calibrating the ratio of the first detector formation capture counts to the second detector borehole capture counts as a function of hydrogen containing fluid saturation using one or more of field data, standard laboratory formation samples, and computer simulations. ### Claim 10 (depends on 7) The method of claim 7, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 comprises estimating the saturation of CO2 using the formula 1 minus hydrogen containing fluid saturation. ### Claim 11 (depends on 1) The method of claim 1, further comprising deploying the PN tool in the wellbore. ### Claim 12 (depends on 11) The method of claim 11, wherein deploying the PN tool in the wellbore comprises conveying the PN tool through the wellbore at a rate of about 2 to about 4 feet per minute. ### Claim 13 (depends on 11) The method of claim 11, wherein deploying the PN tool in the wellbore comprises conveying the PN tool in the wellbore using one or more of a wireline, slickline, coiled tubing and a drill string. ### Claim 14 A system for estimating a saturation of carbon dioxide (CO2) in a formation penetrated by a wellbore using a pulsed neutron (PN) tool deployable in the wellbore, wherein the PN tool comprises a source configured to irradiate the formation with fast neutrons, a first detector spaced a first distance from the source, and a second detector spaced a second distance from the source, wherein the second distance is greater than the first distance, and wherein each detector is configured to detect gamma radiation resulting from the irradiating and arriving at the respective detectors, the system comprising: a non-transitory computer readable storage medium comprising instructions, which when executed by a computer configure the computer to perform a method comprising: for each of the first and second detectors, receiving neutron capture data indicative of neutron capture photons detected at the respective detectors, determining first detector formation capture counts indicative of neutron capture photons originating from the formation and detected at the first detector, determining second detector borehole capture counts indicative of neutron capture photons originating from the borehole and detected at the second detector, using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation. ### Claim 15 (depends on 14) The system of claim 14, wherein the method further comprises: using the neutron capture data for each of the first and second detectors to determine neutron capture time decay data for each of the detectors, determining the first detector formation capture counts comprises decomposing the neutron capture time decay data for the first detector into a formation contribution and a borehole contribution and disregarding the borehole contribution, and determining the second detector borehole capture counts comprises decomposing the neutron capture time decay data for the second detector into a formation contribution and a borehole contribution and disregarding the formation contribution. ### Claim 16 (depends on 14) The system of claim 14, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation comprises determining a ratio function of the first detector formation capture counts and the second detector borehole capture counts. ### Claim 17 (depends on 16) The system of claim 16, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 in the formation comprises determining a saturation of a hydrogen containing fluid using the ratio of the first detector formation capture counts to the second detector borehole capture counts. ### Claim 18 (depends on 17) The system of claim 17, wherein the hydrogen containing fluid is one or more of salt water, fresh water, hydrocarbon, and gas. ### Claim 19 (depends on 17) The system of claim 17, wherein determining a saturation of a hydrogen containing fluid comprises calibrating the ratio of the first detector formation capture counts to the second detector borehole capture counts as a function of hydrogen containing fluid saturation using one or more of field data, standard laboratory formation samples, and computer simulations. ### Claim 20 (depends on 17) The system of claim 17, wherein using the first detector formation capture counts and the second detector borehole capture counts to estimate the saturation of CO2 comprises estimating the saturation of CO2 using the formula 1 minus hydrogen containing fluid saturation.