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US 10,379,253 B2Granted
Borehole fluid effect correction for pulsed neutron porosity measurements
AssigneeSchlumberger Technology Corporation
InventorsTong Zhou, Sicco Beekman, Timothy M. Quinlan
Life of this patent
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Abstract
A method for determining formation hydrogen index includes using as input to a computer measurements of numbers of burst gamma rays (gamma rays detected during operation of a pulsed neutron source) and numbers of thermal neutron capture gamma rays made at two different axial spacings from the pulsed neutron source. A ratio of the numbers of burst gamma rays and a ratio of the numbers of thermal neutron capture gamma rays is determined. A corrected ratio of the numbers of thermal neutron capture gamma rays using the ratio of numbers of burst gamma rays is determined. The formation hydrogen index is determined from the corrected ratio.
Claims30
A method for determining formation hydrogen index, comprising:
- moving a pulsed neutron well logging instrument along an interior of a wellbore drilled through subsurface formations, the instrument comprising a pulsed neutron source and at least two gamma ray detectors each located at a different axial spacing from the source;
- at a selected time, imparting a selected duration of a burst of high energy neutrons into the subsurface formations;
- measuring a number of gamma rays during the selected duration burst (“burst gamma rays”), said burst gamma rays comprise inelastic gamma rays and non-inelastic gamma rays;
- measuring a number of thermal neutron capture gamma rays at a selected time after the selected duration burst (“thermal neutron capture gamma rays”);
- using as input to a computer measurements of numbers of burst gamma rays and thermal neutron capture gamma rays made at the two different axial spacings from the pulsed neutron source;
- in the computer, determining a ratio of the numbers of burst gamma rays detected at one axial spacing from the source with respect to a different axial spacing from the source and a ratio of the numbers of thermal neutron capture gamma rays detected at the one axial spacing from the source with respect to the different axial spacing from the source;
- in the computer, calculating a corrected ratio of the numbers of thermal neutron capture gamma rays using the ratio of numbers of burst gamma rays;
- and
- determining the formation hydrogen index from the corrected ratio.
6 more elements
A method for well logging, comprising:
- moving a pulsed neutron well logging instrument along an interior of a wellbore drilled through subsurface formations, the instrument comprising a pulsed neutron source and at least two gamma ray detectors each located at a different axial spacing from the source;
- at selected times, imparting selected duration bursts of high energy neutrons into the subsurface formations;
- measuring numbers of gamma rays during the selected duration bursts (“burst gamma rays”), said burst gamma rays comprise inelastic gamma rays and non-inelastic gamma rays;
- measuring numbers of thermal neutron capture gamma rays at selected times after each of the selected duration bursts;
- inputting to a computer the measurements of numbers of burst gamma rays and numbers of thermal neutron capture gamma rays;
- in the computer, determining a ratio of the numbers of burst gamma rays detected at one axial spacing from the source with respect to burst gamma rays detected a different axial spacing from the source and a ratio of the numbers of thermal neutron capture gamma rays detected at the one axial spacing from the source with respect to thermal neutron capture gamma rays detected at the different axial spacing from the source;
- in the computer, calculating a corrected ratio of the numbers of thermal neutron capture gamma rays using the ratio of numbers of burst gamma rays;
- and
- determining the formation hydrogen index from the corrected ratio.
6 more elements
A method for determining formation hydrogen index, comprising:
- moving a pulsed neutron well logging instrument along an interior of a wellbore drilled through subsurface formations, the instrument comprising a pulsed neutron source and a gamma ray detector located at an axial spacing from the pulsed neutron source;
- at a selected time, imparting a selected duration of a burst of high energy neutrons into the subsurface formations;
- measuring a number of gamma rays during the selected duration burst (“burst gamma rays”) by the gamma ray detector located at the axial spacing from the pulsed neutron source, said burst gamma rays comprise inelastic gamma rays and non-inelastic gamma rays;
- measuring a number of thermal neutron capture gamma rays at a selected time after the selected duration burst (“thermal neutron capture gamma rays”) by the gamma ray detector located at the axial spacing from the pulsed neutron source;
- measuring a reference signal indicative of neutron flux;
- using as input to a computer measurements of numbers of burst gamma rays and the thermal neutron gamma rays;
- using as input to a computer the reference signal indicative of neutron flux;
- in the computer, determining a ratio of the number of burst gamma rays and the reference signal and a ratio of the number of thermal neutron gamma rays and the reference signal;
- in the computer, calculating a corrected ratio of the number of thermal neutron capture gamma rays and the reference signal using the ratio of the number of burst gamma rays and the reference signal;
- and
- determining the formation hydrogen index from the corrected ratio.
8 more elements
A method for determining density of fluid in a wellbore, comprising:
- moving a pulsed neutron well logging instrument along an interior of a wellbore drilled through subsurface formations, the instrument comprising a pulsed neutron source and a gamma ray detector located at an axial spacing from the pulsed neutron source;
- at a selected time, imparting a selected duration of a burst of high energy neutrons into the subsurface formations;
- measuring a number of gamma rays during the selected duration burst (“burst gamma rays”) by the gamma ray detector located at the axial spacing from the pulsed neutron source, said burst gamma rays comprise inelastic gamma rays and non-inelastic gamma rays;
- using as input to a computer measurements of numbers of burst gamma rays, and a reference signal indicative of neutron flux;
- in the computer, determining a ratio of the number of burst gamma rays and the reference signal;
- in the computer, calculating a wellbore fluid density using the ratio of the number of burst counts.
3 more elements
Dependencies are inferred from the claim text.