Techniques for Determining Carbon to Oxygen Ratio Using Neutron-Induced Gamma Ray Spectroscopy
AssigneeWeatherford Technology Holdings, LLC
InventorPaul Baturin
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Abstract
Methods and systems for determining a carbon-to-oxygen (C/O) ratio within a formation are described. The methods and systems use a pulsed neutron tool conveyed within a borehole in the formation to measure gamma rays induced by inelastic scattering events between pulsed neutrons and elements within the formation. The resulting inelastic scattering spectra are treated to remove baseline counts arising from interactions occurring within scintillation materials of the detector and are then deconvolved using elemental standard spectra that are similarly detrended to remove baseline contributions.
Claims20
A method of determining a ratio of at least two elements in a formation traversed by a wellbore, the method comprising:
- conveying a pulsed neutron tool within the wellbore, wherein the pulsed neutron tool comprises a pulsed neutron generator (PNG) and a gamma radiation detector;
- using the PNG to irradiate the formation with pulsed neutrons;
- using the gamma radiation detector to detect gamma rays emitted as a result of interactions of the pulsed neutrons with elements within the formation;
- using the detected gamma rays to generate an inelastic scattering spectrum, wherein the inelastic scattering spectrum comprises:
- peaks indicative of gamma rays arising from inelastic scattering interactions between the pulsed neutrons and the at least two elements, and
- a background signal;
- removing the background signal from the inelastic scattering spectrum to yield a background-corrected inelastic spectrum;
- deconvolving the background-corrected inelastic spectrum to yield concentrations of the at least two elements;
- and
- determining the ratio of the at least two elements.
A system for determining a ratio of at least two elements in a formation traversed by a wellbore, the system comprising:
- a pulsed neutron generator (PNG) configured to irradiate the formation with pulsed neutrons;
- a gamma radiation detector configured to detect gamma rays emitted from the formation as a result of interactions of the pulsed neutrons with elements within the formation;
- a computing device configured to:
- receive data indicative of the detected gamma rays,
- use the data to generate an inelastic scattering spectrum, wherein the inelastic scattering spectrum comprises:
- peaks indicative of gamma rays arising from inelastic scattering interactions between the pulsed neutrons and the at least two elements, and
- a background signal,
- remove the background signal from the inelastic scattering spectrum to yield a background-corrected inelastic spectrum,
- deconvolve the background-corrected inelastic spectrum to yield concentrations of the at least two elements, and
- determine the ratio of the at least two elements.
Dependencies are inferred from the claim text.