Combination of epithermal and inelastic neutron scattering methods to locate coal and oil shale zones
AssigneeTexaco Inc.
InventorsWard Edward Schultz, Harry Davis Smith, Jr., Philip France McKinlay
Life of this patent
Estimating the term…
Abstract
A pulsed source of high energy neutrons is used to irradiate the earth formations in the vicinity of a well borehole. Gamma rays produced by the inelastic scattering of the fast neutrons are observed in four energy regions of the gamma ray energy spectrum corresponding to the inelastic scattering of neutrons by carbon, oxygen, silicon and calcium. Signals representative of the carbon/oxygen, calcium/silicon and carbon plus oxygen gamma rays observed are developed. By appropriately combining these signals with a separately derived hydrogen index log the quality of coal bearing formations or oil shale regions penetrated by the borehole may be determined.
Claims10
A method for locating and determining the quality of coal beds traversed by a well borehole comprising the steps of:
- passing a well tool having a pulsed source of fast neutrons and radiation detector through a well bore;
- repetitively irradiating the earth formations in the vicinity of the well bore with relatively short duration bursts of fast neutrons;
- detecting, during said neutron bursts, gamma rays resulting from the inelastic scattering of fast neutrons by carbon and oxygen, in earth formations in the vicinity of the well bore and generating signals representative thereof;
- generating signal representative of the carbon/oxygen ratio of inelastic gamma rays in earth formations in the vicinity of the well bore;
- determining the location and the quality of said coal beds by comparing said carbon/oxygen ratio signal with a predetermined relationship of said carbon/oxygen ratio signal as a function of the BTU content of coal.
A method for locating and determining the quality of oil shale zones traversed by a well borehole comprising the steps of:
- passing a well tool having a pulsed source of fast neutrons and a radiation detector through a well bore;
- repetitively irradiating the earth formations in the vicinity of the well bore with relatively short duration bursts of fast neutrons;
- detecting, during said neutron bursts, gamma rays resulting from the inelastic scattering of fast neutrons by carbon and oxygen in earth formations in the vicinity of the well bore and generating signals representative thereof;
- generating a signal representative of the carbon/oxygen ratio of inelastic gamma rays in earth formations in the vicinity of the well bore;
- determining the location and kerogen content of said oil shale zones by comparing said carbon/oxygen ratio signal with a predetermined relationship of said carbon/oxygen ratio signal as a function of the kerogen content of said oil shale.
Dependencies are inferred from the claim text.