Method and apparatus for determining borehole and formation constituents

A method of determining the spectral composition of the contents of a borehole traversing a subterranean formation comprising the steps of:

• bombarding said contents of said borehole and said formation with a source of high energy neutrons positioned in said borehole whereby gamma rays emanate from said contents and said formation in response thereto;
• generating an early capture spectrum signal representative of the gamma rays emanating from said formation and said contents of said borehole;
• generating a late capture spectrum signal representative of the gamma rays emanating from said formation;
• comparing said early capture spectrum signal with an early capture spectrum standard to generate a signal representative of the combined composition of said formation and said contents of said borehole;
• comparing said late capture spectrum signal with a late capture spectrum standard to generate a formation signal representative of the composition of said formation;
• and
• comparing said combined composition signal with said formation signal to generate a signal representative of the contents of said borehole.

A method of determining the composition of a subterranean formation having a borehole traversing therethrough comprising the steps of:

• bombarding said borehole and said formation with high energy neutrons from a source positioned in the borehole;
• generating an inelastic spectrum signal representative of the inelastic gamma rays emanating from said borehole and said formation as a result of neutron excitation;
• generating an early capture spectrum signal representative of the capture gamma rays emanating from said borehole and from said formation;
• generating a late capture spectrum signal representative of the capture gamma rays emanating primarily from said formation;
• comparing said inelastic spectrum signal with an inelastic spectrum standard to generate a first signal representative of the detailed composition of said formation and borehole;
• comparing said early capture spectrum signal with an early capture spectrum standard to generate a signal representative of the combined composition of said formation and said borehole;
• comparing said late capture spectrum signal with a late capture spectrum standard to generate a formation signal representative of the composition of said formation;
• comparing said combined composition signal with said formation signal to generate a signal representative of the composition of said borehole;
• and
• comparing said first representative signal with said signal representative of the composition of said borehole to generate a corrected signal representative of the detailed composition of said formation.

A method of determining the composition of a subterranean formation having a borehole traversing therethrough comprising the steps of:

• bombarding said borehole and said formation with high energy neutrons from a source positioned in the borehole;
• generating an early capture spectrum signal representative of the capture gamma rays emanating from said borehole and said formation;
• generating an late capture spectrum signal representative of the capture gamma rays emanating primarily from said formation;
• comparing said early capture spectrum signal with an early capture spectrum standard to generate a signal representative of the combined composition of said formation and said borehole;
• comparing said late capture spectrum signal with a late capture spectrum standard to generate a formation signal primarily representative of the composition of said formation;
• comparing said combined composition signal with said formation signal to generate a signal representative of the composition of said borehole;
• and
• comparing said formation signal primarily representative of the composition of said formation with said signal representative of the composition of said borehole to generate an improved signal representative of the composition of said formation.

Apparatus for deriving the spectral composition of material adjacent a well-logging sonde positioned in a borehole traversing a subterranean formation, said sonde irradiating said material with fast neutrons thereby generating gamma rays, comprising:

• means for generating an early capture signal representative of the gamma rays emanating from said material and said formation during a first time interval;
• means for generating a late capture signal representative of the gamma rays emanating from said formation during a second time interval;
• means for deriving a combined spectral analysis signal of said material and said formation from said early capture signal;
• means for deriving a formation spectral analysis signal of said formation from said late capture signal;
• and
• means for comparing said formation spectral analysis signal with said combined spectral analysis signal to derive a signal representative of the spectral composition of said material adjacent the well-logging sonde.