Method and apparatus for neutron induced gamma ray logging for direct porosity identification
In a neutron induced gamma ray well logging instrument, a neutron generator is pulsed at a clock frequency of 20 khz. Each neutron burst produces inelastic scattering gamma rays which are detected during a first time interval coinciding with the neutron source being on. Capture gamma rays are detected during a second interval subsequent to the end of each neutron burst. Upon detection of the scattered gamma rays, a detection pulse is transmitted during each of the two detection intervals. Sync pulses are generated at a scaled down frequency rate of 200 hz within the well logging instrument for transmission to the earth's surface. The scaled-down sync pulses are applied to a phase-locked loop system for regenerating the sync pulses to the same frequency as that of the clock frequency used to pulse the neutron source and to open the detection gates in the borehole instrument. The regenerated sync pulses are then used in surface instrumentation to route the pulse occurring during the inelastic scattering interval to one section of a multi-channel analyzer. Similarly, the pulse occurring in the capture interval is routed into another section of the multi-channel analyzer. The use of memory address decoders, subtractors and ratio circuits enables both a carbon/oxygen ratio and a hydrogen/iron ratio to be obtained, substantially independent of chlorine content of the borehole and formation.
- Assignee:
- Dresser Industries Inc
- Patent Number(s):
- US 4239965
- Application Number:
- TRN: 81-007578
- OSTI ID:
- 6530344
- Resource Relation:
- Patent File Date: Filed date 5 Mar 1979
- Country of Publication:
- United States
- Language:
- English
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