COMBINATION OF EPITHERMAL AND INELASTIC NEUTRON SCATTERING METHODS TO LOCATE COAL AND OIL SHALE ZONES

摘要

1451572 Borehole logging TEXACO DEVELOPMENT CORP 31 May 1974 [5 June 1973 15 Feb 1974] 24359/74 Heading G1A In borehole logging, coal beds and oil shale zones are located by measurement of the carbon/oxygen ratio of the formation obtained by irradiating the formation with short bursts of fast neutrons and measurement of gamma radiation resulting from the inelastic scattering of these fast neutrons during the neutron bursts. The sonde of Fig. 1 comprises a deuteriumtritum reaction neutron generator 11 pulsed on for 5 Ásecs at 50 to 200 Ásec: intervals. The output of detector, a NaI or CsI (thallium-doped) crystal 10 coupled to a photo-multiplier 12 shielded by boron from thermal neutrons and by shield 13 of paraffin, carbon, iron, lead or steel from source 11 is gated during the source pulses so as to avoid detection of the neutron capture γ-ray population. Scintillator produced background is discriminated by discriminator 18. The pulse height analyzer 24 selects pulses in the windows shown in Fig. 3. Besides the C/O ratio, C + O and Ca/Si are also recorded at 30. For coal evaluation C/O is indicative of coal quality and oil shales are identified on the basis of their kerogen content. Further logs using a different design of probe may be taken to aid identification of the above mentioned zones and include a gamma ray density log and a Hydrogen index log. Reference has been directed by the Comptroller to Specification 1364572.