USC_Sec_7_Gamma_Ray_Log_doc

USC_Sec_7_Gamma_Ray_Log_doc - University of Southern...

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University of Southern California Department of Petroleum Engineering Fall, 2007 PTE-461 Formation Evaluation Section 7: Natural (Passive) Gamma Ray Log Donald G. Hill, Ph.D. California Registered Geophysicist 170 California Registered Geologist 6043 Kentucky Registered Professional Geologist 1624 Texas Licensed Professional Geophysicist 6289 Consulting Petrophysicist: Petrophysics, Shallow Geophysics, Borehole Geophysics, and Subsurface Geology Planning, Oversight, and Interpretation 1012 Hillendale Ct +(925) 437-5748 Cell Walnut Creek, CA +(309) 420-7354 FAX USA 94596 +(925) 947-1541 Home http://www.hillpetro.com <dgwhill@aol.com>
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USC PTE-461, Basic Petrophysics - Fall, 2007 Section 7: Natural (Passive) Gamma Ray Log Donald G. Hill, Ph.D., R.Gp, R.G., R.P.G., L.P.Gp. Page: 7-2 dgh@hillpetro.com Table of Contents Subject Page Introduction 7-4 Gamma Ray Logs 7-4 Historical Background 7-4 Rationale for Running (Passive) Gamma Ray Logs in Petroleum Wells 7-6 Natural Gamma Ray Log Operating Principles 7-6 Natural Gamma Ray Sources 7-6 Gamma Ray Detectors 7-7 Total Count Detectors 7-9 K-U-T Spectral Gamma Ray Detectors 7-11 High Purity Germanium Detectors 7-12 Statistical Processes and Counting Statistics 7-12 Gamma Ray Log Calibration 7-15 Gamma Ray Detector Efficiency and Count Rate Stability 7-19 Gamma Ray Repeat Sections 7-19 Logging Speed and Time Constants or Logging Windows 7-22 Gamma Ray Detector Size, Efficiency, and Signal Splitters 7-24 Larger Sized Slim-Hole NaI Crystal Scintillation Detectors 7-27 Suggested Gamma Ray Repeatability Measures 7-27 Gamma Ray Logs as a Sand/Shale Indicator 7-29 V sh Models 7-29 Bi-Modal Model and V sh 7-31 Gamma Ray Log Shale Volume Disclaimer 7-32 References 7-33 Vendor Websites 7-41 Other Websites 7-41 Appendix A: API Radio-Activity Log Test Pit Standards 7-42 Tables No Tables Figures Figure 7.1: Typical NaI Crystal Natural Gamma Ray Spectra 7-4 Figure 7.2: 232 Th, 40 K, and 238 U Radioactive Decay Series 7-5 Figure 7.3: Naturally Occurring Radio-Nuclide Gamma Ray Spectra 7-7 Figure 7.4: Log Header Page 2, Showing Information about the Gamma Ray Detector 7-8 Figure 7.5: High Resolution Gamma Ray Spectra from South Texas 7-10 Figure 7.6: Comparison of Gamma Ray Logs by 1" x 4" NaI Scintillation Crystal Detectors from Two Different Fabricators 7-13 Figure 7.7 API Gamma Ray Logging Tool Test Pit 7-14 Figure 7.8: Gamma Ray Field Calibrator 7-15
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USC PTE-461, Basic Petrophysics - Fall, 2007 Section 7: Natural (Passive) Gamma Ray Log Donald G. Hill, Ph.D., R.Gp, R.G., R.P.G., L.P.Gp. Page: 7-3 dgh@hillpetro.com Figure 7.9: Example of an Analogue System Gamma Ray Tool Calibration Pigtail 7-16 Figure 7.10: Example of a Poor Statistical Stability Check for a 1" x 4" NaI Crystal Scintillation Detector in Low Radioactivity Materials 7-18 Figure 7.11: Example of a Poor Statistical Stability Check for an 18" Geiger-Mueller Tube Detector, in Low Radioactivity Materials 7-18 Figure 7.12: Example of a Good Gamma Ray Repeat 7-20 Figure 7.13 Poor Repeat Agreement From a 1" x 15" Geiger-Mueller Tube Slim-Hole Detector, in a Low Radioactivity Section 7-21 Figure 7.14 Poor Repeat Agreement From a 1" x 4" NaI Crystal Scintillation
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USC_Sec_7_Gamma_Ray_Log_doc - University of Southern...

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