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FORMATION EVALUATION PETE 321

FORMATION EVALUATION PETE 321. Lab 2 _______ GR. Spring 2005. Sections 501, 502 Dr. David Schechter Lab: Charles Ozobeme. Sections 503, 504 Dr. James Russell Lab: Kalwant Singh. Lab 3 objectives. More information about GR Calculation of Vsh Geographix – PRIZM tutorial. Gamma Ray Log.

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FORMATION EVALUATION PETE 321

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  1. FORMATION EVALUATIONPETE 321 Lab 2 _______ GR Spring 2005 Sections 501, 502 Dr. David Schechter Lab: Charles Ozobeme Sections 503, 504 Dr. James Russell Lab: Kalwant Singh

  2. Lab 3 objectives • More information about GR • Calculation of Vsh • Geographix – PRIZM tutorial

  3. Gamma Ray Log • Natural gamma-ray log is based on the measurement of natural radioactivity of formation rocks, which depends on the content of radioactive isotopes of uranium, potassium and thorium and, also, on the lithological composition of formation rocks. • Types: • Natural • Spectral • Thorium, Uranium, Potassium • Applications: • Correlation. • Lithology indicator • Determining the shale content of rocks. • Introducing depth corrections to other well logs. • Detection of radioactive minerals. • Paleoenvironmental indicator

  4. Gamma Ray Log Interpretation The interpretation of gamma ray logs can be summarized as follows: • Clean sands, sandstones, limestones, and dolomites have low radioactivity. Anhydrite, salt, lignite and coal have also a low radioactivity. • Ordinary shales have a much higher radioactivity than the rocks listed above. Shales are sufficiently high in radioactivity and can generally be easily distinguished from the other rocks on a gamma ray log.

  5. Gamma Ray Log Figure: Scintillation Gamma Ray Detector

  6. Gamma Ray Log

  7. Gamma Ray Log Gr max Shale Sand Gr min Shale

  8. Spectral Gamma Ray Log • It is a borehole log indicating the concentration of thorium (Th), uranium (U), and  potassium (K) in the rocks surrounding a borehole. Applications: • Estimate volume and type of clay minerals • Identify fractures • Differentiate radioactive carbonates from shales and clays

  9. Spectral Gamma Ray

  10. Spectral Gamma Ray Log Vs Gamma Ray Log Gamma Ray Log Spectral Gamma Ray Log • It is not able to discern between the gamma-rays from Th, U, and K respectively; it just "counts" the total number of gamma-rays that hits the detector per second. • The "output" is counts per second (cps) that also may be converted to API units for gamma radiation. • It is able to detect and identify the radioactive source (gamma-rays from Th, U, and K respectively.) • It is displayed as three curves from all sources of thorium, uranium and potassium.

  11. Gamma Ray Log

  12. Gamma Ray Log

  13. Gamma Ray Log

  14. Shale Content from GR Log

  15. Shale Content from GR Log

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