Q&A Session with Dr. Mustafa Rarabi

Jul 29, 2024

Q&A Session with Dr. Mustafa Rarabi

Welcome and introductions by Mia. Dr. Mustafa Rarabi addresses questions related to reservoir characterization, unconventional reservoirs, and other topics in petroleum engineering.

Main Topics Covered

1. Differentiation Between Organic Matter and Dolostone

  • Organic matter showing uranium readings and dolostone also showing uranium readings can be differentiated using spectral gamma ray.
  • Key Factors:
    • Lamination: Seen in source rocks but not in dolostone.
    • High resistivity: Source rocks show high resistivity, dolostone does not.
    • Porosity: Source rocks usually have low porosity.
    • Dolomite can also be a source rock.
  • Gamma-ray, Neutron, and Density Logs:
    • Gamma-ray high in front of clay, low in reservoir layers.
    • Neutron porosity: Reads high in clays due to hydrogen content.
    • Density tool measures density which can be converted to porosity using the equation [Φ = (ρ_{matrix} - ρ_{bulk}) / (ρ_{matrix} - ρ_{fluid})].
    • Consistent porosity scales:
      • Sandstone: Reads lower porosity in neutron tool.
      • Limestone: Reads true porosity.
      • Dolomite: Reads higher porosity in neutron tool.
    • Photoelectric Method (PE): Differentiates lithology with PE values – 2 (Sandstone), 3 (Dolomite), 5 (Limestone).
    • Expensive Solution: Running a spectral gamma ray to confirm high uranium levels.

2. Queries about Logs and Tools

  • LWD in Vertical Wells:
    • Can be used but requires expertise due to environmental conditions (rotation, circulation, vibrations).
  • Tool Centralizers: Used to centralize tools during logging to ensure accuracy.
  • Focused Resistivity: Current is focused via guards to prevent leakage through mud.
  • Phase Shift and Amplitude in Induction Logs:
    • Differ when crossing bed boundaries, but in the same formation, they agree.

3. Unconventional Reservoirs

  • Clay as Source Rock: Not possible; clays will never be a reservoir.
  • Low Permeability: Due to very fine grains in unconventional reservoirs leading to small pore sizes.

4. Additional Questions

  • Gamma-ray tool vs Gamma-Gamma tool: Gamma-ray tool doesn't have a source, reads natural gamma. Gamma-Gamma tool has a gamma source.
  • Resistivity and Mud Invasion: Measured resistivity must account for flushed and invaded zones for accurate deep zone resistivity.
  • Suggested Reading:
    • Advanced: Well Logging for Earth Scientists by Darwin Ellis.
    • Basic: Basic Well Logging Analysis by George Asquith and Daniel Krygowski.

Follow-up Questions

  1. Azimuth and Inclination: Planned during well planning and measured during/after drilling.
  2. Kozny-Carman Equation: Accounts for porosity and tortuosity, which relates to pore throat diameter.
  3. Barite Impact on PE Reading: Heavily affects shallow measurements. Corrections are available but not recommended.
  4. Oil Migration from Low Porosity Rocks: Takes millions of years; low permeability maintains hydrocarbon storage.
  5. Low Resistivity in Reservoirs: Can be bad due to water or good due to fine grains or lamina (low resistivity pay).
  6. Permeability and Fluid Saturation: Depends on whether it's absolute permeability (no) or relative permeability (yes).
  7. Real-time Data Acquisition: Advanced tools allow for real-time data transmission, a well-established technology.