A new porosity evaluation parameter based on neutron porosity logging.

Area of Science:

• Geophysics
• Petroleum Engineering
• Nuclear Well Logging

Background:

• Neutron porosity logging is crucial for formation porosity measurement.
• Accurate porosity calculation is challenging in formations with complex mineralogy and fluid properties.
• Existing methods are affected by borehole effects like excavation.

Purpose of the Study:

• To investigate the relationship between neutron slowing-down length, neutron diffusion length, and formation hydrogen index.
• To develop a new parameter for more accurate porosity determination.
• To overcome limitations of traditional neutron porosity logging.

Main Methods:

• Studied the relationship between neutron slowing-down length, neutron diffusion length, and formation hydrogen index.
• Derived a new parameter, the apparent formation hydrogen index, using thermal-neutron flux formula.
• Utilized neutron counting ratio, formation density, and capture cross-section to construct the new parameter.

Main Results:

• The apparent formation hydrogen index closely approximates the true formation hydrogen index.
• The new parameter is unaffected by the excavation effect, a common borehole issue.
• The apparent formation hydrogen index exhibits response characteristics more aligned with the volume physical model.

Conclusions:

• The apparent formation hydrogen index offers a more accurate method for calculating formation porosity.
• This improved accuracy is especially notable in gas-bearing formations.
• The new parameter enhances the reliability of neutron porosity logging in complex geological environments.