Numerical study on determining formation porosity using a boron capture gamma ray technique and MCNP

Area of Science:

• Geophysics
• Nuclear Well Logging
• Petrophysics

Background:

• Accurate formation porosity determination is crucial for hydrocarbon exploration and reservoir management.
• Pulsed neutron-gamma (PNG) logging tools are widely used for subsurface formation evaluation.
• Existing methods for porosity estimation using PNG tools face challenges with signal-to-noise ratio and sensitivity.

Purpose of the Study:

• To evaluate the effectiveness of the boron capture gamma ray counting ratio for formation porosity determination.
• To investigate the impact of water salinity and wellbore diameter on porosity measurements.
• To assess the benefit of a boron lining in improving measurement accuracy.

Main Methods:

• Simulations using the Monte Carlo method were performed to model thermal neutron distribution and gamma ray spectroscopy.
• The boron capture gamma ray counting ratio was analyzed using near and far detectors in a pulsed neutron-gamma tool.
• Porosity response was evaluated across various water salinities and wellbore diameters.

Main Results:

• The boron capture gamma ray counting ratio demonstrated higher sensitivity for porosity determination compared to total capture gamma.
• A boron lining was found to significantly improve the signal-to-noise ratio of the measurements.
• Simulation results provided insights into tool response under different formation conditions.

Conclusions:

• The boron capture gamma ray counting ratio is a viable and sensitive method for formation porosity logging.
• Implementing a boron lining in PNG tools can enhance measurement accuracy and reliability.
• Monte Carlo simulations are effective for optimizing PNG tool design and interpretation.