A Dual-Media Permeability Model for Coal Featuring Dynamic Slip Factor: Incorporating Heterogeneity, Stress and...

Area of Science:

• Geosciences
• Petroleum Engineering
• Material Science

Background:

• Accurate prediction of coal permeability is vital for efficient coalbed methane (CBM) extraction.
• Traditional models often overlook matrix permeability, use empirical slip factors, and inadequately weigh multiple influencing mechanisms.
• Understanding dynamic permeability changes is key to optimizing CBM recovery and reservoir management.

Purpose of the Study:

• To develop a dual-medium apparent permeability model for coal that incorporates heterogeneity, stress, adsorption, and slip effects.
• To quantify the regulatory mechanisms of heterogeneity and stress on the slip factor.
• To analyze the influences of heterogeneity, stress, adsorption, and slip on coal permeability variations and evaluate their relative contributions.

Main Methods:

• Development of a novel dual-medium apparent permeability model for coal.
• Quantification of heterogeneity and stress effects on the slip factor.
• Analysis of permeability changes under varying conditions of roughness, fractal dimension, effective stress, and gas pressure.

Main Results:

• Permeability decreases with increasing roughness, an effect amplified by higher effective stress.
• Effective stress significantly reduces permeability by constricting pore and fracture apertures.
• Heterogeneity and effective stress jointly influence the slip effect, with effective stress being the dominant factor in permeability reduction.
• The interplay between slip and stress effects on permeability is pressure-dependent, with slip dominating at low pressures and stress at high pressures.

Conclusions:

• The developed model provides a more comprehensive understanding of coal's dynamic permeability changes.
• Effective stress is identified as the most critical factor influencing coal permeability, necessitating its accurate inclusion in predictive models.
• The findings offer theoretical support for optimizing coalbed methane extraction strategies by accounting for complex permeability behaviors.