Experimental Study on Compaction Deformation and Gas Permeability Properties for Crushed Limestone

Area of Science:

• Geotechnical Engineering
• Petroleum Engineering
• Mining Engineering

Background:

• Mining goafs contain significant coalbed methane (CBM) resources, necessitating efficient extraction methods.
• Understanding the gas permeability of crushed coal and rock in the caved zone is crucial for CBM migration and enrichment studies.

Purpose of the Study:

• To investigate the compaction deformation and gas permeability properties of crushed limestone with varying particle sizes.
• To establish the relationship between porosity, particle size, stress, and gas permeability in crushed limestone.

Main Methods:

• Experimental analysis of crushed limestone samples under varying stress conditions.
• Measurement of porosity, deformation, and nitrogen permeability.
• Analysis of particle size distribution and its effect on permeability.

Main Results:

• Crushed limestone's deformation resistance increases with stress; porosity changes differ across particle sizes and compression stages.
• Permeability ranges from 10^-12 to 10^-10 m², decreasing with porosity and nitrogen pressure.
• Nitrogen migration requires a pseudo-threshold pressure gradient (64.86–311.42 Pa/m).
• Larger particle sizes (5-10 mm) exhibit significantly higher permeability growth amplitude compared to smaller ones (0.315-0.63 mm).
• Permeability is notably higher in crushed limestone on the sides of the lower layer in the caved zone.

Conclusions:

• Particle size and porosity are key factors influencing gas permeability in mining goaf crushed rock.
• Findings aid in accurately predicting CBM enrichment zones and optimizing extraction well placement.