Pore Structural Features of Granite under Different Temperatures.

Area of Science:

• Geotechnical Engineering
• Materials Science
• Petrology

Background:

• Understanding thermal effects on rock properties is crucial for geothermal energy extraction and geotechnical projects.
• Granite's pore structure significantly influences its mechanical and thermal behavior under elevated temperatures.
• Existing models for permeability prediction may not accurately represent high-temperature conditions in tight granite reservoirs.

Purpose of the Study:

• To investigate the impact of thermal treatment on the pore structural characteristics of granite.
• To analyze changes in pore size distribution, porosity, and connectivity with increasing temperature.
• To modify the Winland model for improved permeability prediction in high-temperature granite.

Main Methods:

• Granite samples were subjected to thermal treatment ranging from 25 °C to 400 °C.
• Scanning Electron Microscopy (SEM) and mercury injection experiments were employed to analyze pore structure.
• Capillary pressure curves, pore-throat ratios, median saturation pressure, median pore-throat radius, porosity, pore volume, and pore size distribution were evaluated.

Main Results:

• Thermal treatment led to increased mercury ejection efficiency and enhanced pore connectivity, indicated by decreased pore-throat ratio and median saturation pressure.
• Median pore-throat radius and porosity increased exponentially with temperature, with substantial rises observed above 200 °C.
• Pore volumes, particularly transitional pores and mesopores, increased significantly with temperature, contributing more to the total pore volume.

Conclusions:

• Elevated temperatures promote the development of granite's pore structure, leading to more extensive pore size distribution and enhanced connectivity.
• The modified Winland model demonstrated improved prediction accuracy for macro-permeability based on micropore characteristics at high temperatures.
• Findings provide essential data for optimizing rock geothermal mining projects and related geotechnical engineering applications.