Coupling Analysis on Permeability and Pore Fracture Development in High Rank Coal Reservoirs of Southern Qinshui Basin

Abstract

To analyze the coupling relationship between permeability of high rank coal reservoir and pore and fracture development, taking No.3 coal reservoir in southern Qinshui Basin as the research object, and pore structure was studied by fractal theory. Fractal characteristics, using geometric fractal model to calculate the contribution ratio of different pore size to coal and rock permeability, linearly fitting the correlation between permeability and pore fractal dimension, volume percentage, Ro,max and other factors. The results show that the pore-fracture volume is mainly micro-pore, and the specific surface area ratio is the highest; the pore type is mainly semi-closed pore; the average porosity of coal sample is 4.652%, and the average permeability is 8.68×10-5 μm2. The contribution of macro-pore and fracture to permeability is 99.809%, and the permeability of 3# coal reservoir in southern Qinshui Basin is mainly comes from the contribution of macropores and fractures. There is a weak correlation between permeability, porosity and Ro,max, which increases first and then decreases with the increase of metamorphic degree. Permeability is positively correlated with fractal dimension of mesopore, macropore and fracture, and negatively correlated with fractal dimension of micropore.

Keywords

• mercury intrusion method
• low-temperature liquid nitrogen adsorption
• fractal dimension
• porosity
• permeability