Extracting Pore and Fracture Parameters of Porous Rocks Using a Method Based on Digital Image Analysis

Abstract:

The characterization of pore and fracture is an important part of regional hydrological survey. Traditional methods (e.g. mercury intrusion, porosimetry, and pressure pulse) can effectively determine the parameters of pore and fracture for high-permeability rocks. However, these methods tend to fail for low-permeability rocks, especially quartz sandstone and granite. Thus, this work presented a novel method to determine the parameters of pore and fracture by analyzing the digital image of the casting thin sections under a microscope. Firstly, the size of representative elementary image was obtained by calculating pore parameters of different scales of samples. Then the method based on representative elementary image analyzed the casting thin sections of sandstone with low permeability, low anisotropy, and high water-binding capacity, and determined the parameters such as porosity, round-hole rate, roundness. Besides, this method analyzed the casting thin sections of low-permeability granite from Beishan, Gansu, China to determine more parameters such as fracture rate, length-width ratio of fracture, direction angle, and roundness. Finally, these parameters determined by the method were compared with those by transient pressure pulse method. The comparison demonstrated that the presented method can determine more high-accuracy parameters than transient pressure pulse method.

Key words: digital image analysis, casting thin sections, pore, fracture, parameters analysis