A Parameters Extraction Method Of Rock Pore Based On Digital Image Analysis

Rocks are the main medium of a groundwater motion and storage, the study of rock pore, fracture and solution fissure is helpful to infer the permeability of rocks and water storage, so from the view of pores in different kinds of rocks, hydrogeology parameters extraction has great significance for further understanding of hydraulic properties and it’s useful to get a more particular knowledge of water-physical properties. Traditional methods of measuring the parameters of the rock pore are based on Darcy’s law, which works in condition of steady flow. But for the low permeability of aquiferous medium, especially in view of the low permeability rock, fluid in the migration process is affected by the viscous force has greater effect than the inertia force, Darcy’s law is no longer applicable. Traditional methods have certain limitations on the measurement range and unable to get ideal results. Geological repository sites selecting which for high-level nuclear waste disposal in our country is in the process of evaluation, studying the distribution of pore and fracture parameters is helpful to analyze the regional water-rock system hydraulic characteristics and transmission characteristics, it also can provide basic data support and evaluation reference. Therefore, in view of low permeability rock, it is necessary to put forward a new kind of hydraulic parameters acquisition method.With the continuous development of digital image analysis technology, the digital image processing technology is applied in many fields widely. On the base of extensive reading the domestic and foreign literature and study of traditional hydrogeology parameters acquisition experiment, this article firstly summarizes the traditional theory and method, then puts forward a novel method for parameter measurement and analysis by using digital image analysis technology for different permeability level of rock pore and fracture. Meanwhile this article establishes a systematic analysis method to identify the rock pore and fracture.Based on different kinds of pore and fracture parameters using digital image processing technology which were put into use of strong permeability rocks like quartz sandstone and low permeability rocks like granite, this research establishes a systematic method in order to identify and analyze rock pore and fracture, and obtain the quartz sandstone porosity, direction angle, shape coefficient, pore radius, perimeters and fracture rate of granite. Statistical results of rock fracture rate reflects the spatial distribution characteristics of F4fault zone and the low permeability rock fracture rate change rules crossing the fault zone, which also provides some basis for the further study of fault structure characteristics.Through the above research, this article draws four conclusions. The main work and result are summarized as follows:(1) The pretreatment of sandstone samples in the experiment and the injecting processing of granite samples can improve the efficiency of image analysis for pores identification. By high temperature and high pressure injecting processing, using digital image analysis method can extract pore and fracture parameters not only from the strong permeability rock like quartz sandstone, but also low permeability rock such as granite. Part of the granite mineral composition distribution. A part of mineral composition distribution can be inferred qualitatively and quantitatively.(2) The digital image analysis method which we put forward in this article can not only extract pore parameters of quartz sandstone with stronger permeability, but also can extract fracture parameters of granite with low permeability coefficient in level of10"6cm/s. The measuring range of this new method more widely than conventional methods, it also can be easily applied to extract the rock parameters of Beishan F4fault. (3)Through analyzing digital images of quartz sandstone samples, this research obtained the rock porosity change curve vs. the size of the image and finally found that the digital images which were1339×1339pixels could be the Representative Elementary Volume (REV) for image analyzing, it could reflect the characteristics of the pore parameters of the digital image effectively.(4) The spatial distribution characteristics of granite fracture rate in F4fault zone shows that the granite is affected by weathering and tectonism, and the farther from fault zone core, the lower the fracture rate we can get. According to the rock permeability classification, the result shows low permeability in F4fault zone area and the rock surface crack rate is in a low range, F4fault zone belongs to extreme low permeable grade. The rocks in this area have limited impact on the water storage and hydraulic conductivity.