Research On Permeability Improvement Mechanism Of Different Rank Coal Using Multi-component Acid

The characteristics of low coal reservoir permeability in China decided to develop coal bed gas, need to transform the coal reservoir. Hydraulic fracturing and other physical traditional ar way can improve the coal reservoir flow capacity in a certain extent, but its effect to mineral fill in coal pores and fissures is little. These minerals greatly reduces the conductivity of coal reservoir, If select a kind of acid formulation, dissolution the minerals filling in coal reservoir hole fracture through chemical reaction with it, increase the flow capacity of filled hole fracture and to improve coal reservoir permeability, that has important significance for development of China's low permeability coal bed methane.This paper collected representative samples of different rank coals, first has carried on the test of mineral content of different rank coals, then carried on the corrosion experiment between silicate minerals(kaolinite, illite, montmorillonite, quartz), carbonate minerals(calcite, dolomite) and sulfide(Huang Tie mine) and different concentration of acid solution(HCl, HF,CH3COOH), obtained the corrosion kinetics equation of different minerals in different acid solution. and carried on the corrosion experiment between different formulations acid and different rank coals, optimized the acid the best multi-component formula of different rank coals. According to the scanning electron microscope and the fractal geometry theory, study the morphology and fractal characteristics of coal surface faces pole fracture before and after acidification, the results show that mineral fill in hole fracture of the different rank coals corrosion after acidification, crevice becomes relatively simple, fractal dimension decreases. By X ray diffraction and Raman spectroscopy experiments, research the variation of chemical structure of different rank coals before and after acidification. The results show that coal macromolecular structure remains unchanged before and after acidification, the effect of acid on coal structure was weak. By the mercury injection experiment and permeability test, study the variation of distribution and permeability of different rank coal pore size before and after acidification, The results showed that coal porosity and permeability increase before and after acidification, and the pore connectivity became better, the mineral content of coal and the original fracture have a great influence on permeability increasing,The more coal fracture development and the content higher of minerals in coal, the acidification better. This study provides a theoretical guidance for the application of multi-component acid in coal bed methane development.