A Research On Mechanism And Technological Principle Of Enhancing Coalbed Gas Extraction Rate By Ultrasonic Vibrating

Because coalbed gas is mainly deposited connected pores as adsorbed gas, the producing process is a complicated procedure of desorption/diffusion/permeation. To enhance the efficiency of gas exploitation, a lot of driving technologies are applied, such as holing, fracturing, gas injecting, loosing which are successful in increasing the extraction of methane. However, commercial exploitation and utilization hasn't by far formed due to the geographically complicated structure of coal field, low permeability of coal bed and low gas extraction which lead to low outputting. In terms of the character of poor permeability in coal bed, a physically driving Ultrasonic technology is brought up in the dissertation to stimulate desorption/diffusion/ permeation of coalbed gas. It is expected to develop a new sound vibrating method to form mechanical disintegration and increase the system temperature in coal particles. Whereas, as to the operating mechanics about sound field's in stimulating gas desorption/diffusion/ permeation quite a lot expmerimental researches in lab are required. So this dissertation tends to explore a keen research on this. The thorough dissertation consists of six chapters.Chapter one presents literature review of the contemporary research at home and abroad on gas adsorption and permeability, and sets down researching contents and technological route.Chapter Two studies a variety of problems including pore characters of different metamorphic coals, specific surface area, characters of gas adsorption and desorption with and without Sound field, and operating mechanics about Sound field's in stimulating gas desorption/diffusion/ permeation.Chapter three analyzes three diffusion models, such as unipore diffusion model, bidisperse diffusion model and isotherm and adsorption rate models. With the reference to the reasoning of bidisperse diffusion model, a simplifying bidisperse diffusion model is composed. What's more, macropore and micropore diffusion coefficients are also got by comparing experimental data with simulating ones. And then, a new idea, apparent diffusion coefficient, was brought up in this dissertation. Using apparent diffusion coefficient represents the factors like gas pressure and characters of coal seam on adsorption/diffusion procedures. And then this chapter demonstrates how Ultrasonic energy is inverted into thermo power which changes heat balance of system and material transfer. Then material balance equation and heat equation of solid-gas system is deduced out under Ultrasonic sound effect. The deduction also sets up a conceptual model on gas desorption /diffusion as adsorbed gas in micropores of coal matrix under Sound field. It also estimates under Sound field operation the characteristic changes in temperature pattern and physical parameters caused during solid-gas desorption/diffusion as adsorbed gas in micropores of coal matrix under Sound field. (i.e. apparent diffusion coefficient, dynamic free gas fraction, and dynamic adsorbed gas fraction).Chapter Four, firstly, experiments coal's permeating characters with and without the operation of Sound field. It is shown in experiments that permeability of coal is closely related to stress, temperature and Sound field: with the same stress and temperature field, ultrasonic will enhance coal permeability. Secondly, a coupling mathematical model including stress, temperature, pressure fields and interrelated physical parameters, such as porosity, bulk modulus, Poisson's ratio, was deduced with single methane mass, heat and stress balance equations between as free gas in connected cleats and fractures and as adsorbed gas in coal matrix under Sound field. Some obvious outputs with Matlab simulating are presented: enhanced coalbed's temperature, promoted methane desorption and diffusion, improved methane's permeability, reduced the value of coalbed's stress. Thirdly, its operating mechanics lies in ultrasonically mechanical vibrating effect, heating effect and vibrating damage to coal rocks.Based on the experimental research and analysis from Chapter Two to Four, referring to the fact that Ultrasonic wave can stimulate gas desorption and permeability, Chapter five tentatively brings about a plan to enhance gas permeability by applying sound vibrated within regionally pre-extracted coal gas.Chapter Six sums up the important conclusion and innovation, and then suggests some questions for further research.