| Coalbed methane is generated in coal in the long coalification process, mainly adsorbed in the coal seams, commonly known as gas, it mainly consists of methane. In the coal mining may occur gas explosion, against the safety production of coal, we have considered the gas as a harmful gas, and directly emitted into the atmosphere, then the atmosphere was seriously polluted. With the progress of science and technology and the pattern changing of word energy, more and more country is increasing emphasis on environmental issue,CBM is used as a strategic reserve of energy around the world.Exploitation of coalbed methane can either reduce or eliminate seam gas disaster, but also can be used as natural gas energy in the future, it will become a valuable quality of new clean energy.Sporadic development in the1950s has been mining coal-bed methane, in1953the first bite of coalbed methane production of gas Wells in the SAN Juan basin, coalbed methane production02100-12000m3/d. In the late70s, the large-scale mining of coal bed methane resources have been the foundation. On December12,1980at Oak Grove coal bed in Alabama, the production of the black warrior basin by the end of1994, the United States have been drilling more than6000CBM Wells, there are more than5500CBM Wells put into production, annual output of coalbed gas quantity is21billion m3, which marks the birth of modern coalbed methane industry. Over the years, the United States in the field of coalbed methane exploration and development has accumulated rich experience and technology, and has obtained the remarkable effect, it also incentives carried out in CBM industry all over the world.Coalbed methane (CBM) has entered the stage of commercial development at present, a lot of the development of technology and means are not completed, need to put more effort in further for coalbed methane development every technology of link into the in-depth research, provide more technical support for coalbed methane development. First of all, coal is made up of highly cross-linked macromolecular network and other mutually cross-linked macromolecular chain of porous media; Secondly, coal seam as the CBM angry layer and reservoir, a cleat development, low porosity, permeability, specific surface area is large, low mechanical strength, are susceptible to compression, strong heterogeneity, low reservoir pressure, and the conventional sandstone reservoirs vary greatly. These characteristics determine the coal seam by drilling process easy absorption or adsorption of various gases and liquids, according to these outside into the well liquid need often contains all kinds of additives, the invasion of coal reservoirs will important influence on the surface properties of coal and rock, and coal bed gas and liquid two phase seepage, ultimately affect the high rank CBM development effect. In the drilling fluid invasion of the coal and rock surface properties and percolation features has been no systematic study, in an in-depth study of this aspect is helpful to coalbed methane reservoir damage mechanism and the coalbed methane development present situation analysis, etc.This article selects the different area high rank coal as the research object, by adopting the combination of theory and laboratory test technical route, from the following four aspects of drilling fluid invasion of the coal and rock surface properties were analyzed and the influence mechanism of gas and liquid two phase flow characteristics:(1) To select different mining area high rank coal, the study of the surface properties of coal and rock.(2) The drilling process, considering the need of drilling technology and reservoir protection, tend to add various additives in drilling fluid. In drilling fluid with different surfactants, therefore, to study the effect of surfactants on coal and rock surface properties.(3). Adjust the pH value of drilling fluid, research the surface of the coal and rock properties under different PH values.(4) Coal and rock surface properties and Gas-water interfacial tension will change before and after the drilling fluid invasion, the study of the change of reservoir gas-water percolation characteristics before and after drilling fluid processing, before and after the coal and rock surface properties and Gas-water interfacial tension changed. Research results show that in the process of drilling, drilling fluid invasion of solution caused by the change of coal and rock surface properties Gas-water interfacial tension, especially easy to cause the change of coal reservoir Gas and water seepage. In order to reduce or avoid drilling fluid invasion of coalbed methane reservoir damage, puts forward the protection of drilling fluid additive and improvement of coal reservoir methods during the process of drilling, through the drilling fluid invasion of coal reservoir before and after, the change analysis of coal and rock surface properties, choose suitable for coalbed methane reservoir system of drilling fluid additives, the use of steady state dynamic evaluation method of coal pollution test, determination of the change of gas-water two-phase relative permeability before and after the drilling fluid invasion of coal samples, in order to evaluate whether the drilling fluid additives to protect coal reservoir and improve the seepage characteristics of coal seam. |
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