| By the affection of regional tectonic-thermal evolution, the coal reservoirs have undergone the plutonic metamorphism, tectonic-dynamic metamorphism and magmatic thermal metamorphism, and they were caused into different degrees of metamorphic and deformation in the south of Qinshui Basin, and where also went through three periods of tectonic stress field. The reservoirs possess different characteristics in many aspects of physical properties, such as metamorphic and deformation, gas bearing capacity and permeability. Those characteristics control the enrichment and the high permeability of coalbed methane. There are great significance in reality and theory by researching aboves.In this paper, Qinshui Basin is picked as the study area, which is a poupular area for coalbed methane esploration, because of the peogress and shortcomings of the current research in coalbed methane exploration. And the samples were collected from Gaomiaoshan Fault to Sitou Fault, where contain 3 regions and 7 representative coal mines. According to the micro-macro observation of structure, fracture occurrence statistics and vitrinite reflenctance ananlyse, fluorescence microscopic and field-emission scanning electorn microscropic obvervation, mercury injection experiment and low temperature nitrogen adsorption analyse, Micro-CT scanning and permeability testing, this paper mainly discusses the characterics of the vitrinite reflenctance anisotropy, the characterics of pore-fracture in coal and its fractal characterics and the tectonic differentiation of coalbed methane enrichment areas. The following conclusions can be achieved:1. Reservoir parameters of coalbed methane enrichment areas in Qinshui BasinAccording to the characterics of the vitrinite reflenctance anisotropy, the characterics of pore-fracture in coal and its fractal characterics, the degrees of structure deformations can be setted quantitatively by using natural deformation coefficient (εs) and the fractal dimension of pore-fracture (D). By the research of this thesis,3 different types of coal reservoirs in study area are summarized.Type I:when 0.2<εs<0.4 and 1.4<D< 1.7, high gas bearing capacity and permeability, high productivity, high economical recovery factor;TypeⅡ:whenεs>0.4 and D>1.7, medium gas bearing capacity and permeability, medium productivity, medium economical recovery factor;TypeⅢ:whenεs<0.2 and D<1.4, low gas bearing capacity and permeability, low productivity, low economical recovery factor。2. Enrichment parameters of coalbed methane enrichment areas in Qinshui Basin(1) According the fractal dimension of pore, the pore natural behavior law of the mutation of incremental pore volume, the characterics of proliferation and flow and the mean free path of moleculars in coalbed methane, the coal pore can be bouned at 0.06μm (ie 60nm), dividing into seepage pores and adsorption-diffusion pores, which are up to 60nm, or blew 60nm.(2) The nitrogen adsorption in the coal mylonitic coal (SH-12) in the same coal rank is far more than other brittle deformation coals. It can be seen that the metamorphism has little effect on nano-pore of deformed coals, while the deformation grasps the handle.3. Seepaging parameters of coalbed methane enrichment areas in Qinshui Basin(1) It's the first time to create the minmum effective aperture (ro,min) and effective seemly pore throat ratio (λ0) to characterization of the flow of coal pore structure.The ro,min has great important influence on the flow, and theλ0 shows the relative homogeneity of the r0,min in effectively connected space. Those parameters control the permebility and the economical recovery factor of the coal reveior. The mercury withdrawal efficiency (We) reflects the recovery factor of capolary effect in non-wetting phase. The higher the We, the higher the fluid recovery in the coal reservoir. These three parameters have some correlations, ie, the ro,min andλ0 are in a negative exponential correlation, and theλ0 and We are in a negative correlation.(2) The relationships between the fractal dimensin of pore- fracture and the deformation in coal resvoir are more closely.The fractal dimensin of pore will be increases with theεs, and will take place significant changes in wave-type.With the increasing of fractal dimensin, theεs increases significantly, meanwhile, theεs and the fracture density are positively correlated, that is, the stronger the deformation, the greater the fracture density. That is to say that the tectonic stress is the main reason that makes the fracture increase.(3) According to the Micro-CT scanning to 6 coal samples of different degrees of metamorphic and deformation, it found that the Micro-CT scanning technology has the adventages of characterizing the pore-frature fully.3-D visualization results show that if the space configuration among pore-fructure the same type of deformed coal is different, the permeability is quite different too.4. The coalbed methane enrichment areas show obvious regional differentiationThe coalbed methane enrichment areas show obvious regional differentiation and form three NE-NNE structural regions, which have the same spreading direction with the direction of synclinorium spindle and magma intrusion in Yanshan period. The structural regions are Zaoyuan-fanzhuang region (TREND 1), Sidi-chengzhuang region (TREND2) and Zhengzhuang region (TREND3). Their gas content and permeability possess obvious distribution in EW and SN. From east to west, the gas content and permeability in TREND 1, TREND2 and TREND3 reduce one by one. From south to north, the TREND1 can also be divided into three parts: Panzhuang block (1A), Zaoyuan block and Hudi-pichi block (1B) and Fanzhuang block (1C). The gas content and permeability is best in 1 A, medium in 1B, low in 1C. |
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