The Analysis Of Coal Reservoir Physical Properties And Geological Factors In Southern Qinshui Basin

Choosing No. 3 coal of the Shanxi formation and No.15 coal of the Taiyuan formation as research objects, this paper applied several methods including geological analysis, samples observation and experiment to study the physical properties like petrologic characteristics, pore and fissure system, permeability and gas saturation and their geological controlling factors, which includes sedimentary environment, structural effect, buried depth, geostress and hydrogeology. Meanwhile, the paper compared the differences of physical properties and their controlling factors between No.3 coal and No.15 coal in the aspects of coal petrology, coal metamorphism, sedimentary environment and buried depth, providing some theoretical basis for the coal bed methane exploration and development.According to the samples observation, the macroscopic types of No.3 and No. 15 coals are mainly semi-bright. Through the microscope and scanning electron microscope analysis results, it can be concluded that vitrinite has the highest content, approximately 80%, inertinite accounts for less than 20%, and no exinite. Minerals in the coals, in descending order, consist of clay minerals, pyrite and calcite. Compared with No. 3 coal, No. 15 coal has higher content of vitrinite, pyrite and calcite. Based on the proximate analysis of coal and vitrinite reflectance, No.3 and No. 15 coals are both highly metamorphic lean coal-anthracite. The vitrinite reflectance of No. 15 coal is slightly higher than that of No. 3 coal; while the volatile yield of the former is a little lower than the latter.By means of scanning electron microscope analysis, the four types of pores including primary pore, secondary pore, exogenous pore and mineral pore are all found in the coals, of which primary pore, blowhole and mineral pore are the most common ones. The exogenous fissure in the coal includes tensile fissure and shear fissure, most of which are mesopore, the content of endogenic fissure is not so much as exogenous fissure. The situation of minerals plugging the pore and fissure system is more common in No.15 coal than in No.3 coal. Generally, the permeability of coal bed in the study area is obviously oriented, and the permeability of No. 3 coal is higher than that of No. 15 coal. The content of CBM in the two coals is high, so is their absorbability.By analyzing sedimentary facies, buried depth, structural effect, geostress and hydrogeology, it can be concluded that the sedimentary environment controlled coal seam thickness, trap ability and methane yields potential, which makes it the most important controlling factor. Tectonic movement was active after coal-accumulating process, therefore it caused great influence on yield of CBM, reservoir space and so on. Through controlling the adsorbance of CBM, the degree of coal metamorphism and the pressure of above formations, buried depth can affect the CBM content. Geostress has adverse effect to the coal reservoir permeability. Hydrogeological conditions have greater unfavorable influence on No. 15 coal than on No. 3 coal.