| Coal bed methane (CBM) is a type of unconventional natural gas and its source and reservoirs in the same coal seam, which is maily adsorbed to the coal reservoir. It is very important clean energy of unconventional oil and gas with abundant resources, low degree of exploration and great development potential. As high-quality and new clean energy, the resource of CBM of which buried depth is less than 2000m is about 36.8x1012 m3 in China. It's mainly distributed in Ordos Basin, Qinshui Basin, Junggar Basin, Erlian Basin, Tuha Basin, Tarim Basin, eastern Yunnan and western Guizhou areas. The target strata mainly include Paleozoic carboniferous, Permian and Mesozoic Triassic, Jurassic and Cretaceous formations. The exploration and development of CBM can meet the growing domestic demand for natural gas and it is very significance for coal safety issues and low carbon constraints in developing countries. But the adsorption of coal makes the reservoiring mechanism, enrichment degree, exploration and development technology of CBM reservoirs very different from conventional natural gas. How to make research on the anisotropy and heterogeneity of coal seam and predict coal seam thickness, gas content, coal reservoir fracture development zone and CBM enrichment area for well deployment is the extremely urgent research content.According to the histogram and cross-plot analysis in this paper, the feature and variation range of logging curves of Carboniferous and Permian Systern are quantitatively analyzed of in Hancheng area. The coal seam is low in natural gamma, density, p-wave velocity, p-impedance, shear wave velocity, shear wave impedance, Young's modulus and bulk modulus. The coal seam can be identified by one of these attributes. The sensitive parameters of coalbed gas content include density, p-impedance, shear wave impedance, MuRho, LamdaRho and ERho.Based on forward analysis of single well and multiple coal bed sets wedge model, coal-bearing beds are strong amplitude reflection. The coal seam thickness and dominant frequency of seismic data are the main influence factors of identifying coal seam by seismic data. The root mean square (RMS) amplitude increases with the coal thickness when it's more than 2m. So the RMS amplitude attribute can be used to predict coal seam thickness (more than 2m).The study of structure and fracture characteristics of top coal seam is the precondition of CBM enrichment area prediction. The coal seam fracture distribution and structure form is adopted by interpretation based on multiple attributes fine. Thickness of coal seam is the basis of CBM resource estimation and one of the important parameters in the evaluation of CBM enrichment region. The prediction precision of coal seam thickness is gradually improved by paleotopography, RMS amplitude attribute, post-stack impedance inversion and geo-statistical inversion. The growing degree of the coal seam fracture directly influences the coal seam permeability and the drainage rate of CBM. The prediction accuracy of coal seam fracture development area is improved by post-stack seismic attributes and pre-stack azimuth prediction method. According to the above techniques and methods applied in Hancheng 3D CBM survey, the seismic characterization technique of CBM reservoir is developed for structure (buried depth, form, fault and collapse column), spatial distribution and fracture development degree of CBM reservoirs.Coal-bed gas content is one of the important parameters in the evaluation of CBM enrichment area and it's difficult for prediction. According to the single and multiple parameters analysis, coal-bed gas content can be idenitified by density and p-sonic. AVO inversion and pre-stack simultaneous inversion are used to predict coal-bed gas content based on 3D seismic data. Poisson's ratio of AVO inversion is used to predict coal seam fracture development degree or permeability and it indirectly indicate the hydrocarbon content of coal seam. The density, p-sonic, p-impedance and LamdaRho volume are derived by pre-stack inversion. The distribution of coal-bed gas content is quantitatively predicated by the coal bed gas content multi-parameters fitting formula. The method is carried out for 5# and 11# coal seam in Hancheng 3D survey and 72.7% of the prediction matches the real drilling results of 11# coal seam.There're many factors of affecting CBM enrichment area. Four main controlling factors are optimized as evaluation standard of CBM enrichment area, including coal seam buried depth, thickness, the degree of fracture development and gas content. Making full use of four controlling factors maps of 5 and 11 coal seam in Hancheng 3D survey, CBM enrichment area is predicated. The prediction results are tested by late drilling results. It provides the basis for well development of CBM and CBM enrichment area prediction technique by comprehensive information is formed. The technique is carried out in 3D CBM survey of the southern BD area. The total area of ?+? class enrichment area of 4+5# coal seam is 62km2 and that of 8+9# coal seam is 34km2.32 development wells are deployed according to CBM enrichment area prediction results of 3D survey in the southern BD area. The gas breakthrough time of one development well is only 2 months and daily gas is 1348m3 until September 25,2014. As a result it improves the efficiency of the CBM exploration and development.Making full use of CBM 3D seismic data, we innovate in the integration of seismic characterization of CBM reservoir technique and get the fine characterization of coal seam structure, distribution and permeability. The coal-bed gas content is predicated by the combined parameters based on 3D seismic data for the first time. The distribution of coalbed gas content is analyzed and the prediction accuracy is improved. The CBM enrichment area prediction technique by comprehensive information is formed innovatively. The application of this technique can improve the efficiency of CBM exploration and development and it has a broad application prospect. |
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