| As an important basic work,the evaluation and optimization of favorable blocks directly determine the success or failure of CBM development.In this paper,Laochang mining area is the research object which has the characteristics of high insitu stress,multi coal seam and complex coal structure conditions.Through the characteristics of coal strata,gas content and reservoir reconstruction,find out the favorable distribution of CBM geological conditions,put forward the sweet spots index and optimization model which is suitable to the study area,optimize the surface and vertical sweet spots,establish a appropriate technical system for multi coal seam gas exploration and development and provide support for the exploration and development of coalbed methane engineering.Coal seam structure of Laocahng mining area is relatively simple,No.3,No.7+8,No.9,No.13,No.16,No.19 coal seam are stable,the thickness,structure,layer spacing varies greatly.The coal structure is obviously affected by the tectonic action.The proportion of I + II of No.13 coal seam is the lowest,and the ratio of No.16 coal is the highest,which shows that the No.16 coal seam has good transformation and permeability.The main coal seam gas content showed the northeast and Southeast high and low in the west,the change trend of shallow low deep high coal seam gas content,the contour is roughly consistent with the buried depth contour,shows that the typical characteristics of gas-anticline anticline gas bearing is often poor,but the gas bearing in the direction of the flanks and the dip direction is better.The Laochang mining area has the characteristics of high in-situ stress,with the characteristics of high ground stress,the stress state is mainly represented by the dynamic field type,and there is a good linear relationship between the stress and the depth.The structure complexity can be characterized by the similar fractal dimension.The dimension indicates that the Yuwang block and the upper part of Daobanfang block locates in simple structure zone,and the corresponding fractal dimension is minimum;the larger fractal dimension is mainly distributed in the northwest and southern of Daobanfang block and in the northwest,northeast of the outside of the Yuwang block,the corresponding fractal dimension is large,the largest regional fractal is more than 1.5.The structural curvature has a good correlation with permeability,gas bearing and stress state of coal reservoir in the Laochang mining area.According to the analysis,it is concluded that the reservoir permeability is relatively good in the range of-12.5 × 10-512.5 × 10-5,and the permeability is obviously worse when the structural curvature is larger than 12.5×10-5 and less than-12.5×10-5.The minimum horizontal principal stress and the maximum horizontal principal stress increase with the increase of the absolute value of the structural curvature when the structural curvature value is less than-10×10-5 and largeer than 10×10-5.It can be inferred that the stress in the study area has a tendency to increase with the increase of the structural curvature,and the stress field is relatively low in the range of-1010×10-5.Reference to the classical theory with the key elements of hierarchical optimization method,step by step from the key factors gradually to the target area selection,combined with the actual situation of the study area,select the coal seam depth,cumulative thickness,cumulative gas content,structural characteristics,stress,topography as a index,selected dessert,and graded as class I and class II and class III.Due to the comprehensive analysis of coal,gas,mining,reservoir reconstruction characteristics,combined with the research results and the idea of joint drainage,propose the coal seam spacing,permeability,coal structure,reservoir pressure gradient,critical desorption pressure,coal and rock mechanics for sweet spots evaluation system index.After layer by layer optimization,No.16,No.19 is the most favorable layer,No.7+8 is the favorable layer,No.3,No.9,No.13 are the unfavorable layer. |
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