Study On Comprehensive Evaluation Of Coal Reservoir Reconstructibility Based On Seismic-Geological Method

At present,research on the exploration and development of coalbed methane(CBM)primarily focuses on the prediction of favorable areas for coalbed methane enrichment and development.However,the key influencing factors and control mechanism of coal reservoir reconstructibility were still poorly understood.There is no systematic and multi-technical comprehensively characterization of fine characterization and comprehensive evaluation methods.The coalbed methane resources of high rank coal in China are abundant and have great potential.It is of great significance to reveal the key factors and internal mechanism that affect the reservoir reconstructibility for improving the exploration and development efficiency of coalbed methane and realizing the commercial development of coalbed methane.In this dissertation,Zhengzhuang area in the southern of Qinshui Basin was taken as the research area,and by a combination of multiple methods and techniques to quantitatively identify and finely characterize the factors that affect the coal reservoir reconstructibility.By analyzing and clarifying the influence of various factors on the propagation law of hydraulic fracturing fractures in the study area,the key factors were determined,and the evaluation method system of coal reservoir reconstructibility was established.Based on the reconstructability evaluation of Zhengzhuang area,an adaptive reconstruction scheme was proposed.The major observations and conclusions from this dissertation include:(1)A new method for quantitative identification of coal texture and prediction of distribution characteristics based on 3-D seismic curvature analysis was proposed,which can be used to quantitatively reveal the lateral distribution characteristics of coal texture based on a few exploration wells and certain seismic information.(2)The concept of regional adaptive residual strain index was proposed,and the in-situ stress prediction model was constructed,which revealed the characteristics of in-situ stress distribution in the Zhengzhuang area.Meanwhile,the extension law of hydraulic fracturing cracks under stress conditions was clarified.It is difficult for the coal seam crack,and limit the extension of cracks.The length of the main fractures in the study area tends to decrease as the average effective stress increases.The lower in-situ stress environment in the southwestern-northeastern area of Zhengzhuang is favorable for the cracking of hydraulic fractures,and the effect of fracturing is better.While,in the northwestern-southeastern regions(the high stress area),the fracturing effect is relatively poor.(3)The interaction mechanism among the tectonic curvature,coal lithotype,mechanical properties of coal seam and its roof/floor,and coal reservoir reconstructibility was finely characterized and clarified.The "four elements" of coal texture,in-situ stress,coal lithotype and structural curvature can be used as the key indexes for the evaluation of coal reservoir reconstructibility.The critical value of each index,the corresponding characteristics and evaluation grade of the indicated reservoir were established,and the reconstructibility evaluation standard and index system of No.3 coal reservoir in Zhengzhuang area were established.(4)A systematic evaluation method system of coal reservoir reconstructibility was established,and a quantitative comprehensive evaluation of coal reservoir reconstructibility in Zhengzhuang area was carried out.The matching relationship between the reconstructibility zoning of coal reservoir and the fracturing/draining of CBM wells was analyzed systematically,and the adaptive yield improvement scheme of different types of modifiable reservoirs was proposed.