Research On Coal Seam Compressibility Index And Evaluation Method

Coalbed methane(CBM)resources in China are very rich,and it is third in the world.It has great development value and huge exploitation potential.But in recent years,the effect of CBM development in China is far lower than expected.It mainly shows that the production of single well of CBM is low and the effect of CBM fracturing is poor.Therefore,the problem of CBM fracability is becoming increasingly prominent,which is an important problem to be solved urgently for CBM development and utilization.In this thesis,the fracability of CBM is studied.Basing on analyzing and preferring the parameters of CBM fracability,the index of CBM fracability is studied,and the method of evaluating the CBM fracability is formed by using this index.Through the research work of master's degree,the following results are obtained in this thesis:(1)On the basis of detailed literature research and deep analysis of parameters that can characterize fracability of coal seam,Shale content,Tensile strength of coal mass,Ash content,The type of coal petrology,and Water content are preferred to characterize the fracability of coal seam.(2)According to characterize the performance of CBM wells after fracturing,the production system of CBM wells was analyzed in detail.By comparing the coal seam gas production capacity of a variety of indicators,at last,the product of stable gas production and flowing bottom hole pressure were employed to characterize the performance of CBM wells.(3)Based on the planning theory,using the least squares principle and the single weight which determined by subjective weighting method,the model of the combination weights of parameters was established,and the fracability index of coal seam were determined too.(4)Based on the grey Euclid correlation model,the fracability index of coal seam were quantified,and the fracability are evaluated accordding the fracability index.On the basis of fracability index,an improved matter-element extension model is established to evaluate the fracability.By using the asymmetric degree of closeness to replace the maximum membership criterion,an improved matter-element extension model is established to evaluate fracability of the coal scam.(5)Combined with the evaluation methods of grey Euclid relation model and the non symmetric closeness degree matter-element model formation method,the synthetic evaluation of the coal seam is established to evaluate the of HC block.The application shows that the coincidence rate is high,and it can meet the engineering practice.