Quantitative Characterization Of Coal Rock Strength And Fracturing Adaptability Research

Hydraulic fracturing has been routinely used in stimulating production from coalbed methane in china,numerous papers have been published on the theory and technical method about fracturing in coalbed.But the effect of fracturing in the so called "hard" coal seam can be very different from that in the "soft" coal seam,when fracturing the "hard" coal seam,elastic deformation occurs,and fractures with high fracture conductivity were formed;when fracturing the "soft" coal seam,plastic deformation occurs,and the preformence of CBM wells are comparatively worse.So how to quantitatively describe the "hardness" or "softness"property of coal mass,and how to quantitatively describe the adaptability of the fracturing technique to coal seam with different strength are two key questions need to be solved.Based on the optimization of parameters that can characterize the strength of coal mass and the accurate evaluation of the production of CBM wells,the quantitative characterisation for the strength of coal and the adaptability of the fracturing technique to coal seam with different strength were studied in this dissertation.Followings are the research findings obtained during the past two years.(1)On the basis of detailed literature research and deep analysis of parameters that can characterize the strength of coal mass,shale content,tensile strength of coal mass,water content and the type of coal petrology were selected to characterize the strength of coal mass.The calculation method of the four parameters were also determined.(2)In order to characterize the performance of CBM wells after fracturing,the production system of CBM wells was analysed in detail,multiple parameters was tested,at last,the product of stable gas production and flowing bottom hole pressure were employed to characterize the performance of CBM wells.(3)The fuzzy comprehensive evaluation was employed to predict the productivity after fracturing.the different performance of CBM wells form the remark set,the factor set contains shale content,tensile strength of coal mass,water content and the type of coal petrology,the weight of each factor was determined by fuzzy analytic hierarchy process.The applications show the accuracy of evaluation can satisfy the engineering requirement.(4)Based on the evaluation vector,the quantitative coal mass strength index was first introduced in this thesis,the index is closely related to the performance of CBM wells after fracturing,it can characterize the strength of coal mass as well as the productivity of CBM wells,besides,the calculation of the index is simple.(5)Based on the coal mass strength index,a lot of field application work were conducted to verify the validity of the index.the adaptability of the fracturing technique to coal seam with different strength was first confirmed,these findings are of great significance for coalbed methane fracturing and recovery...