Abstract:
Compared with middle and high rank CBM, low rank CBM is more advantageous with low coalification of coal rocks, low gas content, high ash content and good reservoir physical properties.The selection of low rank CBM blocks is of great significance to decrease CBM development cost and promote the development of CBM industry.The low rank CBM block in eastern Australia was taken as the study object.According to the multi-level fuzzy mathematical thinking, combined with the characteristics of low rank CBM in this block, cumulative thickness, gas content, ash content, recoverable reserves, porosity, permeability, gas saturation, critical desorption ratio and original formation pressure are selected as the evaluation indexes to establish the multi-level fuzzy model for evaluating the development results of low rank CBM.Then, based on the weight coefficient of evaluation index and the 3D geologic model of this block, development result evaluation parameters of low rank CBM are constituted.The thresholds of development result evaluation parameters of this block are determined as 0.507 and 0.317 by taking the average daily gas production in the stable period of 30×10
3 m
3 and 6×10
3 m
3 as the yardstick, and accordingly the favorable development areas in the this block were determined.Thus, multi-level fuzzy evaluation model is successfully applied to the selection of favorable development areas in low rank CBM blocks.In the actual application, the single-well gas production of developed wells in high, middle and low yield zones are highly accordance with the selection results.And it is indicated that multi-level fuzzy evaluation plays a guiding role in selecting the favorable blocks of low rank CBM.