关键词: 煤层气, 排采, 定体积法, 含气量, 反演

Abstract: The gas content of coal reservoir is one of the key factors affecting gas production, which cannot be achieved directly for most gas wells, and the gas content of low-rank coal measured by desorption method is not accurate. The purpose of this study is to determine the dynamic variation of gas content of the coal reservoir in the Dafosi coal field by synchronizing feedback of coalbed methane (CBM) well drainage and production data to coal reservoir parameter dynamics and by studying the real-time gas content inversion through “constant volume method” using the production data of CBM wells. The results show that (1) for multiple original gas contents, qA decreases linearly with time and the descending trends are the same. Also, the real-time gas content changes with the same linear slope: gas production and gas consumption are synchronized, regardless of the production time interval. (2) Analyzing different time steps of 1 d, 3 d, and 5 d, and setting original gas content of 2 m3/t, 3 m3/t, 4 m3/t, 5 m3/t, 6 m3/t, and 8 m3/t respectively, the real-time gas content change relationship of coal reservoir is highly consistent. It is considered that CBM wells follow the law of “constant volume” gas production, that is, there is no formation and expansion of pressure drop funnel.（3）In the continuous drainage stage, the real-time gas content decreases linearly with the drainage time. The linear reduction rates of real-time gas content in coal reservoirs are different before and after the interruption of drainage and production: 0.00546 and -0.00435, respectively; the slope of real-time gas content change in the second stage is smaller than that in the first stage, which is interpreted to result from coal powder that was produced in the process of drainage and mining, blocking the desorption of lump coal, causing reservoir damage and reducing the volume of coal seam to be desorbed.

Key words: coalbed methane, production, constant volume, gas content, inversion