Method for predicting extraction productivity of underground coal-seam gas

Abstract

The invention provides a method for predicting extraction productivity of underground coal-seam gas, in which the actual change of permeability of a coal seam is considered and the extraction productivity of extraction drilling group can be predicted. The method comprises the following steps: 1) measuring original parameters of the coal seam to be measured; and 2) by calculating a model provided by the invention, acquiring the mean permeability after the extraction, the coal-seam gas pressure after the extraction, the coal-seam gas average content after the extraction and the coal-seam gas extraction quantity. In the method for predicting the extraction productivity of the underground coal-seam gas, based on Darcy's law of seepage, a mathematical model for predicting the extraction productivity of the underground coal-seam gas based on the permeability variation in the extraction process is established; and because the actual change of the permeability in the extraction process is considered in the mathematical model, the seepage situation of the coal-seam gas can be correctly reflected. In the further calculation step, the mathematical model is calculated by adopting a differencediscrete method, the convergence rate is high, the precision is high, the stability is high and the calculation accuracy and speed are improved.

Description

technical field [0001] The invention relates to the technical field of coal gas exploitation, in particular to a method for predicting production capacity of underground coalbed methane extraction. Background technique [0002] Coalbed methane, that is, coal mine gas exists in the coal seam in an adsorbed state or a free state. Usually, the amount of gas in the adsorbed state accounts for more than 90%, and the amount of gas in the free state accounts for about 10%. When the coal seam is mined, the gas existing in the coal seam is continuously released with the disturbance of the coal seam mining, resulting in gas explosion, coal and gas outburst, gas suffocation and other hazards. Drainage of underground coalbed methane is not only an effective method for controlling coal mine gas disasters, but also an indispensable way for the development of coalbed methane resources. [0003] The prediction of underground coalbed methane production capacity can guide the orderly develop...

AI Technical Summary

Problems solved by technology

[0004] The current downhole coalbed methane productivity prediction method has many defects, such as the following aspects: only for the single-hole coalbed methane extraction volume, but cannot predict the productivity of the drainage drilling group (group); the coalbed methane drainage model is established In the case that the permeability is constant during the extraction process, but according to the actual production on site, the permeability of the coal seam is constantly changing during the extraction process, and none of the existing models can meet the actual production

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