Production Mechanism Of The Coalbed Methane And Yield Improvement In The Dafosi Coal Field

During the production of DFS-C02 of coalbed methane well,Roadway tunneling of 40202 working face in Dafosi coal mine field truncated horizontal branches L3 and L5 of coalbed methane well DFS-C02,and subsequently closed off the horizontal branches.After the cutting of 40202 working face and the advance of coal mining working face,the daily gas production of the well appeared the phenomenon of not decreasing but increasing.By summarizing and analyzing the previous research results on the stress distribution law of surrounding rock in the working face,the pressure release hypothesis and stress model of seesaw are established.According to the seesaw stress model,During the advance of 40202 working face of Dafosi coal mine field,the overlying strata in goaf of the working face act on the overlying strata which is connected with it continuously of 4#coal,it creates the seesaw effect and forms a pressure relief zone in a certain area of the advancing direction of the working face,The pressure relief zone and the original depression-relief funnel in dfs-c02 well formed an interwell like interference effect.It enlarges the control area of the well,increases the pressure relief area,and increases the daily gas production of the well.According to the summation and analysis of the drainage practice of coalbed methane well in Dafosi coal mine field,It is found that when the flowing bottomhole pressure of most coalbed methane Wells in Dafosi coal mine field is about 0.7Mpa,the daily gas production of single well starts to increase substantially and continuously,Moreover,the bottom hole flow pressure value is inconsistent with the critical analytic pressure value calculated by Langmuir equation and the critical analytic pressure value calculated by submergence at the beginnning of gas production.Based on the analysis of Henry's law and the theory of adsorption heat,the model of "desorption-cavitation-mass transfer" coalbed methane production process based on the microporous unit was established.According to the analysis of this model,the production of methane of coal bed methane not only overcomes the energy problem,but also needs to overcome the resistance of micro-pore throat water,"Desorption-cavitation-mass transfer" is a process to overcome the resistance of pore-throat water;when pore-throat water is exhausted,methane of coalbed methane production from in the micropores conforms to Langmuir theory,at this time,the daily gas production of coalbed methane well in Dafosi coal mine field start to increase substantially and continuously,ln other words,the characteristic phenomenon required for exhausted of water of micro pore throat in coal reservoir in daofosi well field is that the flowing bottomhole pressure of CBM well is about 0.7Mpa.In order to improve the scientific and elaborate gas drainage of coalbed methane Wells in Dafosi coal mine field,at the same time,the gas drainage stage of coalbed methane well in Dafosi coal mine field is divided into the following stages:drainage and depressurization stage,"desorption-cavitation-mass transfer" stage,Langmuir stable production stage and Langmuir failure stage.By analyzing the pressure drop transfer process and the process of"desorption-cavitation-mass transfer",the process of "desorption-cavitation-mass transfer" is involved in all processes of gas production.