Abstract:

In order to further study the reasonable production allocation and drainage control method, and extend the high and stable production period of CBM wells, the reasonable production allocation is proposed by comparative researches on the isothermal adsorption of coal bed and production parameter of CBM wells in South Yanchuan CBM field. On the basis of the comparative analysis of the parameters and dynamic regulation of coalbed methane drainage on site, and taking coal reservoir pressure, critical desorption pressure, Langmuir pressure and stable production pressure as the key control nodes, the drainage process of CBM wells can be divided into five stages, and then the method of production parameter control during every drainage stage is studied. The result shows that the gas yield peak appears when the bottom hole flowing pressure is at about Langmuir pressure of coal bed in South Yanchuan CBM field. There is a good linear relation between the stable gas production and the peak gas production, as well as that between the stable flowing pressure and the Langmuir pressure. The fitting formula can be used to calculate the reasonable stable flowing pressure and stable yield of each well. The above five stages are fast drainage stage, slowly pressure drop drainage stage, gas yield rising stage, gas yield fluctuation stage, and stable yield stage. For the South Yanchuan CBM field, the reasonable bottom hole flowing pressure drop is about 0.1 MPa/d during the fast drainage stage. The drainage control at slowly pressure drop drainage stage, gas yield rising stage, and gas yield fluctuation stage are very important. The bottom hole flowing pressure drop should be about 0.003 MPa/d during the slowly pressure drop drainage stage, less than 0.005 MPa/d during the gas yield rising stage in Tanping structural belt, less than 0.01 MPa/d in Wanbaoshan structural belt, and about 0.003 MPa/d during the gas yield fluctuation stage.

Key words: South Yanchuan CBM field, CBM, reasonable production allocation, bottom hole flowing pressure, drainage stage, production parameter control