The Determination of Casing Releasing Pressure of CBM Wells and Its Application

In the stage of stable production and production increase of coalbed methane wells, it is necessary to determine the reasonable casing releasing pressure to obtain stable air supply. Based on the threshold pressure of coal reservoir, seepage theory, CBM development geology theory etc., a mathematic model of releasing pressure for CBM wells was established. From CBM exploration and development data of Daning Block, Qinshui Basin, the accuracy of the mathematic model was verified. The relations between casing pressure drop and average daily gas production were analyzed. When predicted pressure from this model was in good agreement with that applied in field data, gas production of CBM Wells would be higher. When the pressure difference was within 0.15 MPa, the average daily gas production of CBM wells could be more than 1 000 m3/d in stable production stage. When the pressure difference was more than 0.15 MPa, daily gas production would be stabilized at lower gas production rate. The results showed that daily gas production is reduced in power function with casing pressure drop and the mathematical model of casing releasing pressure in coal bed methane well can provide theoretical basis for CBM wells production.