Analysis on the relationship between pressure drop laws and production parameters of CBM well: A case study on the Baode Block

The production systems of coalbed methane (CBM) blocks are mainly based on field experience but less on the geological conditions and development status of the blocks. The extension form of pressure drop funnel is the specific manifestation of the geological characteristics and development mode of CBM well, so formulating a rational production system based on pressure drop laws is the key link for the scientific development of CBM fields. The ratio of the lateral pressure drop radius to the vertical pressure drop value of pressure drop funnel is defined as the representation coefficient of pressure drop funnel. It is deemed that the higher the representation coefficient of pressure drop funnel is, the higher the single-well CBM production is. The pilot area of Baode Block was taken as an example. The effects of three coalbed permeabilities, groundwater fluid potential and interference between well groups of pilot area on the representation coefficient of pressure drop funnel were analyzed by virtue of Eclipse modeling and Matlab drawing toolbox. Then, the functional relation between production parameters (reasonable casing releasing pressure and reasonable pressure drop rate) and the representation coefficient of pressure drop funnel was established. Finally, the reasonable casing releasing pressure of Well C1-C13 in the progressive development area and the reasonable pressure drop rate of Well S1-S12 were calculated. It is shown that the smaller the differences between the theoretically calculated production parameters and the actual values of a well are, the higher its single-well CBM production is. That the proposed CBM production parameter calculating method is reliable and can provide the guidance for the rational production of wells with casing pressure but no gas releasing and those with gas breakthrough, as well as the theoretical basis for the quantitative production of CBM blocks.