Study on drainage rate adaptation of deep CBM wells in South Yanchuan Block

In order to study the drainage management effect on the productivity of deep coal bed methane well, according to its dynamic characteristics, the production process could be divided into four stages, namedly water drainage, controlling casing pressure, reducing pressure for production increase and stable gas production. The author then came to the conclusion on the influence of pressure drop rate of water drainage and reducing pressure for production increase stage on the productivity through normalized data analyse. The research results indicated that the purpose of water drainage stage was to dredge the formation, and to expand the coal seam area of pressure reduction. It was neither conducive for the gas production if the daily level dropped too fast or too slow, and the speed should remain at 1.0～1.5 m, which could not only carry coal to the wellbore, but also could avoid coal seam permeability sharply decline as a result of sensitive stress response. In the gas production stage, the gas production rate increased and the liquid production rate decreased gradually. The lower the daily level dropped, the more conducive for the stable production in the coming days. The daily drop level should be controlled within 1.0 m, and the stable production in the later stage was from 1 000 to 1 200 m3/d.