Method of gas recovery by water drainage for high-coal-rank coal-bed methane well

Abstract

This invention discloses a method of gas recovery by water drainage for high-coal-rank coal-bed methane well, which is applied in the technical field of gas recovery of coal-bed methane well; the method disclosed by this invention comprises a water draining stage, a pressure building stage, a pressure controlling stage, a stable yield and high yield stage and an attenuation stage, wherein different stages have different pressure controlling demands; the dropping speed of a working fluid level of the coal-bed methane well is controlled within 5-7m / d at the water draining stage; underground flow pressure is stabilized at the pressure building stage; the working fluid level is dropped by 0-3m / d in each day; fluctuation of the underground flow pressure is controlled within 0-0.3MPa; air discharging quantity is increased to 200-300m<3> at the pressure controlling stage; the height of the underground working fluid level is kept 15-30m above a coal layer roof board at the stable yield stage; the pressure values of surface casing pressure and the underground flow pressure are within 0.101-0.11MPa at the attenuation stage; and at the attenuation stage, all sleeve pipe gates are opened or an intermittent draw-off type gas recovery procedure is performed by a downward draw-off pump. The method disclosed by this invention has the advantages that underground pressure is controlled so as to realize stable dropping of stratum pressure and the matching of the stratum pressure and desorption pressure, desorption range is enlarged effectively, and area depressurization is realized.

Description

technical field [0001] The invention relates to the technical field of coalbed methane well gas recovery, in particular to a method for drainage and gas recovery of high coal rank coalbed gas wells. Background technique [0002] At present, foreign coalbed methane production areas are mainly located in the middle and low coal rank basins with simple structure, while the central region with relatively stable structure in my country is dominated by medium and high rank coal. The high rank coal is: in the international coal seam coal classification, Coal with an average random reflectance of not less than 2.0%. my country's high-rank coal resources account for more than 60%, but the coal seam permeability is low, and it is a restricted area for exploration and development in the United States and other countries. Foreign coalbed methane drainage techniques suitable for medium and low coal ranks cannot effectively guide my country's high coal rank coal seams Gas extraction. [0...

AI Technical Summary

Problems solved by technology

my country's high-rank coal resources account for more than 60%, but the coal seam permeability is low, and it is a restricted area for exploration and development in the United States and other countries. Foreign coalbed methane drainage techniques suitable for medium and low coal ranks cannot effectively guide my country's high coal rank coal seams Gas extraction

[0003] The development of high coal-rank CBM wells in the Qinshui Basin is mainly based on vertical wells and horizontal wells. In the early stage of development, the drainage and production are mostly based on the curves simulated by laboratory values ​​and the high-porosity and high-permeability middle-low-rank CBM reservoirs such as Powder River and Black Warrior in the United States. Guided by the law of gas production, and due to unclear understanding of the dynamic change law of coal seam physical properties and drainage mechanism, in order to pursue early gas production and rapid production, the same and too fast pressure drop rate was adopted in different drainage stages, resulting in effective well around the well. The stress increases, causing serious and permanent damage to the coal reservoir, which eventually leads to low gas production of a large number of wells, and the production shows a trend of rapid decline

Images