Drainage Damage Mechanism And Process Optimization Of Coalbed Gas Wells

The coalbed methane resource is 36.8×10~122 m~3 in the depth above 2000m in China,ranking third in the world.By the end of 2013,the proven geological reserves were5,654×10~8m~3.At the end of the"Twelfth Five-Year Plan",the designed annual production of coalbed methane fields in China has reached 100×10~8m~3,but the actual annual production is only 44×10~8m~3.According to statistics,at present,only 30%of16,000 CBM wells in China are in normal production,and a large number of CBM wells are destined to become negative assets corporate on the first day of production.And the main cause of low production in most CBM wells is the use of unreasonable drainage technologies.Therefore,it is of great significance to study the drainage technology of CBM wells to guide the effective development of CBM.Firstly,this paper investigates and analyzes the mechanism of the occurrence and gas production of coal reservoirs,and combines the production data of CBM wells to propose that supporting fracture conductivity and reservoir permeability damage are the main reasons for the low production of CBM wells.Secondly,the LD-1A conductivity tester was used to simulate the sedimentary features and migration laws of pulverized coal under different drainage regimes,and the damage degree of pulverized coal to the fracture conductivity in different modes was compared.Based on the sediment kinematics theory,the critical starting flow rate and pressure difference of free pulverized coal particles in the fractures of reservoir support are studied,and the constant pressure control powder drainage technology of CBM wells is improved.Finally,the permeability change model was derived based on the MATCHSTICK model,combined with the actual production process of CBM wells,a dynamic prediction model for reservoir permeability in different drainage stages was established.The production data was used as an example to calculate the reservoir damage rate in different drainage stages,combined with drainage control principles to optimize the working regime of CBM wells and provide reference for the development of CBM wells.