Cause analysis and preventive measures of cyclical fluctuation of coalbed methane production wells in Guqiao coalfield

The cyclical fluctuation phenomenon of the coalbed methane (CBM) production well is observed for the first time in Guqiao Coalfield. What causes this phenomenon and how prevents it,which have not been reported at home and abroad. The analysis of preventive measures and causes of cyclical fluctuation in coalbed methane wells production is of great significance for the efficient development of low permeability and soft broken seam. By the in-depth analysis of bottom hole pressure,the gas production and other production data of the coalbed methane wells,the cycle is divided into the stationary stage of production output (bottom hole flowing pressure),the declining stage of production output (bottom hole flowing pressure) and the increasing stage of production output ( bottom hole flowing pressure). Based on gas line gathering,data acquisition instrument and coal reservoir,combined with the coal reservoir characteristics,reservoir stimulation and work over,it shows that the gas resistance effect which leads to the solid effect is the main cause of the production cyclical fluctuation phenomenon. Cyclical fluctuation characteristics occur,as the consequence of the blockade to fluid (water and gas) flow caused by the gas resistance effect and the solid resistance effect,which is also verified by numerical simulation method. Some suggestions are put forward to reduce the air resistance and solid resistance effect,including using the coal seam roof fracturing instead of directly coal seam fracturing,optimizing sur- face active agent,adopting drainage technique of hierarchical control pressure,and producing properly coal fines of propped fracture,etc. .