Study On The Process Of Drainage And Gas Extraction For Multilevel Pressure Drop Of CBM Well

The coal-bed methane(CBM)resources in China are abundant,but the average production of CBM wells is pretty low.The reasonable drainage scheme can alleviate the damage of coal reservoir during the drainage process,and is also an important safeguard measure to obtain high production and stable production of CBM wells.In this thesis,based on the literature research and analysis of actual drainage data,we have improved the multi-stage pressure drop drainage technology,which is based on progressive reduction of bottom hole flow pressure,and developed the optimal pressure drop control scheme for the target CBM wells.In order to investigating the theory and process of coal-bed methane wells drainage,in this paper,based on the geological and production data of the target area,the threedimensional geological modeling and numerical simulation methods are used to analyze the dynamic data of target wells,complete the history matching task,investigate the reservoir pressure expansion dynamics in the condition of different Porosity,permeability,reservoir thickness,well spacing,drainage rate,drainage time,and bottom hole flow pressure,and Analyze the impact of various factors on pressure drop propagation.The result show that,when value of the porosity is low,the permeability is low,the reservoir thickness is thin,the spacing between the wells is narrow,the drainage rate is larger,the drainage time is longer and the bottom hole flow pressure is lower,the pressure-reduction funnel is more conducive to the propagate in the reservoir..Considering the specific characteristics of various stages in CBM well drainage process,a multi-level pressure drop drainage technology and technical scheme for CBM wells are proposed and simulated.The simulation results show that,within a certain limit,the faster the downhole pressure is reduced,the more prominent the effect of enhanced recovery is.But with the speed of pressure drop increases,the growing rate of increase in production alleviate.At this time,it is not advisable to further reduce the pressure to achive high gas production.On the basis of pressure drop optimization of single well,the paper proposed a technical scheme under the conditions of scale development.