Numerical Simulation Of Factors Affecting Coalbed Methane Production Capacity In Laochang Mining Area

The coalbed methane reserves in the Laochang mining area in eastern Yunnan are high,but due to the large number of thin coal seams,the complex coal structure and limited reservoir reforming effects,the development of coalbed methane is still in the pilot test stage.Based on the analysis of coalbed methane geological data in exploratory wells / parameter wells,this paper refines the coalbed methane geological model,conducts a numerical simulation study of coalbed methane for multiple and thin coal seams,complex coal structures,and communicating aquifers to characterize the dynamic changes of reservoir parameters and provide reasonable development recommendations.The main achievements are as follows:(1)Class Ⅲ coal body structure coal(mylon coal)is generally developed in the single coal seam in the area.The gas content of the coal reservoir is considerable,but the saturation is low.The coal seam is mostly sand and mudstone roof and baseplate.The current pilot test wells output is not high.(2)Under the condition that the total thickness of the coal seam is constant,the cumulative gas production and the cumulative water production both increase with the increase of the proportion of the primary structure coal within 6000 days of simulating the combined mining of the primary structure coal and mylon coal.The primary structure coal is superior to the Mylon coal seam in terms of original permeability,reservoir damage recovery,and pressure transmission.However,the Mylon coal seam also desorbs and supply the gas after the primary structure coal seam is greatly depressurized.Therefore,in the later stage of drainage,there is a phenomenon that the daily gas production of the high Mylon coal seam reservoir is greater than that of the high primary coal seam.The simulation results also indicate that the thickness of mylon coal cannot be too high,otherwise it will affect the economy of the gas well.However,when the thickness of the primary structure layer is similar,a certain thickness of mylon coal can increase the stable production period.(3)For coal seams with fracturing connected to the aquifer,during the 3,000-day simulation period,with the increase of the daily discharge in the early stage of drainage,the cumulative gas production increases first and then decreases.Properly increasing the daily discharge can increase the rate of depressurization and Gas production efficiency,but too fast drainage will cause damage to the reservoir permeability,resulting in a situation where the production capacity does not rise but decline;as the aquifer permeability increases,the highest gas production comes later,but the duration of high production is longer.As a result,the cumulative gas production and water production will eventually increase.In the early stage of drainage,due to the rapid flow of water from the high-permeability aquifer,the drainage rate in the coal reservoir is suppressed,which avoids the speed-sensitive and pressure-sensitive effects caused by excessively rapid drainage and depressurization in the vicinity of the well area,and increases the pressure drop funnel The extended range is conducive to more gas desorption and discharge.(4)For the adjacent two-layer coal reservoir with the same geological conditions except permeability,the cumulative gas production of different permeability differential co-production during the 6000-day simulation period is better than that of the sum of two single-layer coal mining,The closer the permeability,the more significant the effect.Compared with single wells,combined production can avoid the reservoir damage caused by excessive drainage at the initial stage of low permeability reservoirs,shorten the drainage time and improve the recovery rate.