Production Characteristics And Influencing Factors Of Combined Production Wells For Medium To Low-rank Coalbed Methane In Tiefa Mining Area

The thesis selected 30 coalbed methane(CBM)wells in Daxing Mine of Tiefa mining area as the research object.The productivity characteristics of CBM wells in the study area were analyzed.The mechanism of CBM well productivity difference control was clarified.The influence of the superimposed gas-bearing system on the productivity of CBM combined wells was discussed.The main conclusions are as follows:CBM wells in the study area can be divided into high-yield gas wells,mediumyield gas wells,low-yield gas wells,and very low-yield gas wells according to their productivity.The productivity of CBM wells shows obvious regional differences.High and medium production gas wells are mainly distributed in high production areas.Lowyield zone 1 and low-yield zone 2 are mainly distributed with low-yield gas wells and very low-yield gas wells.The gas production of high-yield gas wells is positively correlated with the average daily water production,while the gas production of medium and low-production gas wells has a relatively poor correlation with the average daily water production.The effect of combined production in different stages of CBM wells varies greatly.The control mechanism of the regional productivity difference in the study area and the productivity difference between wells in the high-yield is classified.The regional productivity difference of CBM wells in the study area is mainly controlled by structure.The reservoirs in the high-yield area located in the secondary anticline have strong seepage capacity,and coalbed methane wells have high gas and water production rate.The reservoirs in the low-yield zone 1 and the low-yield zone 2 located in the syncline control zone have weak seepage capacity and weak gas production capacity of coalbed methane wells,the water production capacity is also lower than that of coalbed methane wells in high-yield areas at the same stage.The productivity difference of CBM wells in high-yield areas is also affected by the structure.CBM wells near the core of anticlines and faults have relatively high gas-water production capacity.Casing pressure and discontinuity in drainage may also cause gas and water production differences between CBM wells in high-yield areas.Casing pressure has a controlling effect on maintaining the high and stable production of CBM wells.In the stage of pressure control and stable production,after the casing pressure of CBM wells in the study area is lower than 0.4MPa,the daily gas production has a significant downward trend due to the pressure sensitivity effect.Intermittent drainage will result in a decrease in the daily gas production of coalbed methane,but the percentage reduction in gas production of coal gas wells caused by intermittent drainage is extremely high.According to the characteristics of sequence stratigraphy,gas content and rock sealing,the coal-bearing strata in the study area are divided into four independent gasbearing systems,in which the upper coal group is a unified gas-bearing system,and the lower coal group is a three-set superimposed gas-bearing system.Through the analysis of the compatibility of the combined production layer,the influence of the superimposed gas bearing system on the production capacity of the combined production well in the study area is discussed.The gas production of the combined production well from high to low is : upper coal combined mining,upper and lower coal combined mining,lower coal combined mining.The CBM well combined with upper and lower coal groups is vertically interfered by gas-bearing systems,and the gas production potential of some reservoirs is suppressed.This article is about 47,000 words,including 51 illustrations,23 tables and 122 references.