The Exploitation On The Feasibility Of Commingled Production For Coalbed Methane

The commingled production is usually used in an area abundant in coal.The reasons may include but not limited to the thickness of a single coal bed is quite thin,the economic benefit of exploiting a thin layer mining is low,and the technique can reduce the overall cost of coal seam gas well development and improve the economic benefit of the coalbed gas field.However,in the actual development process,the coalbed gas production capacity is lower than the sum of single layer production,and the effect of commingled production is not obvious.Therefore,it is of great significance to study the feasibility of multilayered reservoir commingled production.Based on the reservoir characteristics of a block and the production data of the CBM well in study area,this paper analyses the productivity characteristics of commingled production in this area and completed historical matching for the typical developed well.Through the establishment of the numerical simulation model of commingled production,By using single factor method and orthogonal test method,the key factors that restrict the commingled production are analyzed,and the suitable reservoir geological conditions are obtained.The feasibility of multi reservoir combined mining is discussed by means of gas reservoir engineering.The results showed that: The production capacity is larger in the study area.The difference of pressure gradient between reservoirs only affects the duration of drainage and decompression stage,and has little influence on the capacity of commingled production.Permeability,interval spacing,critical desorption pressure and Lanshi volume are the key factors restricting the commingled production.These factors rank the influence degree of commingling production from large to small is listed as follows:the permeability difference between different coal beds,the interval between layers,the difference of critical desorption pressure and the difference of the Langmuir volume..In order to obtain larger production capacity,the following reservoir conditions should be satisfied: the ratio of permeability of two layers should be less than 5,the interval of layer should be less than 100 m,and the difference of critical desorption pressure should be less than 0.6MPa,and the Langmuir pressure of the lower coal bed should be slightly larger than that of the upper coal seam.The main reason is the mismatch of reservoir permeability and the expansion of pressure drop funnel.Based on the above research,we summarize the principles of the selection of layers and guide the production practice.