Interlayer Interference Mechanism Of Superposed Gas-bearing System Coalbed Methane Production And Its Application

Coalbed methane(CBM)refers to the hydrocarbon gas mainly methane in coal seams and coal-measure strata.The efficient development and utilization of CBM is of great significance to ensure coal mine production safety,alleviate the contradiction between energy supply and demand,and reduce greenhouse gas emissions.The eastern Yunnan Province and western Guizhou Province region,as an important CBM resource storage areas in southern China,is rich in CBM resource.However,due to the geological characteristics of CBM in this area,conventional CBM production methods cannot be fully applied,and the inter-layer interference phenomenon reduces the efficiency of CBM production.This article was based on the development characteristics of multiple coal seams,referred to the theory of pressure relief for outburst coal seam mining,and used the interlayer interference of CBM production in the superimposed gas-bearing system independently developed by Chongqing University.Using this physical simulation apparatus has carried out a series of test under the conditions of different reservoir depths,different reservoir spacings and different combined production layers.The evolution law of reservoir parameters and the interlayer interference phenomenon and its formation mechanism in the process of CBM production in the superimposed gas-bearing system were systematically analyzed,and the influence of reservoir occurrence characteristics on interlayer interference was explored.A calculation method of interlayer interference factor was proposed,and on this basis,a mathematical model of CBM migration in a superimposed gas-bearing system considering the inter-layer interference effect was established,and the linkage relationship between reservoir pressure-gas-bearing property-permeability in CBM production in superimposed gas-bearing system was preliminarily discussed.Through the above research,the main conclusions of the research are as follows:(1)Based on the physical simulation test of interference between CBM production layers in the superimposed gas-bearing system,the reservoir pressure,reservoir temperature and reservoir deformation evolution law of each coal seam in the superimposed gas-bearing system CBM production process were analyzed,and the drainaged layer and adjacent layers were compared.Compared the evolution law of reservoir parameters between drainaged layer and adjacent layers,the phenomenon of interlayer interference and its formation mechanism were revealed.The results showed that in the process of CBM production,under the combined action of the pressure difference between the layers and the deformation of drainaged layer,the undrainaged adjacent layers happened reservoir pressure drop,reservoir temperature drop,and reservoir deformation shrinkage.The dynamic response of the adjacent layers were regarded as interlayer interference phenomenon.(2)Based on the physical simulation test of interlayer interference in CBM production in the superimposed gas-bearing system,the influence of reservoir occurrence characteristics on interlayer interference was analyzed.The results showed that there were many factors affecting interlayer interference.The interlayer interference had a good positive linear correlation with the depth of the reservoir and the number of combined production layers,and the relationship with the reservoir spacing and adjacent layers had a good negative linear correlation.(3)Based on the fitting of the relationship between the interlayer interference and each single influencing factor,and the "normalization" processing mathematical method,a layer that comprehensively considers the relationship between the buried depth of the reservoir,the interval of the reservoir,the number of combined production layers and the relationship between adjacent layers was established.A comprehensive calculation formula for interlayer interference factor,and by applying the interlayer interference factor to a single coalbed methane migration model,a mathematical model of CBM migration in a superimposed gas-bearing system considering the interlayer interference effect was established.The model was embedded in the COMSOL Multiphysics software.Put forward a numerical simulation analysis method of CBM production in a superposed gas-bearing system considering the effect of inter-layer interference.(4)Based on the data of LC-S2 well,and using the proposed numerical simulation analysis method of CBM production in the superimposed gas-bearing system considering the interlayer interference effect,the analysis of the physical parameters of different reservoirs on the superposed gas-bearing system.Numerical simulation research on the influence of CBM combined production has preliminarily discussed the linkage relationship between reservoir pressure-gas-bearing property-permeability in CBM production in superimposed gas-bearing systems.