Mechanism Of Interlayer Interference And Identification Model Of Interference Degree In CMB Coproduction

The occurrence characteristics and spatial discretization of multiple and thin coal seams in multiple coal seam area determine that the commingled production is the most effective way for economic development of coalbed methane(CBM)in these areas.However,the heterogeneity and its matching problem between layers of coproduction reservoir with great physical property difference lead to significant interlayer interference and poor productivity.With regards to this problem,the coal seams and CBM coproduction wells of Yuwang block of Laochang mining area in eastern Yunnan were selected as the research object.Based on the exploration data,well logging data,production data and experimental data,the geological conditions of multi-layer CBM coproduction in the study area were analyzed,and the phase stage differences between coproduction and single layer drainage were discussed.Combined with numerical simulation and physical simulation,the main controlling geological factors and their mechanism of interlayer interference were revealed.The model of interlayer interference degree was constructed,and quantitative identification of reservoir interlayer interference degree was carried out.It is expected to provide theoretical basis for reducing interlayer interference and achieving the goal of increasing production in the process of CBM coproduction.The main achievements and understandings are as follows:(1)The performance characteristics and influencing factors of interlayer interference in different drainage stages of CBM coproduction wells are revealed.A new understanding of the definition of interlayer interference is proposed.Based on the geological conditions of CBM coproduction and reservoir heterogeneity characteristics,the differences between coproduction and single layer drainage are clarified.Combined with the present situation of CBM development,the drainage stages of CBM wells in the study area are divided into drainage stage and sensitive desorption stage(some wells have rapid desorption stage).Combined with numerical simulation and production data,the sensitivity of key reservoir parameters to coproduction capacity is analyzed.It is found that permeability difference,reservoir pressure difference and gas bearing difference are the main factors affecting the interlayer interference.(2)The mechanism of interlayer interference in CBM coproduction is revealed.Based on the nuclear magnetic resonance experiment,the stress sensitivity of different reservoirs to pressure disturbance in the initial drainage stage is analyzed.The results show that stress sensitivity of the reservoir is low in the study area,but the stress causes permanent damage to the pore structure.In addition,the complex distribution of residual water in the pores has a negative effect on the expansion of the reservoir pressure drop funnel.Based on the physical simulation experiment of CBM coproduction in gas production stage,the controlling effect of reservoir heterogeneity difference on interlayer interference is revealed,and the model of productivity contribution rate considering effective stress effect and interlayer interference rate is established.The results demonstrate that the smaller the difference reservoir parameters,the more balanced the productivity contribution of each layer is.In the process of coproduction,permeability extreme difference and reservoir pressure difference aggravate the interference degree in the lower layer,while the difference of water saturation decreases the interference degree in the lower layer.In addition,the increase of effective stress and the decrease of permeability both increase the interference degree in the lower layer.(3)A quantitative identification model of interlayer interference degree is established and suggestions for reducing interlayer interference in the process of coproduction are put forward.Based on the plane radial flow equation and the material balance equation of CBM drainage,the mechanism of multi-seam reservoir heterogeneity on interference is deepened.The concept of interlayer interference coefficient is proposed,and the models of interlayer interference degree in different drainage stages are constructed.The interlayer interference between layers in different drainage stages of coproduction wells in the study area is quantitatively identified.Some suggestions are put forward to reduce interlayer interference in the process of coproduction.There are 82 figures,28 tables and 206 references in this thesis.