Study On The Removability Of Multi-layer Stacked Coal Reservoir In Laochang Block Of Eastern Yunnan

The coal seam in the Laochang area in the east of Yunnan is thin and numerous in the longitudinal direction.At the same time,the in-situ stress is high,the coal structure is complicated,and the development of coal bed gas is difficult.This article takes the coalbed methane wells in the Laochang mining area as the research object,statistics a large number of coal field exploration data and coalbed gas logging test data,and analyzes the coal reserves in the Laochang mining area from the aspects of stratum combination,coal structure,in-situ stress,and rock mechanics.The reformability of the formation and the grey clustering method were used to establish a preliminary evaluation system for the reformability of the coal reservoirs in the study area.The gas-bearing system sections suitable for reconstruction were selected to provide a basis for the fracturing of coalbed gas wells in the later stage.Comprehensive analysis of the characteristics of the four aspects of stratum combination,coal structure,rock mechanical parameters and in-situ stress parameters,and in the gas bearing physical property system,the evaluation unit is divided according to the criteria that the total thickness of evaluation unit is less than 30 m,the thickness of single coal seam is more than 2m,and the thickness of multiple coal seams and single coal seam is more than 1.5m.The coal thickness in the study area is concentrated at about 2m as a whole,with medium-thick coal seams as the mainstay,and the coal seam spacing has a relatively large change.The lithology of the top and bottom floors is mainly argillaceous siltstone,silty mudstone,and mudstone.Among them,argillaceous siltstone has a high elastic Young's modulus,and mudstone has a low elastic Young's modulus.The coal structure divided based on the logging curve increases with the burial depth in the vertical direction,and the proportion of primary + fragmented coal increases.In addition,the study area as a whole is in a medium-strong stress zone.The stress state,stress ratio,and lateral pressure coefficient of coal reservoirs change at 400 m and 800 m,showing different changes.The permeability of coal reservoir decreases with the increase of the minimum horizontal principal stress of the effective level and changes in sections with the increase of the buried depth.Based on a comprehensive analysis of the influencing factors of reservoir reconstruction,combined with the actual situation in the study area,specific indicators for each category of transformability evaluation are determined,that is,coal thickness,coal thickness + sandstone / unit thickness,coal body structure,and equivalent elasticity of coal seams.Young's modulus,Young's modulus ratio of coal to roof and floor,equivalent Poisson's ratio of coal seam,Poisson's ratio of coal to roof,floor minimum principal stress,stress ratio,and horizontal stress difference coefficient,among which coal thickness,coal thickness + sandstone / Unit thickness,elastic Young's modulus-related parameters,and horizontal stress difference coefficients are positive factors for the evaluation of the modifiability,while coal structure,Poisson's ratio-related parameters,the minimum horizontal principal stress,and the stress ratio are the negative factors for the evaluation of the modifiability.At the same time,ward clustering was used to quantify 10 evaluation parameters into four levels.The grey clustering + analytic hierarchy process method was used to evaluate the reservoir transformability in the Laochang area of eastern Yunnan,and it was proved that the transformability is good and lacks high quality transformable reservoirs.Gas-bearing system ? and gas-bearing system ? are generally more reproducible than gas-bearing system ?.