Study On Division And Optimum Selection Of ’Three Gases’ Co-mining Strata In Coal Measures

The coal bearing strata in Jinsha area of Northern Guizhou have rich potential of coal measure gas resources and various types of reservoirs,with the characteristics of thin single layer,many layers and large total thickness.Vertically,the gas content and reservoir conditions are highly heterogeneous and difficult to develop.The problem of co-mining compatibility compatibility is prominent.In this study,the upper Permian Longtan Formation coal measures strata in Jinsha area as the research object,using the method of combining field reconnaissance and experimental test,through the analysis of the key geochemical characteristics,gas bearing characteristics,lithology combination characteristics,porosity and permeability characteristics,formation pressure characteristics,formation temperature characteristics,in-situ stress characteristics,etc.,which affect the effect of coal measures gas co-mining,the evaluation index system of coal measures gas co-mining section suitable for the geological conditions of the study area is constructed,and the optimization method of coal measures gas co-mining section is put forward,and the coal measures gas co-mining sections of Longtan Formation in well JS-C in Jinsha area are divided and optimized.The following results have been achieved:(1)Through organic abundance test,field analysis,isothermal adsorption and other experiments,the organic matter type,maturity,abundance,gas content and other parameters of Longtan Formation coal measures reservoir in the study area are analyzed.It is considered that the Longtan Formation coal measures gas resources in the study area are large,but there is a strong vertical difference in gas content.According to gas content,Longtan Formation is divided into three sections with resource potential.(2)The resource potential interval 1 is characterized by thin single layer,frequent interbedded layer,large gas content,mainly coalbed methane,brittleness and strong rigidity,relatively good porosity and permeability,formation pressure and temperature are slightly lower than normal pressure and temperature,and the maximum horizontal stress is the main ground stress.The resource potential interval 2contains the least gas and is dominated by tight sandstone gas and coalbed methane,with poor brittleness,poor mechanical properties and strong longitudinal heterogeneity.Resource potential interval 3 has thick single layer and stable deposition.It is dominated by coalbed methane and shale gas,with the largest gas content.Its brittleness and rigidity are slightly inferior to that of member 1,and the ground stress is mainly vertical stress.(3)On the basis of previous research experience,the evaluation index system of coal measures gas combined mining section in the study area is constructed.Three first-level indicators including regional geological background,reservoir characteristics and deep formation characteristics are mainly determined,and ten second-level evaluation indicators including formation deposition,tectonic activity,hydrogeological conditions,resource potential,petrology characteristics,porosity and permeability characteristics,mechanical properties,formation pressure,formation temperature,ground stress and their lower limits are determined.The optimization method of coal measures gas co-mining interval based on GIS,analytic hierarchy process and fuzzy evaluation method is proposed.Among them,GIS is used to screen the development potential layers of coal-bearing gas reservoirs.Weights of each index in evaluation system of co-mining interval in coal measures determined by analytic hierarchy process.The score of each potential layer is determined by fuzzy evaluation method.Through analysis and calculation,the maximum weight of resource potential condition is 0.35.Sedimentary strata,0.18;the petrology characteristics and porosity and permeability characteristics are 0.13 again.(4)According to the evaluation model of co-mining intervals in coal measure gas co-mining layers,four potential intervals are selected from Longtan Formation of JS-C well.The fourth potential interval is the best,the horizontal well directional perforation is used for production.The development potential interval 1 is slightly inferior,which should be mined by continuous perforating in vertical Wells.Development potential interval 2 and 3 are not considered for the time being.