The Characteristics Of Coal Reservoir And Its Coalbed Methane Distribution Controlled By Tectonism In Guojiahe Coal Mine,yonglong Mining Area

The characteristics of coal reservoir and heterogeneity distribution of coalbed methane controlled by tectonic setting are scientific challenge to high efficiency on coalbed methane production.The heterogeneity of pores and fracture characteristics effects the adsorption ability and permeability of coalbed methane,which are restrictive factors of the CBM production.Besides,the distribution of the geological tectonics controlled the process of generation,accumulation and preservation which determines the CBM exploration target.In this dissertation,we took Guojiahe coal mine as the study area to explore the characteristics of the coal reservoir and the CBM distribution controlled by tectonics,predict the gas content and propose a method on the quantity prediction of coalbed methane resources.The study is of importance and has application value of the CBM exploration and production.In terms of structural characteristics research on reservoir,we analyzed gas content,absorbability permeability and their influence factors.It is found that No.3 coal seam is a gas bearing reservoir with low absorbability,low gas content and low permeability.We discussed the differences between intact coals and cataclastic coals on pores shape,BET specific surface area,BJH pore volume and their connectivity.It is found that cataclastic coals have a better adsorption and connectivity performance with a large amount of fracture pores.Besides,we also explored the distribution characteristics of different size of fractures in the coal reservoir and discussed structural properties of the microfractures in coal samples.It is found that the microfractures are well developed in the cataclastic coals with large density,length and width.Based on fractal theory,the fractal dimensions of coal samples were calculated and the non-linear relationships between fractal dimensions of pores and microfractures and their permeability were concluded.On macroscopic aspect of gas distribution controlled by tectonism,we simulated the history of subsidence,analyzed structural evolution characteristics and hydrocarbon generation history.It is found that the Jurassic strata was settled stably for a long time and had a short-time hydrocarbon generation period in Early Cretaceous.Thus,the content of coalbed methane is quite low in the study area.On the basis of geological tectonic distribution interpreted by three dimensional seismic technologies,it can be known that correctional gas content distribution varies with the location of structure.Thus,the gas controlling structures could be sorted according to the gas content and then could be classified into 3 types and 6 positions including gentle dip anticline,syncline and secondary anticline and normal fault,specifically including low buried gentle fold limb,syncline axis,rising end of syncline,intersection of syncline and secondary syncline,anticline axis and secondary anticline limb with normal faults.Besides,the relationship between structural complexity and gas content was presented.Specifically,the gas content in simple structural region is larger than 3.5m3/t,it varies from 2 to 4m3/t in simpler region,it varies from 1.5 to 2.5m3/t in less complex region and it is lower than 1.5m3/t in complex region.Furtermore,we built a coupled thermal-hydraulic-mechanical model to study the differences on total gas content,temperature,pressure and permeability of coal seams during mining based on tectonic detailed interpretation.We also revealed the change rule of total gas content of coal seams distributed at different parts of tectonic structures and then discussed the distribution regularity of total gas content and reservoir permeability near faults.The results show that the reservoir at broad gentle syncline axis exhibits high temperature,pressure and gas content but low permeability.While the reservoir at broad gentle anticline axis and normal fault plane exhibits low temperature,pressure and gas content but high permeability.Gas content and reservoir permeability are affected by normal faults and the range of influence is 37m and 54m of the fault plane respectively.The gas content at the fault plane with above 86%drop but the permeability reaches the peak with 2.6%growth.Considering the coal thickness,upper strata thickness and lithology of surrounding rocks,a classic geological cross-section was selected to verify the rule of gas content controlled by tectonism.In terms of gas richness prediction of coal seams and precise estimation of CBM resource,based on simulation equation related to gas content distribution controlled by tectonism,gas content coefficient was proposed.Then a gas richness prediction model of coal seams based on structural complexity was built which provides a new method for gas richness detailed prediction.Besides,CBM resource precise estimation model was proposed by three-dimensional integration algorithm.The accuracy of the model result was verified by the actual quantity of CBM resources in 1302 working face.We also calculated the quantity of coalbed methane resource in Guojiahe coal mine.It indicates that the precise estimation model provides a new method for CBM resources estimation.