Effects Of High Temperature Heat Treatment And Oxidation On Permeability Of Coal Rock

Coalbed methane(CBM)is a kind of high-quality and clean energy,and its economic and effective development has important practical significance for obtaining clean energy,improving the operation safety of coal mine and protecting the environment.CBM exists in the micropores of the coal matrix in adsorbed state,and the production of CBM undergoes three processes of desorption-diffusion-seepage.Undoubtedly,improving the permeability of coal reservoirs is crucial for the effective development of CBM.At present,most of coal reservoirs in China have the characteristics of low porosity,low permeability,low pressure and low saturation,conventional stimulation technologies and depressurization technologies are difficult to work.Therefore,based on the viewpoint of "net removal of materials-reducing materials to increase production",the recovery factor of CBM can be enhanced by applying High-temperature heat treatment and Strong oxidizer treatment to stimulate coal reservoirs.In this paper,tha coal samples are mainly taked from coal seams of the Jurassic Xishanyao Fm in the heishan Coal Mine,Tuokexun,Xinjiang.This paper studies the effects of Hightemperature heat treatment and Strong oxidizer treatment on the permeability of coal,and clarifies the mechanisms of High-temperature heat treatment to improve the seepage capacity of coal,the mechanisms of Oxidation to improve the seepage capacity of coal,the synergistic mechanisms of High-temperature heat treatment and Oxidation to improve the seepage capacity of coal.And the application prospects of High-temperature heat treatment and Strong oxidizer treatment are prospected.The mechanisms of High-temperature heat treatment to improve the seepage capacity of coal are clarified.The test results of the permeability and mechanical properties of coal after heat treatment show that the permeability of coal increases with the increase of heat temperature,which is lower than the threshold temperature Tc(Tc,LR=100??200?,TC,HR=400??600?),the permeability of coal increases slowly(The increasing rate of permeability vLR=0.008mD/?,vHR=0.022mD/?),which is higher than Tc,the permeability of coal increases greatly(vLR=0.031mD/?,vHR=0.327mD/?).The stress sensitivity of coal enhances with the increase of heat temperature.Industrial analysis,scanning electron microscopy and low temperature nitrogen adsorption experiments indicate that after heat treatment,only the water dispersion of coal is lost below Tc,and higher than Tc,the organic matter is pyrolyzed and escaped.The specific surface area and total pore volume of coal are increased.The primary cracks are expanded and new cracks are formed,forming a developed fracture network.The mechanisms of Oxidation to improve the seepage capacity of coal are revealed.The test results of the permeability and dissolution rate of coal and performance parameters of immersion solution show that the permeability of coal is significantly improved after the oxidation(KH2O2/K0=1.048?7.407,KClO2/K0=1.222?5.620),and the permeability enhancement effect of alkaline oxidizer is better than that of acidic oxidizer.The denser the coal,the higher the concentration of oxidizer and the longer the oxidation time,the more obvious the effect of the oxidation.X-ray diffraction,canning electron microscopy,low temperature nitrogen adsorption,infrared spectrum and wetting angle measurement experiments indicate that organic matter and pyrite are oxidized and consumed easily,and the generated H+ and small molecule aliphatic acids will dissolve inorganic mineral components further.A large number of microfractures and dissolved pores are formed in coal after the oxidation.The amount of associative hydroxyl and carboxyl functional groups on the surface of coal increase,and the water wettability on the surface reduces.The synergistic mechanisms of High-temperature heat treatment and Oxidation to improve the seepage capacity of coal are discussed.The coal which has been heat treatment is oxidated,the imbibition of coal is enhanced making that a large amount of oxidizer enter the matrix quickly,and the fracture toughness of coal is reduced,which are beneficial to improve the effect of the Oxidation.The coal which has been oxidizer treatment is heated,the reorganization of coal structure makes that the threshold temperature decrease,and the mechanical strength of coal is decreased,which are beneficial to improve the effect of High-temperature heat treatment.The application prospects of High-temperature heat treatment and Strong oxidizer treatment are prospected.High-temperature heat treatment is suitable for high-rank coal reservoirs.Strong oxidizer treatment is suitable for low-rank coal reservoirs.Strong oxidizer treatment-High temperature heat treatment can be applied to coal reservoirs with the depth of less than 1500?2000m and low-rank coal reservoirs.High temperature heat treatment-Strong oxidizer treatment can be applied to coal reservoirs with the depth of more than 1500?2000m,anhydrous coal reservoirs and high-rank coal reservoirs.