Experimental Study On The Impact Of Anaerobic Biodegradation On Coal Pore Characteristics

The adsorption and seepage capacity of coal reservoirs is determined by the characteristics of pore development in coal.In order to study the effect of anaerobic biodegradation on the pore characteristics of full-bore sections in different rank coal,anthracite in Sihe mine,bituminous coal in Tunlan mine and lignite in Baorixile open pit mine were used as substrates in this paper.The microflora with fungi and methanogens enriched from the produced water of CBM well in Sihe mine was employed to perform the anaerobic biodegradation.High pressure mercury injection,low temperature liquid nitrogen adsorption,low temperature carbon dioxide adsorption,Sierpinski fractal model,and FHH fractal model were used to characterize the changes in pore parameters and fractal characteristics of coal after degradation.Sodium 2-bromoethanesulfonate(BES)was added to inhibit methanogenic activities and promote the accumulation of intermediates.The organics were extracted through solvent extraction,and determined by gas chromatography-mass spectrometry(GC / MS)to analyze the retention effect of anaerobic metabolites in coal.Field emission scanning electron microscopy was employed to analyze the adhesion effect of microorganisms on coal surface.Then the mechanism of microbial anaerobic degradation on coal pore development was explored.The main findings are as follows:(1)As the coal rank decreases,the biomethane production gradually increases.The lignite biomethane production is up to 166.55 ?mol,while anthracite is 51.16 ?mol.After adding the methanogenesis inhibitor BES,biomethane generation was significantly inhibited under different coal ranks.(2)The pore volume and specific surface area of residual anthracite at full pore size are significantly reduced.The pore volume of large pores and mesopores in residual bituminous coal increases slightly,while the pore volume of micropores and ultramicropores decreases significantly.The macropores and pore volume of mesopores in residual lignite increased obviously,but the pore volume of ultra-micropores,micropores and transition pores decreased slightly.The roughness of micropores surface in anthracite and bituminous coal increased,while the complexity of transition pores decreased.No significant changes have occurred in other pore fractal features.(3)Oxygen-containing aromatic derivatives and heterocyclic organics produced by microbial anaerobic degradation have a significant retention effect in coal,and it is found that the retention effect gradually weakens as the coal rank decreases.(4)A large number of rod-shaped,spherical and filamentous microorganisms are attached to the surface of residual coals with different ranks,and some microorganisms also adhere around and inside the seepage holes,of which the strongest adhesion effect is observed in anthracite.(5)The changes in pore development in anthracite,bituminous coal and lignite after anaerobic degradation of microorganisms are mainly caused by the combined effects of microbial dissolution,retention effect of anaerobic metabolites and adhesion effects of microorganisms.