基于氮吸附、压汞联合试验的CO2致裂对煤岩孔隙的影响

煤岩中的孔隙结构特征对瓦斯运移和富集有着至关重要的影响。为了研究CO₂致裂对煤岩孔隙的影响,利用低温氮吸附试验与压汞试验相结合的方法对致裂前后的煤岩孔隙变化进行定量表征,并使用扫描电镜、现场致裂后煤岩瓦斯抽采分别从定性和宏观上反映CO₂致裂对煤岩孔径分布和孔隙结构特征的影响。结果表明,CO₂致裂会迫使煤岩中微孔、小孔孔隙结构改变,从墨水瓶形孔转变为开放型孔隙,各孔径段孔容有所增长扩张,致裂主要迫使孔径在10 000~100 000 nm的孔隙有较为明显的发育扩张。煤岩中存在渗流孔隙和扩散孔隙,致裂后渗流孔体积和百分比呈现先增长后逐步降低的现象,扩散孔体积变化趋势与渗流孔一致,但其百分比先降低后逐步回升。通过扫描电镜、现场测定及计算等辅助手段从宏观方面反映出CO₂致裂对孔隙有明显作用,对消除煤与瓦斯突出有积极效果。

Influence of CO2 cracking on the coal and rock pore based on the nitrogen adsorption and mercury press com-bined experiment

The present paper is to engage itself in a study of the effect of carbon dioxide cracking on the coal rock pores with the method of low-temperature nitrogen adsorption along with the mercury intrusion. The said experiment can help to specify and determine quantitatively the pore changes in the coal rock pre-&-pro cracking. The research need comes from the vital impact of the pore structure in the coal rock on the gas migration and enrichment. Besides,it is also necessary to analyze qualitatively and macroscopically the effects of the carbon dioxide crack on the pore size distribution and the pore structure of coal and rock by the electronic microscopic scanning(EMS) and measuring the natural flow and gas permeability coefficient of the coal gas as the result of cracking. The results of the above experiment can also exhibit that the carbon dioxide cracking helps to force the pore structure of the microspore in the coal rocks to change from the ink-shaped pores to the open ones so that the capacity of each pore size segment can expand and push the cracking of the pores with the size of 10 000-100 000 nm to exhibit their visible development and expansion. And,in accordance with the existence of the seepage pores and diffusion pores in the coal rocks,the seepage pores as the result of the crack can gradually exhibit the lower growth of increase in the content and the percentage change.The change of the diffusion pores should be consistent with the trend of the seepage pores,but their percentage change may first gradually contract and then expand. Therefore,with the help of the electronic scanning microscopy,the measurement of the gas natural flow change and the calculation of the gas permeability coefficient and the other auxiliary means can help to conclude that the carbon dioxide cracking has a significant impact on the pores and the elimination effect on the coal and gas outburst.