当前煤与瓦斯突出物理模拟试验多采用二氧化碳代替甲烷，导致试验结果偏差较大。为了保证模拟试验相似性并规避甲烷气体带来的安全风险，提出了甲烷相似气体的概念。基于瓦斯在突出过程中的作用机制和相似准则，结合煤与瓦斯突出防治规定，建立了以瓦斯含量、瓦斯放散初速度、初始瓦斯膨胀能和含瓦斯煤力学性质为参数的相似指标。初步采用二氧化碳体积分数为20%、40%、60%、80%的二氧化碳和氮气二元混合气体作为甲烷相似气体的筛选气体。按照相关规范，分别测定了甲烷和筛选气体的相似指标参数值，确定了与瓦斯含量、瓦斯放散初速度、初始瓦斯膨胀能和含瓦斯煤力学性质接近的混合气体组分分别是二氧化碳体积分数为60%、35%、45%和54%。相关性分析结果表明，上述4种配比气体与甲烷性质相关性高，可以作为相似气体的待定气体。采用待定气体和甲烷进行了模拟试验，结果表明，二氧化碳体积分数为45%的混合气体的突出现象和突出临界值与甲烷接近，与甲烷相似性高。

At present, CH4 is replaced by CO2 in physical simulation test of coal and gas outburst, which causes a large deviation of the results. In order to ensure the similarity of simulation test while avoiding the risk of CH4, a concept of similar gas which is close to CH4 is put forward in the physical simulation experiment. Based on the mechanism of gas in outburst and similarity criterion, several similarity indices including gas content, initial velocity of gas emission, initial gas expansion energy, mechanical properties of coal containing gas are presented by combination with the coal and gas outburst prevention provisions. The mixture of CO2 and N2 is used as the original similar gas, CO2 volume fraction of which are 20%, 40%, 60% and 80%. According to the relevant specifications, the similarity indices of CH4 and the similar gases are measured respectively. The mixed gases, whose volume fraction of CO2 are 60%, 35%, 45% and 54% respectively, are similar to CH4 in the gas content, the initial velocity of gas emission, the initial gas expansion energy, the mechanical properties of coal containing gas. Correlation analysis results show that the four mixed gases are highly relational to CH4, and can be used as undetermined gases of similar gas. Simulation tests on the undetermined gases and CH4 are carried out. It is found that the phenomenon and the critical value of mixed gas with a CO2 volume fraction of 45% are the closest to those of CH4.