微生物降解天然气模拟试验

为研究天然气被微生物降解后组分及碳同位素组成的变化特征，在好氧条件下，进行了对降解原油及油井附近土壤中细菌的培养和富集，并将其接种到天然气的模拟降解试验中。结果发现：油田微生物能够对天然气烃组分进行降解，降解后iC₄/nC₄、C₀/nC₄、C₂/C₃、C₂/nC₄值升高，反映正丁烷比异丁烷、丙烷和乙烷更易被降解，丙烷比乙烷更易被降解；除CO₂的δ¹³C明显变轻以外，富集¹²C为7.4‰～11.9‰，重烃组分的δ¹³C变化均低于1‰，这可能与降解时间较短有关。组分及碳同位素组成特征均表明，相对于正丁烷而言，丙烷并未显示出优先被降解现象。少数样品接种的菌种中可能含有甲烷氧化菌，降解后甲烷δ¹³C变重，为1.8‰～1.9‰。

SIMULATING TEST OF MICROBIAL DEGRADATION OF NATURAL GAS

In order to study changes of gas component and carbon isotopic composition after microbial degradation of natural gas, microbes that degrade crude oil and live in near wellbore soils are cultured and enriched, then are used to perform simulating test of gas biodegradation. Oilfield microbes can degrade hydrocarbon components of natural gas. After biodegradation, iC4/nC4, C3/nC4, C2/C3 and C2/nC4 values increase, indicating that normal butane is easier to be biodegraded than isobutene, propane and ethane, and that propane is easier to be degraded than ethane. The variations of  13C values of heavy hydrocarbons are all lower than 1‰, except for that of CO2 which significantly get lighter, with enriched 12C in the range of 7.4‰ to 11.9‰, possibly due to the short time of biodegradation. Both gas component and carbon isotopic composition features show that biodegradation of propane has no priority over normal butane. The microbes inoculated in some samples may contain methane oxidizing bacteria, resulting in larger 13C value of methane ranging from 1.8‰ to 1.9‰.