渤海湾盆地济阳坳陷气源岩和原油生物模拟实验研究

SIMULATION EXPERIMENT OF BIOGENIC GAS FROM SOURCE ROCK AND BIODEGRADATION OF CRUDE OIL IN THE JIYANG DEPRESSION,THE BOHAI BAY BASIN

通过细菌检测实验,系统分析了渤海湾盆地济阳坳陷生物气源岩中细菌的赋存状况。实验表明,济阳坳陷浅层气源岩中产甲烷菌较为丰富,在2 522 m深处还有产甲烷菌存在,并且产甲烷菌赋存的源岩与源岩时代无相关关系,只要有适合生物气形成的环境条件,生化作用就可能发生。通过气源岩和原油在不同温度下的生物模拟实验,分析了济阳坳陷生物模拟气产率、组分及碳氢同位素特征,结果表明,无论是气源岩还是原油厌氧降解生成的生物气,都只生成甲烷和二氧化碳;45℃和65℃是生物气生成的高峰期,生物气产率分布范围为每吨TOC产气20~160 m3和每吨原油产气10~15 m3;生物模拟实验产物的碳同位素值随温度变化差异明显,变化范围为-80.2‰^-41.5‰;生成的二氧化碳的碳同位素值变化与甲烷碳同位素值变化规律相反;生物模拟气中氢同位素的值则比实际生物气的氢同位素值轻,模拟气中氢同位素值主要分布在-300‰^-350‰,而实际生物气的氢同位素值则分布于-240‰^-270‰。

Detection of the bacteria in the source rocks from different types of formation,lithology and depth in the Jiyang Depression was carried out in this paper.The result shows that the methane-forming bacteria exist in mudstone and sandstone in Es3,Es1 and Ed formations with depth being from 1 297 to 2 522 meters,indicating that the existence of methane-forming bacteria depends on the survival environment of the bacteria and is independent of rock's formation and lithology.The characteristics of the biogenic gases from source rocks and biodegradation of crude oil are similar in simulation experiment.The products of simulation experiment are mathane and carbon dioxide.Temperatures at the biogenic gas generating peak are 45 ℃ and 65 ℃.The yields of biogenic gases generated by a ton of TOC and a ton of crude oil are 20-160 m3 and 10-15 m3 respectively.Carbon isotope compositions of methane which range between-80.2‰ and-41.5‰ become lighter with simulation temperature going up,while carbon isotope compositions of carbon dioxide become heavier.Hydrogen isotope compositions of biogenic gas in simulation which mainly range between-300‰ and-350‰ are lighter than those in actual formation like the Luliang Basin in Yunnan Province which mainly range between-240‰ and-270‰.