Generation of nitrogen and methane from sedimentary organic matter: Implications on the dynamics of natural gas accumulations
Generation of nitrogen and methane from sedimentary organic matter: Implications on the dynamics of natural gas accumulations
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DOI：
10.1016/0009-2541(95)00124-7
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发表时间：
1995-12-20
期刊：
影响因子：
3.9
通讯作者：
Idiz, EF
中科院分区：
文献类型：
--
作者：
Krooss, BM;Littke, R;Idiz, EF
德国北部盆地Rotliegend和Buntsandstein储层天然气氮(N-2)含量区域性接近100%。回顾了为解释该地区和世界其他地区的氮异常而提出的各种假设（原始起源、火山或岩浆起源、放射成因、大气起源、有机起源、沉积岩中的无机氮）。本研究的目的是调查沉积有机质，特别是煤，作为地下分子氮的潜在来源。储层规模和天然气生成潜力的比较表明，石炭纪煤系被认为是德国北部盆地天然气的来源，可以很容易地解释当今储层中发现的氮含量。进行了实验室热解实验，研究了不同类型和等级的煤产生甲烷和分子氮的动力学。在实验条件下，氮气在比甲烷更高的温度下形成，支持自然系统中甲烷和氮气“部分生成”的概念。根据实验室实验得出的动力学参数，计算了煤中甲烷和氮气的生成速率，以计算地质加热速率。在这些条件下，在超过300摄氏度的温度下，产生含有超过50%氮气的气体。因此，仅在甲烷产生实际上停止之后的气体产生的最后阶段才形成富氮气体。结论是，富氮气体聚集中遇到的气体量仅占该区域总气体生成潜力的一小部分（可能<1%），而大部分生成的气体已逃逸到大气中。目前储层气体的成分仅反映了最近生成的气体（在地质时间尺度上）的成分。
Nitrogen (N-2) contents of natural gases in Rotliegend and Buntsandstein reservoirs of the North German basin regionally approach 100%. A review is given of the various hypotheses (primordial origin, volcanic or magmatic origin, radiogenic origin, atmospheric origin, organic origin, inorganic nitrogen in sedimentary rocks) presented to account for nitrogen anomalies in this area and other parts of the world. The objective of the present study was to investigate sedimentary organic matter, in particular coals, as a potential source of molecular nitrogen in the subsurface. Comparison of reservoir sizes and gas generation potentials indicates that Carboniferous coal measures, which are considered as the source of the natural gas in the North German basin, can readily account for the nitrogen quantities found in present-day reservoirs. Laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank. Under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a 'fractional generation' of methane and nitrogen in natural systems. Based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates. Gas containing more than 50% nitrogen is generated under these conditions at temperatures in excess of 300 degrees C. Nitrogen-rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased. It is concluded that the amounts of gas encountered in nitrogen-rich gas accumulations represent only a small fraction (possibly < 1%) of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere. The present-day composition of the reservoir gases reflects the composition of only the most recently generated gas (on a geologic time scale).