Assessment of the petroleum generation potential of Lower Carboniferous coals, North Sea: evidence for inherently gas-pronesource rocks
Assessment of the petroleum generation potential of Lower Carboniferous coals, North Sea: evidence for inherently gas-pronesource rocks
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DOI：
10.1144/1354-079306-723
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发表时间：
2007-08
影响因子：
1.7
通讯作者：
H. Petersen;H. Nytoft
中科院分区：
文献类型：
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作者：
H. Petersen;H. Nytoft
对北海中央地堑丹麦Gert-2井和挪威2/11-9井下石炭统滨海平原煤的生油潜力进行了评价，以确定煤的源岩质量，并与深部储层相联系。煤的H/C比值在0.75 ~ 0.79之间，氢指数（HI）值在171 ~ 219之间，与热成熟时的HImax值非常接近。Gert-2煤热成熟度接近有效油窗（排油）起点，镜质组反射率为0.90 ~ 0.95%。脂肪链>C18在煤中所占的比例可以忽略不计或很低，C19-35脂肪链仅占煤结构中C12-35脂肪链总量的6%。脂肪族的特点是短链脂肪族和分离的CH2。生成的液态石油被困在煤中，饱和烃馏分以短链脂肪烃为主。经溶剂萃取后，Gert-2煤的实测HI值平均可降低30%，表明圈闭石油对实测生气潜力有贡献。因此，下石炭统煤具有固有的气倾向，这是它们与石炭系煤的一个共同特征，与成熟度无关。饱和烃的低效排烃可以通过烃源岩内油气裂解提高产气性。在北海地区的深部勘探背景下，下石炭统煤/煤段只能构成气源岩。
The petroleum generation potential of Lower Carboniferous coastal plain coals in the Danish Gert-2 and Norwegian 2/11-9 wells in the Central Graben, North Sea, has been assessed in order to determine the source-rock quality of the coals in connection with deeper plays. The coals are vitrinite-rich, have H/C ratios from 0.75–0.79, and hydrogen index (HI) values from 171–219, which are very close to the HImax values attained during thermal maturation. The thermal maturity of the Gert-2 coals is close to the start of the effective oil window (oil expulsion), c. 0.90–0.95% vitrinite reflectance. The proportion of aliphatic chains >C18 in the coals is negligible or very low: the C19–35 aliphatic chains constitute only c. 6% of the total amount of C12–35 aliphatic chains in the coal structure. Aliphatic moieties are characterized by shorter-chain aliphatics and isolated CH2. The generated liquid petroleum is trapped in the coals and the saturated hydrocarbon fraction is dominated by shorter-chain aliphatics. Upon solvent extraction, the measured HI values of the Gert-2 coals can, on average, be reduced by 30%, indicating that the trapped petroleum contributes to the measured generation potential. The Lower Carboniferous coals are thus inherently gas-prone, a feature they have in common with Carboniferous coals in general and which is not maturity related. Inefficient expulsion of the saturated hydrocarbons may enhance the gas-proneness by intra-source rock oil-to-gas cracking. In a deep exploration context in the North Sea area, Lower Carboniferous coal/coaly sections can therefore only constitute a gas source rock.