生油煤形成的环境制约

Environmental constraints on oil-generating coals

通过对不同沉积环境下形成煤系源岩生烃潜力的对比研究,揭示出成煤古环境对煤成烃生成具有控制作用,并根据煤系源岩中赋存大分子有机质裂解产物分子的组成特征,提出了识别有利成烃煤相的分子有机地球化学方法———氢指数-苯酚/辛烷图解判识法。结果表明,沼泽环境覆水越深,煤中有机质富氢程度越高,生油气性能越好,裂解产物表现为正构烷烃和正构烯烃相对含量增加,以低苯酚/辛烷值和高氢指数为特征;反之,沼泽环境覆水越浅,煤中有机质氢含量越低,裂解产物以高含量酚类化合物和芳香烃为特征,生油气性能差。由此表明,覆水型沼泽应是煤成烃,特别是煤成油生成的有利相带。

In potentially coal bearing petroliferous basins there is a need in petroleum exploration to predict ahead of drilling whether any coal bearing strata present are oil prone, and where the oil prone coal facies are. Theoretically, the evolution of depositional conditions within coal bearing sequence will result in the changes of biota community and affect the hydrocarbon generating potential of coal measures. In this study, coals from different depositional environments are organic geochemically compared, and beneficial coal facies for hydrocarbon generation have been identified using pyrolysis techniques in a sequence of stratigraphic framework. With the water table rising in swamps, organic matters from coal measures are more enriched in hydrogen. This can be attributed to an increased input of water column biota (e.g. algae) and the good preservation in the relatively anoxic conditions during peat deposition. The result suggests that coal seams deposited in interdistributary bay and lacustrine bog setting may possess the excellent potential to generate and release liquid hydrocarbons and may have general application to hydrocarbon exploration in areas thought to be sourced from coal bearing strata.