热解煤层气的氢同位素主控因素及其成因的示踪研究

Determinating of the geochemistry and genesis of coalbed gas are important to understand the formation and distribution law of coalbed gas reservoirs and to evaluate the coalbed gas resource. Hydrogen isotopic geochemistry of coalbed gas is an important part of coalbed gas geochemistry. The influencing factors, influence degree and genetic tracing indicators of coalbed gas hydrogen isotope are the scientific issues that need to be solved urgently. In this study, under high temperature and pressure, thermal simulation experiments will be performed on the peat and brown coal samples from different sedimentary environments, with different material properties and undergoing different diagenetic media condition. The components of the generated gases, hydrogen isotopic compositions of methane and ethane and vitrinite reflectance of the solid residues will be determined. The genetic relationship between the generated gas components and hydrogen isotopic compositions and sedimentary environment, material property, diagenetic media condition and maturity will be studied and further, the main controlling factors of coalbed gas hydrogen isotopic composition will be determined. The genetic model and mechanism of the coalbed gas hydrogen isotope will be established, and the hydrogen isotopic tracing indicators for genesis of thermal genetic coalbed gas formed under different sedimentary environment conditions will be determined. The formation mechanism of coalbed gas and its hydrogen isotope will be elucidated. This study will provide the scientific data and theoretic evidences for identifying the thermal genetic coalbed gas formed under different geologic conditions.

煤层气地球化学特征及其成因对于煤层气藏形成和分布规律的认识及煤层气资源评价至关重要。煤层气的氢同位素地球化学是煤层气地球化学的重要组成部分，并且煤层气氢同位素影响因素及其影响程度与成因示踪指标是目前迫切需要解决的科学问题。应用高温高压模拟实验方法，采用不同沉积环境和成岩介质条件下具有不同物质性质的泥炭及褐煤进行模拟实验，测定模拟获得的气体的地球化学组分与氢同位素组成和固体残查Ro值；研究这些气体的组分分布和氢同位素组成特征与沉积环境、成岩介质、物质性质、成熟度等因素之间的因果关系，确定煤层气的氢同位素主控因素；建立煤层气氢同位素地球化学的成因模式与机制，确立不同环境因素条件下形成的热成因煤层气成因的氢同位素示踪指标，阐明煤层气及其氢同位素的形成机制，为判识不同地质条件下形成的热成因煤层气提供科学数据和理论依据。

煤层气氢同位素影响因素及其影响程度与成因示踪指标是目前迫切需要解决的科学问题。本项目应用高温高压模拟实验方法，对不同地理位置和气候环境下形成的具有不同母质性质的褐煤和沼泽泥炭进行了加水及无水热模拟实验，测定了模拟获得的气体的地球化学组分与氢碳同位素组成和固体残查Ro值；研究了这些气体的组分分布和氢碳同位素组成特征与成煤物质性质、沉积环境、成岩水介质、成熟度等因素之间的因果关系。首次对比研究了草本沼泽和森林沼泽泥炭热解烃类气体的氢碳同位素组成特征与演化规律，发现热解的烃类气体氢碳同位素组成是草本沼泽泥炭轻于森林沼泽泥炭；确定了从泥炭连续演化至不同成煤阶段，不同性质成煤物质热解煤层气氢碳同位素组成的差异指标。对高纬度寒冷干旱和低纬度热带湿润环境的草本泥炭的热解烃类天气同位素研究发现，高纬度寒冷干旱环境的草本泥炭热解甲烷、乙烷和丙烷具有轻的氢同位素组成和重的碳同位素组成；首次建立了高纬度寒冷干旱和低纬度热带湿润草本沼泽环境中形成的成煤有机质热解烃类气体氢碳同位素组成与 Ro 之间的关系式，以及烃类气体的氢与碳同位素之间的关系式；提出了从泥炭连续演化至不同成煤阶段，不同成煤环境的草本泥炭成煤物质形成的煤层气氢碳同位素组成的差异指标。首次通过加入盐湖咸水和沼泽淡水成岩水介质，对草本成煤物质进行了热解模拟实验，研究了热解产物烃类气体的氢碳同位素组成及其差异性与演化规律，发现成岩水介质对热成因煤层气氢同位素组成具有显著的影响，对碳同位素组成影响较小；建立了盐湖咸水和沼泽淡水参与的热解烃类气体δD值与Ro的数学模型。研究揭示了在水介质参与下，煤化时间对成煤物质热解烃类气体氢同位素组成具有明显的影响。阐明了煤层气及其氢、碳同位素的形成机制。研究成果为判识不同地质条件下形成的热成因煤层气提供了科学数据和理论依据。