茂名油页岩生烃演化特征及热解动力学——以琼东南盆地地质模型为例

Thermolytic dynamics and hydrocarbon generation characteristics of Maoming Oil Shale: Taking the geological model of Qiongdongnan Basin as an example

针对海上高地温场条件下天然气的生成和预测研究,选用琼东南盆地的地质模型,以低成熟茂名油页岩（Ⅱ型有机质）与该盆地的煤（Ⅲ型有机质）为样品,采用封闭体系和开放体系全岩热解实验,得出热解油气的产率特征.不同演化阶段各烃类组分的生烃动力学定量模型表明,煤生成不同组分的活化能分布范围比茂名油页岩的宽得多.其中,茂名油页岩热解生成甲烷、乙烷、丙烷和重烃（C4～6）对应的活化能分布范围分别为38～86 kcal/mol,44～92 kcal/mol,43～77 kcal/mol和46～70 kcal/mol;活化能主频分别为52 kcal/mol,54 kcal/mol,63 kcal/mol和48 kca1/mol,所占比例分别为20.44％、38.04％、42.50％和25.05％;指前因子分别为6.47×10^11s-1,2.70×10^12s-1,1.09×10^15 s-1和8.39×10^15s-1.利用生气动力学方法,结合琼东南盆地的热史数据,通过茂名油页岩和煤的生气预测对比揭示,在地质条件下的生气过程中,与茂名油页岩相比较,煤具有释放氢的慢速率与低生成率的特征以及较长的演化进程.结果认为：类似于琼东南盆地崖城组煤系烃源岩,处于海上高地温场条件下,在高演化阶段仍具有很好的生气潜力.该研究拓宽了我国海域煤型气的勘探领域,具有实践和理论意义.

In view of the natural gas generation and prediction problems under the condition of offshore high geothermal field, taking the geological model of Qiongdongnan Basin as an example, natural gas generation process was simulated by heating immature Maoming Oil Shale samples with kerogens of Ⅱ type and coal samples from the QiongdongnanBasin with kerogens of Ⅲ type. In order to determine the characteristics of the yields of oil and gas generation derived from pyrolysis, we adopted the hydrous pyrolysis experiments in the closed system and non-isothermal anhydrous pyrolysis experiments in the open system. The dynamics quantitative models of hydrocarbon generation of various hydrocarbon compositions in different evolution stages show that the range of activation energy distribution derived from different components of coal is much wider than that of Maoming Oil Shale. Among them, the ranges of activation energy distribution for methane, ethane, propane and heavy hydrocarbon （C4-6） generated by Maoming Oil Shale derived from pyrolysis are from 38 to 86 kcal/mol, 44 to 92 kcal/mol, 43 to 77 kcal/mol and 46 to 70 kcal/mol respectively. And the dominant frequency of activation energy are 52 kcal/mol, 54 kcal/mol, 63 kcal/mol and 48 kcal/mol respectively, their percent are 20.44%, 38.04%, 42.5% and 25.05% respectively, and the pre-exponential factors are 6.47×10^11 s-1, 2.70×10^12 s-1, 1.09×10^15 s-1 and 8.39×10^15 s-1 respectively. Using the kinetic methods of natural gas generation, combined with the thermal history data from Qiongdongnan Basin, we contrasted the prediction of natural gas generation between Maoming Oil Shale and coal. It indicates that coal of type Ⅲ releases hydrogen more slowly than Maoming Oil Shale of type Ⅱduring the thermal evolution, suggesting a lower hydrocarbon generative rate but a longer thermal evolutionary phase of hydrocarbon generation. The results reveal that： similar to the hydrocarbon source rocks of coal-measures in Yacheng Formation of Qiongdongnan Basin, Maoming Oil Shale in high thermal evolutionary phase still has fine potential of natural gas generation under the condition of offshore high geothermal field. This study is more theoretical and practical significance to coal-type gas exploration and development in the wider areas of Chinese Sea.