烃源岩生烃抑制模拟实验及机理

为探索高压条件下烃源岩生烃抑制机理,利用济阳坳陷页岩样品,以热解实验求取了开放体系生烃动力学参数,并进行了高压条件下和封闭条件下生烃模拟实验。对比高压生烃模拟实验转化率和利用动力学参数计算的开放体系转化率:在高压条件下各个样品的生烃转化均受到一定程度的抑制,但生烃抑制程度不同,有机质原始生烃能力越强(原始热解S_2越高),其抑制作用越明显;生烃转化率的抑制程度与烃源岩内滞留烃量正相关,滞留烃含量越高、生烃抑制越明显。封闭条件模拟实验表明:在同样的封闭条件下,生烃转化率与有机质原始生烃能力负相关,原始生烃能力越高、转化率越低;烃源岩生烃过程中存在着化学平衡,而生成烃类的大量滞留会导致有机质生烃的逆反应速率增加,减缓整体反应速度;烃源岩生烃抑制可能是生成的烃类流体排出不畅、生烃逆反应速率增加等原因所导致,而高压只是封闭性的客观反应,烃源岩非生烃成因导致的异常高压与生烃抑制可能不存在必然联系。

Simulation experiment and mechanism of hydrocarbon-generation retardation for source rocks

To explore the hydrocarbon-generation retardation mechanism for source rocks in high-pressure environments, the hydrocarbon-generation kinetic parameters in an open system were obtained by pyrolysis experiments using the shale samples of Jiyang depression. Meanwhile, the simulation experiments of hydrocarbon generation are carried out under high pressure conditions and confined conditions respectively. A contrast is made between the conversion rate of hydrocarbon generation under high-pressure conditions obtained by the simulation experiment and that in an open system calculated by kinetic parameters. The results show that under high pressure conditions, the hydrocarbon-generation conversion of each sample is retarded to some extent, but their retardation extents are different. The stronger the initial hydrocarbon-generation capacity of organic matter is(the higher the initial pyrolysis S₂ is), the more obvious the retardation effect will be. Moreover, the retardation extent of hydrocarbon-generation conversion is positively correlated to the residual hydrocarbon amount in source rocks. The higher the residual hydrocarbon content is, the more significant the hydrocarbon-generation retardation effect will be. The simulation experiments under confined conditions indicate that under the same confined conditions, the hydrocarbon-generation conversion rate is negatively correlated to the initial hydrocarbon-generation capacity of organic matter. The strong the initial hydrocarbon-generation capacity is, the lower the conversion rate will be. In addition, chemical equilibrium exists in the hydrocarbon generation process of source rocks, while massive retardation of the generated hydrocarbon will lead to an increase in the reverse reaction rate of hydrocarbon generation for organic matter and the reduction of overall reaction rate. The hydrocarbon-generation retardation of source rocks may be caused by unsmooth discharge of the generated hydrocarbon fluids, an increase in the reverse reaction rate of hydrocarbon generation and other reasons. However, high pressure is only an objective response for confined conditions, and there may be no necessary relation between the abnormal high pressure induced by non-hydrocarbon-generation genesis of source rocks and the hydrocarbon-generation retardation.