超压环境有机质热演化和生烃作用机理

Kinetics of organic matter maturation and hydrocarbon generation in overpressure environment

通过对多个盆地大量样品的多参数对比分析,建立了超压抑制有机质热演化的多参数识别标志,揭示了不同成熟度指标对超压的差异响应。识别出超压抑制有机质热演化和生烃作用的4个层次:①超压抑制了有机质热演化的各个方面,包括不同干酪根组分的热降解(生烃作用)和烃类的热演化;②超压仅抑制了烃类的热演化和富氢干酪根组分的热降解,而对贫氢干酪根组分的热演化不产生重要影响,因此镜质体反射率未受到抑制;③超压抑制了烃类的热裂解,而对干酪根的热降解未产生明显影响;④超压对有机质热演化的各个方面均未产生可识别的影响。超压对有机质热演化的抑制作用层次取决于超压发育后有机质热演化反应的体积膨胀效应、产物浓度变化速率及超压的发育特征。早期强超压和长期保持封闭流体系统是产生第一层次超压抑制作用的必要条件。超压发育过晚、超压强度低、超压流体频繁释放等都可能导致超压对有机质热演化的各个方面均不产生可识别的影响。

The effects of overpressure on organic matter （OM） maturation and hydrocarbon generation were studied by multiple-parameter measurements. The differential responses of different maturity parameters to overpressure were found. Four hierarchies of overpressure retardation on the thermal evolution of organic matter and hydrocarbon generation were recognized. ①All aspects of OM maturation were retarded by overpressure. ②The thermal evolution of hydrocarbons and thermal degradation of hydrogen-rich kerogens were retarded, but the thermal evolution of hydrogen poor kerogen components was not affected by overpressure. As a result, vitrinite reflectance was not retarded. ③The thermal cracking of hydrocarbon was retarded, while overpressure had little effect on thermal degradation of kerogens. ④Overpressure had no detectable effect on All aspects of OM maturation. The hierarchy of overpressure retardation on the all aspects of OM maturation was the combined result of ＂early＂ overpressure, namely the overpressure began to develop when the source rock was still immature, and the protracted maintenances of closed fluid system. Any case that overpressure developed too late, or overpressure was too small to reach the threshold values, or overpressure fluid was frequently released, could give rise to the occurrence that overpressure had no detectable effect on All aspects of OM maturation.