珠江口盆地惠州凹陷古近系文昌组优质湖相烃源岩生烃动力学

Kinetics of high-quality lacustrine source rocks of Paleogene Wenchang Formation,Huizhou Sag,Pearl River Mouth Basin

基于两种升温速率下的玻璃管封闭体系烃源岩生烃模拟实验,最大程度排除烃类裂解的影响,揭示了珠江口盆地惠西南地区古近系文昌组半深湖相优质烃源岩的生油与生气的绝对产率及其与成熟度的理论共变模式。通过生烃模拟实验提供的精确产率数据,首次建立了该区文昌组优质烃源岩生成重烃(C_(14+))及降解气(C_(1-5))的动力学模型参数。利用地质推演的手段重建了半深湖相烃源岩生成重烃-烃气转化率与地层温度的理论协变关系,结合生烃洼陷的埋藏史-热演化史,认为惠州26洼文昌组半深湖相优质烃源岩的生烃演化进程具有“早油晚气”的特点,早期石油快速生成,对应的地质年代跨度介于40~15 Ma,地温范围为95~160℃,而晚期主力烃源岩生成大量天然气,对应的地温范围为119~205℃,烃源岩现处于生气阶段的末期。

The hydrocarbon yields of high-quality semi-deep lacustrine source rocks in the Wenchang Formation from the southwestern Huizhou Sag,Pearl River Mouth Basin,is simulated by the glass-tube pyrolysis experiment under two heating rates in which the thermal crack of hydrocarbon can be avoided to the maximum degree to establish for the first time the kinetic models of heavy hydrocarbon(C_(14+))generation and gas(C_(1-5))thermal degration.The theoretical relationship between the transformation ratio and the geological temperature of semi-deep lacusrine source rocks is reconstructed based on the geological extrapolation.It is suggested that the hydrocarbon generation of source rocks in the Huizhou-26 low exhibits the characteristics of“early oil and late gas”.The rapid generation of heavy hydrocarbon(oil)in the early stage corresponds to a geo-temperature from 95℃to 160℃and an age from 40 Ma to 15 Ma.While the large-scale generation of light hydrocarbons(gas)during the late stage corresponds to a temperature range of 119℃to205℃.The source rocks currently are at the end of its major gas generation stage.