珠一坳陷近源及远源油气富集主控地质因素统计与油气运移物理模拟实验

Statistics on the main geological factors controlling hydrocarbon accumulation of near and distal sources in ZhuⅠdepression and the physical simulation experiment of hydrocarbons migration

以珠一坳陷烃源岩(文昌组)的上覆直接盖层(恩平组)岩性组合、T70界面油源断层断距及已发现油气在断-坳构造层间分配占比等三者之间的地质统计分析为基础,探讨了该地区近源与远源油气富集主控因素,建立了油气穿越烃源岩上覆直接盖层运移的地质模型,开展了不同砂地比与断层断距组合条件下的油气运移物理模拟实验。统计分析表明,文昌组烃源岩的上覆直接盖层恩平组的岩性组合与断裂发育特征控制了油气在断陷期构造层(近源)及拗陷期构造层(远源)的富集程度,当恩平组砂地比低于35%时,油气主要在T70界面之下地层中聚集;当恩平组砂地比高于35%、油源断层断距在100 m以上时,有利于油气在T70界面之上地层中聚集。物理模拟实验表明,地层砂地比越高、断距越大,油气越容易穿越盖层向上运移;盖层内的油气运聚主要受控于断层断距与地层砂地比,砂地比为30%~50%时有利于油气在盖层内运聚。建议结合烃源岩生烃史模拟分析开展洼陷内烃源岩上覆直接盖层的岩性组合与断裂发育程度的时空匹配关系评价,更好地为该地区准确预测主力油气成藏组合及有利勘探方向提供参考依据。

Through statistically analyzing the lithologic association of the overlying direct caprock(Enping Formation)of the source rock(Wenchang Formation)in the ZhuⅠdepression,the oil source faults throw of T70 boundary and the inter-layer distribution ratio of discovered oil and gas in fault-depression structure,we have studied the main control factors of near-source and far-source hydrocarbons accumulation in this area,and established a geological model manifesting the hydrocarbons migration through this regional caprock,hence carrying out the physical simulation experiment of hydrocarbons migration under different combinations of sand/formation ratio and fault throw.Statistics analysis shows that the lithologic association of the Wenchang Formation source rock and the Enping Formation direct caprock,as well as the fault development characteristics controlled the hydrocarbon accumulation in the structural layers of fault depression period(near-source)and the depression period(distal-source).Oil and gas mainly accumulate in the strata below the T70 boundary when the sand/formation ratio of Enping Formation is lower than 35%.When the sand/formation ratio is higher than 35%and the fault throw of oil source fault is over 100 m,it is conducive for hydrocarbons accumulating in the strata above the T70 boundary.The results of physical simulation experiment suggest that hydrocarbons migration and accumulation in the caprock are mainly controlled by the fault throw and the sand/formation ratio of caprock.The higher the sand/formation ratio and the larger the fault throw will lead to an easier hydrocarbons migration through the caprock.When the sand/formation ratio is 30%~50%,it is favorable for the hydrocarbons migration and accumulation inside the caprock.It is suggested to carry out a spatial-temporal matching relation evaluation on the lithologic association of source rock-overlying direct caprock and the fault development in subsags in combination with the simulation analysis of hydrocarbon generation history of source rocks,so as to provide references for accurately predict the main hydrocarbons accumulation combination and favorable exploration direction in this area.