东非M盆地福拉凹陷烃源岩及原油地球化学特征

Source rock evaluation and crude oil geochemi-stry in the Fula Depression, M-Basin, East Africa

Fu 1井为东非M盆地福拉凹陷的区域探井 ,获高产油流。分析Fu 1井与Bal 1井烃源岩地球化学特征 ,下白垩统AbuGabra组中段烃源岩为低熟—成熟的好—极好烃源岩 ,推测埋藏较深部位的烃源岩成熟度较高 ,资源潜力较大 ,认为福拉凹陷是M盆地最好的生油凹陷。Fu 1井的原油为成熟度不高的成熟原油 ,遭到生物降解的影响 ,但饱和烃中异构烷烃含量高、正构烷烃序列完整 ,据推测油藏经历两期充注 ,原油的三环萜烷和甾烷含量较低 ,C2 9TS含量高 ,重排藿烷系列完整 ,含有一定量的γ 蜡烷 ,升藿烷系列中 2 2S构型大于 2 2R构型 ,甾烷系列中的重排甾烷含量高 ,C2 7、C2 8、C2 9甾烷呈反“L”型分布 ,含有丰富的 4 甲基甾烷 ,成油母质为陆源有机质与水生生物混合输入 ,沉积水体为淡水—微咸水介质。图 5表 3参

The Well Fu 1 is a regional exploration well in Fula Depression, M Basin, in which the high production commercial oil was obtained. The geochemistry character of the Well Fu 1 and Bal 1 suggests that the horizon developed in the middle interval of the Abu Gabra Formation is the low matured good to excellent source rock.It is supposed that the hydrocarbon source rock in the deeper could be higher mature. The source rock in the Fula Depression is the best strata in M Basin with greater resource potential. The thermal evaluation of hydrocarbon source rock in this well is at a low mature stage.The crude oil had been affected by biodegradation, but it's saturated hydrocarbon has a high percentage of isoporaffin and an entire sequence of n alkane. It is supposed that the reservoir was filled twice. The crude oil has tricyclic and sterane,high C 29 Ts,an entire sequence of diasterane and some γ cerane. In the series of homohopane, the 22S configuration is bigger than 22R configuration. About the series of sterane, it has high diasterane; the C 27 , C 28 , and C 29 sterane distributed in a dissymmetry “L” style. The depositional water is fresh water little salt water.