利比亚锡尔特盆地油气地质特征及有利区带预测

锡尔特盆地是利比亚最重要的含油气盆地,属北非克拉通内裂谷盆地。盆地演化经历了3个阶段:早古生代克拉通边缘坳陷、早白垩世--晚始新世裂谷和渐新世以后的坳陷阶段。发育下白垩统、上白垩统和古近系3套主要的烃源岩,其中上白垩统锡尔特页岩是最主要的烃源岩;储集层分布于基底至古近系渐新统的各个层段,前白垩系储层以碎屑岩为主,上白垩统及其上储层以碳酸盐岩为主;盖层主要为上白垩统和古近系下始新统页岩、泥灰岩和蒸发岩。受北西-南东向正断层控制,形成了一系列与断层走向一致的地垒和地堑,对应于3个大致平行的地垒隆起,可划分出西部、中部和东部3个油气聚集带,纵向上可以划分出前地堑和地堑充填阶段两大套含油层系。综合评价认为,盆地具备3类油气勘探的有利区:Ⅰ类区位于地垒带,Ⅱ类区位于地堑带,Ⅲ类区位于盆地北部海域。

Petroleum geologic characteristics and play prediction in the Sirte Basin,Libya

Sirte Basin,an intracratonic rifted basin in North Africa,is the most important petroliferous basin in Libya.It has experienced three stages of evolution:the Early Paleozoic eratonic margin depression,the Early Cretaceous-Late Eocene rift and the post-Oligocene depression.Three sets of source rocks were developed :the Lower Cretaceous shale,the Upper Cretaceous shale and the Paleogene shale,of which the Upper Cretaceous Sirte Formation shale is the main source rock.Reservoirs occur at various horizons from the basement to the Oligocene. The Pre-Cretaceous reservoirs are dominated by clastic rocks,while the Upper Cretaceous reservoirs and their overlying reservoirs mainly consist of carbonate rocks.Cap rocks are mainly the Upper Cretaceous and Lower Eocene shale,marl and evaporite.A series of horsts and grabens in parallel with the faults were developed under the control of the NW-NE-trending normal faults.Laterally,three hydrocarbon accumulation zones in correspondence with three roughly parallel horst uplifts were recognized:the western,central and eastern zones.Vertically, two oil-bearing sequences were recognized:the pre-horst and horst fillings.According to the above analysis,three types of favorable plays occur in the Sirte Basin:type Ⅰ in the horst zone,type Ⅱ in the graben zone and type Ⅲ in the northern offshore area.