下刚果盆地早白垩世Pointe Indienne组湖相浊积岩特征及石油地质意义

Characteristics and hydrocarbon significance of lacustrine turbidite of Early Cretaceous Pointe Indienne Formation in Lower Congo Basin

为了明确下刚果盆地盐下重点勘探层系,采用沉积学、石油地质学的相关理论和方法,结合区域地质背景、钻测井数据和分析测试结果等资料,对下刚果盆地早白垩世Pointe Indienne组湖相浊积岩特征及其石油地质意义进行了探讨,并建立了Pointe Indienne组大型浊积扇的发育模式。结果表明:该浊积岩形成于深湖相沉积环境,其叠置砂体具有典型的浊流沉积特征,发育典型的鲍玛序列及特征沉积构造;该浊积砂岩为长石岩屑质石英砂岩或杂砂岩,其成分成熟度低、结构成熟度较差,表现为快速堆积的重力流沉积特征;该浊积砂岩内部识别出了多套完整和不完整的鲍玛序列,显示了厚层块状浊积岩和薄层或微层浊积岩的组合形式,指示了浊积扇内扇、中扇、外扇的沉积特征;该浊积砂岩为中孔低渗储层,与Pointe Indienne组上段和下段发育的厚层优质烃源岩接触,具有良好的生、储、盖组合,是下刚果盆地盐下油气勘探的重点层系。

In order to define the key subsalt exploration layer in the Lower Congo Basin,the characteristics and hydrocarbon significance of lacustrine turbidite of Early Cretaceous Pointe Indienne Formation in the Lower Congo Basin were investigated by using the relevant theories and methods of sedimentology and petroleum geology,combined with regional geological background,drilling and logging data and the test analysis results,and the development model of large turbidite fan of Pointe Indienne Formation was established.The results show that the turbidite was formed in the deep lake sedimentary environment,and its superimposed sandbody has typical turbidite sedimentary characteristics,such as typical Bauma sequence and characteristic sedimentary structure.The turbidite sandstone is feldspathic detrital quartz sandstone or greywacke with low component maturity and poor structural maturity,which is characterized by rapid accumulation of gravity flow sedimentation.A number of complete and incomplete Bauma sequences have been identified in the turbidite sandstone,showing the combination of thick massive turbidite and thin or micro turbidite,indicating the sedimentary characteristics of the inner,middle and outer fans of the turbidite fan.The turbidite sandstone is a medium porosity and low permeability reservoir,which is in contact with the thick and high-quality source rocks developed in the upper and lower part of Pointe Indienne Formation.It has good source reservoir cap assemblage,and is the key layer for the subsalt oil and gas exploration in the Lower Congo Basin.