西非下刚果盆地Madingo组烃源岩地球物理综合评价

Geophysical Comprehensive Evaluation of Hydrocarbon Source Rocks of the Madingo Formation in the Lower Congo Basin,West Africa

下刚果盆地Madingo组海相烃源岩发育于海平面快速上升时期,Madingo组地层沉积速度极其缓慢,沉积厚度薄,沉积时间跨度大,属于典型的凝缩段沉积。以ΔlgR技术、GR曲线旋回分析法为手段,对照地球化学方法的研究结果对下刚果盆地烃源岩进行了研究。研究表明,下刚果盆地Madingo组烃源岩发育期与有机质的勃发期和最大海泛期相对应,发育3段富有机质硅质混合细粒岩相,其中Madingo组中段和上段为有机质富集段,有效烃源岩总厚度为200~600m,且干酪根类型多为Ⅰ型-Ⅱ1型,以倾油为主。

The marine hydrocarbon source rocks of the Madingo Formation in the Lower Congo Basin develop in the period of rapid rise in sea level. The deposition rate of this formation is extremely slow, and the sedimentary thickness is thin,corresponding with a long span of the deposition time. Madingo Formation belongs to a typical condensed section. In order to evaluate the quality of Madingo source rocks in vertical and horizontal directions, we used delta lgR technology and GR curve cycle analysis method successively, combining the methods of seismic facies and geochemistry. By using the delta lgR method, we analysed the acoustic and resistivity log and geochemistry of hydrocarbon source rocks TOC values by multiple linear regression model, and then obtained the calculation model of Madingo source rock TOC. Addionanally, by means of GR curve cycle analysis method, we evaluated the source rocks of the Lower Congo Basin under the framework of sequence stratigraphy theory, through the transgressive/regressive cycle division and the recognition of condensed section. The delta lgR analysisshows that the middle and upper section of the Madingo Formation is an organic enrichment section. The GR curve cycle analysis shows that the development stage of the hydrocarbon source rocks of Madingo Formation in the Lower Congo Basin corresponds well to organic blooming period and the maximum flooding period,with three sections of the rich organic silicon mixed fine-grained facies , belonging to rich organic section. The seismic facies and geochemistry research reveals that the thickness of effective source rock is 200--600 m,and most typical types of the kerogen are type I and lI 1 ,tending to generate oil. Overall, the Madingo Formation in the Lower Congo Basin developed good or excellent hydrocarbon source rocks.