东非海岸盆地下侏罗统沉积特征及其控源作用

下侏罗统烃源岩是东非海岸盆地的主力烃源岩。利用钻井、测井、地震及地球化学分析化验等资料，结合区域构造演化，对东非海岸盆地下侏罗统的沉积特征进行了分析和描述，并结合其烃源岩发育特征，对烃源岩的成因模式及其主控因素进行了刻画和评价。研究结果表明：①东非海岸盆地早侏罗世受区域构造作用影响，形成了狭长而闭塞的海湾沉积环境，发育河流-三角洲-滨浅海-局限海或浅海沉积体系；②下侏罗统发育的局限海相泥岩为盆地内的优质烃源岩，其TOC平均为4.2%，有机质类型以Ⅰ—Ⅱ₁型为主，已达成熟—过成熟演化阶段，泥岩厚度大且分布广，生烃潜力大；主力烃源岩的发育与展布受其独特的海湾沉积环境影响，由北向南盆地主力烃源岩的质量及生烃潜力逐渐变好；③东非海岸盆地发育局限海相沉积型、潟湖相沉积型和三角洲相沉积型3种烃源岩成因模式，其中局限海相沉积型烃源岩是盆地优质烃源岩的主要成因类型，岩性以稳定分布的厚层泥岩为主，夹薄层砂岩，总体评价为好烃源岩；④东非海岸盆地最有利的生烃区带位于鲁伍马盆地和坦桑尼亚盆地深水沉积的中心区域。该研究结果可为东非海岸盆地的油气勘探指明方向。

Sedimentary characteristics and source control of Lower Jurassic in coastal basins of East Africa

The Lower Jurassic source rocks are the main source rocks in the coastal basins of East Africa. Based on the data of logging, drilling, seismic and geochemical analysis, combined with regional tectonic evolution, the sedimentary characteristics of the Lower Jurassic in the coastal basins of East Africa were analyzed and described, and the genetic model and main controlling factors of the main source rocks were characterized and evaluated by considering the characteristics of source rocks in the basins. The results show that:(1)The sedimentary environment of narrow and long occluded bay was formed by regional tectonism in the Early Jurassic in the coastal basins of East Africa,and the sedimentary systems of river,delta coastal shallow sea,confined sea or shallow sea were developed.(2)The limited marine mudstone developed in the Lower Jurassic is the high-quality source rocks of the basins,with an average TOC of 4.2%. The organic matters are mainly type Ⅰ-Ⅱ₁,which has reached mature to over mature evolution stage. The mudstone is thick and widely distributed,and has great hydrocarbon generation potential. The development and distribution of main source rocks are affected by its unique sedimentary environment of bay,and the quality and hydrocarbon generation potential of main source rocks in the basins gradually improve from north to south.(3)There are three genetic models of source rocks in the coastal basins of East Africa:restricted marine sedimentary type,lagoon sedimentary type and delta sedimentary type. Among them,the restricted marine sedimentary source rock is the main genetic type of high-quality source rocks. The lithology is mainly composed of stably distributed thick mudstone and intercalated with thin sandstone,which is generally evaluated as good source rocks.(4)The most favorable hydrocarbon generating zones are located in the central areas of Rovuma Basin and Tanzania Basin on the coast of East Africa. The research results can provide reference for the next exploration and development of coastal basins in East African.