乍得Bongor盆地储层沉积成岩特征及其主控因素

Sedimentary-Diagenetic Characteristics of Reservoir Sandstone and Their Controlling Factors in Bongor Basin,Chad

乍得Bongor盆地储层沉积成岩特征具有明显的独特性。结合盆地区域构造演化,利用地震、钻井、岩心、薄片、测试等资料,系统分析了Bongor盆地主力储层沉积展布特征和成岩演化。研究结果表明:Bongor盆地早白垩世强烈拉张裂陷作用形成了一系列NW-SE向深陡凹陷,主力储层局限分布在凹陷内部,以近岸水下扇沉积为主,毗邻控凹断层分布,具有近源、深水、快速沉积特征,结构成熟度和成分成熟度均较低;受多期构造运动及烃类流体改造,储层压实作用不充分,胶结成岩作用减弱,溶蚀现象普遍,目前尚处于中成岩A期阶段;以原生孔隙为主,属中孔、中高渗储层,有效储层埋深下限明显大于现今油层深度,表明盆地深层仍发育有优质储层,具有良好的勘探潜力。

The sedimentary and diagenetic characteristics of reservoir were special in Bongor basin,Chad.Based on regional tectonic evolution and various basic data such as cores,thin sections,mud logging,test data and so on,the authors do systematic research on the sedimentary-diagenetic characteristics of reservoir sandstone.The results show that series of NW-SE depressions were formed during the early Cretaceous rifting stage by the NE-SW extension,which controlled the sediment source,the sandstone distribution patterns and formed lots of fans.These fans should be classified as subaqueous fans and mainly distributed along the boundary faults.The structure inversion of the Late Cretaceous induced large amount of erosion and uplifted the reservoir greatly.It also influenced the normal diagenesis process of the reservoir.Due to the tectonic evolution,the hydrocarbon infilling and compositional maturities,their mechanical compaction and cementation were relatively weak but the dissolution was relatively common.The diagenesis of reservoir sandstone was still under the substage of the middle diagenetic stage and has the good quality： medium porosity,medium-high permeability.The quantitative evaluation of the relationship between porosity and burial depth revealed that the depth limit of the effective reservoirs is much deeper than that of the present oil pay zones and the deep reservoir still has a good prospect of exploration.