乍得BNE区块P组油藏层序格架及对油藏的控制作用

Reservoir sequence framework and its control effects on reservoirs of P formation in Chad BNE block

乍得Bongor裂谷盆地由于其晚期的构造反转,在层序的形成上具有独特性,导致盆地内BNE等油藏平面与纵向非均质性较强,而盆地内取心资料少,加大了建立油藏层序格架的难度。结合区域构造演化,分析各级层序成因,利用地震、钻井、岩心、测试等资料在层序地层学思想指导下建立各级层序与层组的对应关系,识别层序界面,在三级层序框架下构建能反映油藏层间差异性的四级层序。研究结果表明:各级层序受构造沉降和全球海(湖)平面变化双重作用,BNE油藏各砂层组受长米兰科维奇旋回影响对应于四级层序,层序界面顶部为低密度、高声波时差油页岩,井震结合方法在该油藏取心资料匮乏的情况下能较好地识别此级别层序界面并进一步划分地层,在层序格架控制下,各油水层横向分布和产能差异较大,故建立目的层层序格架对多期叠置砂体油藏分层系高效开发具有重要意义。

Bongor rift basin in Chad,due to its late tectonic inversion,has the unique characteristics in the formation of sequence,which leads to the strong plane and vertical heterogeneity of BNE reservoir and other reservoirs in the basin.The prerequisite of implementing the reservoir characteristics is to establish the reservoir sequence framework.Combining with regional structural evolution,analyzing sequence origin at all levels and using seismic,drilling,core,test and other data,the author established the correspondence between the sequence and bed set of each order under the guidance of sequence stratigraphy,the sequence interfaces can be identified and a 4-order sequence can be constructed under 3-order sequence framework,which can reflect interlayer difference in reservoirs.The results of the study showed that all sequences were affected by tectonic subsidence and global sea(lake)level changes.The sand groups in BNE reservoir correspond to a 4-order sequence due to the effects of long Milankovitch cycle.The top of the sequence interface is oil shale with low density and high interval transit time.The well-seismic combining method can better identify this order of sequence interface and further divide the strata in the case of the lack of reservoir coring data.Under the control of sequence framework,the lateral distribution and production capacity of each oil and water layer differ greatly.So it is of great significance to establish the target sequence framework for the efficient development of the stratification systems of multi-stage superimposed sandstone reservoir.