辫状河厚砂层内部夹层表征——以大庆喇嘛甸油田为例

Characterization of interlayers within braided-river thick sandstones:A case study on the Lamadian Oilfield in Daqing

以大庆喇嘛甸油田葡Ⅰ组PⅠ23砂层为研究对象,在单井夹层识别基础上,将辫状河厚砂层层内夹层分为单砂体间夹层和单砂体内夹层。单砂体间夹层发育于两期河道砂体叠置区域,为泛滥平原细粒沉积,河道底部滞留泥砾隔挡层,以及废弃河道充填;而单砂体内夹层主要包括心滩坝内部落淤层、坝间泥岩和串沟充填等。在连片分布厚砂层中划分单期河道砂体,从而揭示了单砂体间夹层的展布。在前人现代沉积及露头研究指导下,多井对比预测出心滩坝内部构型界面展布,并在内部界面约束下采用随机模拟方法建立了心滩坝内部夹层三维模型,坝内夹层分布零散,连续性差。在单砂体间夹层及心滩坝内局部有一定规模夹层的分割作用下,可以形成相对剩余油富集区。

Taking the PI23 sand layer in the Lamadian Oilfield,Daqing as a study example,we divided interlayers within thick braided-river sand beds into two different types,single-sandbody interface layers and single-sandbody intra-interlayers based on the identification of interlayers in individual wells.The former interlayer commonly develops in a region superimposed by two-phase channel sandbodies and is composed mainly of floodplain fine-grain deposits,mud-gravel impermeable barriers that are resorted at channel bottom,and abandoned channel fillings.While the latter interlayer is dominated by falling silty seams inside mid-channel bars,interbar muds and chute fillings.Moreover,the identification of single-phase channel sand bodies in uninterruptedly distributed thick sand layers revealed the distribution of single-sandbody interface layers.Guided by previous studies on modern deposits and outcrops,we predicted the distribution of inner architecture surfaces within mid-channel bars through multiple wells correlation,and accordingly established a 3D model of inner interlayers of mid-channel bars under control of internal architecture surfaces by stochastic modeling,which demonstrated a discontinuous distribution of and a poor consistency between inner interlayers in mid-channel bars.Therefore,a zone relatively enriched in remaining oils could be formed under the partition of single-sandbody interface layers and local interlayers on a considerable scale inside mid-channel bars.