库车坳陷白垩系巴什基奇克组露头储层特征

巴什基奇克组露头储集岩主要为中粒岩屑砂岩,孔隙类型以次生的杂基内溶蚀微孔为主,强-中等胶结、弱-中等溶蚀成岩相最为发育。巴什基奇克组存在着3种砂体成因类型:一是分布于该组二段的辫状三角洲平原砂质辫状河道砂体;二是分布于该组一段的辫状三角洲平原砾质辫状河道砂体;三是分布于该组三段的扇三角洲储集体。在储层砂体原型模型的基础上,将巴什基奇克组的储层建筑结构划分为6级层次界面和6级层次实体,储层骨架结构属于“积木式”。单砂体多呈板状和宽透镜状。与井下巴什基奇克组储层相比,露头区砂体的粒度要粗一些,碳酸盐胶结物含量要高一些,储集性能也要差一些。造成两者之间存在明显差异的原因是露头储层经历了表生成岩作用的改造。

RESERVOIR CHARACTERISTICS IN CRETACEOUS BASHIJIQIKE FORMATION OUTCROP IN KUQA DEPRESSION

Reservoir rocks in Bashijiqike Fm outcrop are mostly of medium-grained lithic sandstone, dominated by the secondary dissolved micropores, strong-medium cementation, and weak-medium dissolved diagenetic facies. There are three genetic types of sand bodies in the Bashijiqike Fm, including sandy-braided channel sand bodies in the braided-delta plain in the 2nd member of Bashijiqike Fm, gravel-braided channel sand bodies in the braided-delta plain in the 1st member of Bashijiqike Fm,and fan delta reservoir sand bodies in the 3rd member of the Fm. On the basis of reservoir sand bodies' prototype-model, the reservoirs' architectural structure of Bashijiqike Fm outcrop can be divided into 6-grade hierarchical interfaces and 6-grade hierarchical entities, and the framework structure is of “building block” pattern. Single sand body occurs generally as tabular mass or wide lens.By contrasting with those in the subsurface,sand bodies in the outcrop area might be a little bit coarser,with higher cement content,and worse reservoir quality.The obvious differences between them might be caused by the epidiagenesis in the outcrop.