Abstract: Thick bioclastic limestone reservoirs are developed in the Cretaceous Mishrif Formation of the M oilfield in the Middle East, and there are some fators constraining the reservoir development, such as interlayer uneven liquid production and low producing reserves degree. To deepen the understanding of the internal heterogeneity of carbonate reservoirs, based on core observation and description, casting thin sections, physical property analysis, mercury injection experiment and logging data, a study is performed on the type, origin and distribution of interlayers in Mishrif Formation. The results show that the interlayers in Mishrif Formation can be divided into 3 categories (sedimentary type, diagenetic type and coal-forming type)and 5 sub-categories (lagoon sedimentary type, deep-water sedimentary type, weathering cementation type, lagging cementation type and lagoon-exposed type). The lagoon sedimentary type and deep-water sedimentary type were developed in low-energy lagoons and open shallow seas, respectively, with high shale content and low primary permeability; they are classified as lithologic interlayers. The weathering cementation type were developed in alternate environments with arid and humid climates. The sea level fell significantly, and the strata were exposed for a long time. Under the weathering and leaching, a breccia zone was formed. Dense cementation occurs to saturated fluids in fractures, forming permeability barrier. The lagging cementation type were developed in high-energy shoals. The upper part of the shoal underwent leaching and dissolution, and the bottom was cemented to form a compact zone. The interlayers are small in thickness, and are not easy to be found. The lagoon-exposed type was developed in a warm and humid climate; the lagoon was exposed for a long time and peatification occurred. Through fine rock-electricity calibration, this paper establishes logging identification standards and discrimination methods for different types of interlayers, and clarifies the spatial distribution of interlayers in thick reservoirs in Mishrif Formation. The lagging cementation type and lagoon sedimentary type were developed in Mishrif Formation, while the deep-water sedimentary type was only developed in the MB2.2 layer, the weathering cementation type was only developed on the top of Mishrif Formation, and the lagoon-exposed type was only developed on the top of the MB2.1 layer. The development type and distribution characteristics of interlayers are controlled by such factors as sedimentary environment migration, eustatic cycles, exposure time of sediments and climate conditions.

Key words: bioclastic limestone, interlayer, lagoon, cementation, Mishrif Formation, Cretaceous

摘要： 中东地区M油田白垩系Mishrif组厚层生物碎屑灰岩油藏存在层间产液不均衡、储量动用程度低等开发矛盾。为深化碳酸盐岩油藏内部非均质性认识，基于岩心与岩石薄片、测井资料和孔隙度、渗透率、压汞实验等测试资料分析，对Mishrif组隔夹层的类型、成因及展布规律进行研究。Mishrif组发育沉积型、成岩型和成煤型3类隔夹层，包括潟湖沉积型、深水沉积型、风化胶结型、滞留胶结型和潟湖暴露型5个亚类。潟湖沉积型和深水沉积型隔夹层分别发育于低能潟湖和开阔浅海，其泥质含量高，原始渗透率低，属于岩性隔夹层。风化胶结型隔夹层发育于干旱气候与湿润气候交替的环境，海平面大幅度下降，地层长时间暴露，风化作用和淋滤作用耦合形成角砾岩带，饱和流体在缝隙中发生致密胶结形成物性遮挡。滞留胶结型隔夹层发育于高能浅滩，滩体上部发生淋滤溶蚀、底部发生胶结作用形成致密带，隔夹层厚度较小、隐蔽性强。潟湖暴露型隔夹层发育于气候温暖湿润的环境，潟湖长期暴露并发生泥沼化作用。通过岩-电精细标定，建立了不同类型隔夹层的测井识别标准和判别方法，明确了Mishrif组厚层油藏内部隔夹层的空间展布规律。Mishrif组主要发育滞留胶结型和潟湖沉积型隔夹层，深水沉积型隔夹层仅发育于MB2.2层，风化胶结型隔夹层仅发育于Mishrif组顶部，潟湖暴露型隔夹层仅发育于MB2.1层顶部。沉积环境迁移、海平面升降旋回、暴露时间和气候条件等因素控制了隔夹层的发育类型与分布特征。

关键词: 生物碎屑灰岩, 隔夹层, 潟湖, 胶结作用, Mishrif组, 白垩系