Differential Diagenesis and Pore Evolution Characteristics of Different Sedimentary Microfacies Reservoirs of Bioclastic Limestone: A Case Study of MB2-MC1 Section in X Oilfield in The Middle East

Abstract

In order to clarify the differential diagenesis of different sedimentary microfacies of bioclastic limestone in Cretaceous M Formation in the Middle East and systematically analyze the characteristics of reservoir pore evolution, the data of regional geology, well logging, core, cast thin section, scanning electron microscope, three-dimensional CT and conventional porosity and permeability test are comprehensively used, taking MB2-MC1 section in X oilfield as an example, starting from the diagenesis and pore evolution of bioclastic-arene shoal, the characteristics of diagenesis of each sedimentary microfacies in different environments are analyzed, and the differential diagenesis, pore evolution process and its influence on physical properties are studied. It is showed that the reservoirs of MB2-MC1 section are mainly developed in the ramp shoal and platform margin shoal. The shoal facies can be further subdivided according to the type of bioclastic debris. The sedimentary microfacies determine the original fabric and bioclastic type of M Formation, and then control the diagenetic sequence and strength. Each sedimentary microfacies mainly experiences different degrees of mud crystallization and burrows in seawater environment, dissolution and cementation in atmospheric freshwater environment, compaction, pressure solution and dolomitization in burial environment. High energy microfacies have the characteristics of non-selective dissolution, mainly developing intergranular pores and intergranular dissolved pores. Medium energy microfacies have the characteristics of selective dissolution, mainly developing mould pores and intragranular pores. The medium-low energy microfacies have the characteristics of moderate cementation, moderate compaction and moderate-weak dolomitization, mainly developing intragranular pores and visceral foramen pores. The low energy microfacies have the characteristics of strong cementation, strong compaction and moderate dolomitization, mainly developing micropores, intercrystalline pores and visceral foramen pores, which are non-reservoirs.