The Pores Types, Genesis and Its Relationship with Reservoir Characteristics of Carbonate: Examples from Cretaceous Mishrif Formation Carbonate of West Qurna Oilfiled, Iraq

To classify pores and analyze pores genesis, make sense of the relationship between pore types and reservoir characteristics of carbonate. This study takes the Cretaceous Mishrif formation carbonate in West Qurna oilfield, Iraq, as examples. By means of thin section, physical properties, and mercury injection test of 421 samples, pores are classified as intraparticle, moldic, residual moldic, interparticle, micropore, and intercrystalline pore. According to dominated pore types, samples can be classified into six classes. They are classes of residual moldic, intraparticle, micropore, moldic, mixed pore, and interparticle pore. The pores genesis is controlled by sedimentary environment and diagenesis. Pore types are determined by lime mud contents, bioclastic textures, types and abundance, and the latter were controlled by sedimentary environments. The pores generation is mainly dominated by dissolution, which is influenced by mineralogy composition of bioclastic. Besides, pores were altered by micritization, cementation, and compaction. It is found that the dominated pore types are closely related to reservoir characteristics. Each class of samples corresponds to two or more rock types and bioclastic types, while the physical properties and pore structure are similar, respectively, which reveal that pore types are a key factor of strong heterogeneity.