Logging Classification and Recognition of Lacustrine Mixed Sedimentary Reservoirs in First and Second Members of Shahejie Formation in Bohai Sea

Mixed sedimentary reservoirs are widely developed in the first and second members of the Shahejie Formation in Bohai Sea, which is difficult to be identified the complex and diverse rock types. Based on the analysis of a large number of cores, sidewall cores, thin sections and whole rocks analysis, in this paper it systematically summarizes the logging characteristics of more than 10 kinds of mixed sedimentary reservoirs in six subclasses of two major types, and discusses the sensitivity of various conventional logging curves to the "composition" and "structure" of mixed sedimentary reservoir. The results show that the composition-structure two-level classification method not only has a good distinguishing effect on lithology identification but also on the quality of mixed sedimentary reservoir. Neutron and photoelectric absorption cross-section indexes are more sensitive to rock composition identification, while natural gamma, resistivity and neutron are more sensitive to rock structure identification. The logging identification method of mixed sedimentary reservoir based on composition-structure classification is simple, efficient and accurate, and has good application effect in practice. It provides insights into complex lithology identification and reservoir evaluation and classification, and has good application prospects in the lithologic identification of lacustrine migmatite reservoir in the first and second members of Shahejie Formation in Bohai Sea area and other areas under the similar geological background.