Low-permeability reservoir types classification and reservoir sensitivity controlling factors: a case study of Paleogene in Bohai Sea

Through the identification of thin sections, SEM analysis, sensitivity experiment of reservoirs and other analytical methods, this paper subdivides the types of low-porosity and low-permeability reservoirs in Bohai Sea, conducts a detailed study on the reservoir sensitivity of various reservoir-developed intervals and the characteristics, content and distribution of the corresponding clay minerals, and analyzes the effects of different sedimentary conditions on reservoir sensitivity. The results show that the low-permeability reservoirs in Bohai Sea are classified into kaolinite-rich type, illite-rich type, chlorite-rich type and carbonate dense cementation type. By establishing the relation between the genesis of low-permeability reservoirs with reservoir sensitivity, it is proposed that reservoir sensitivity is mainly controlled by three factors: parent rock type, paleoclimate conditions and sedimentary microfacies. First, parent rock type has a decisive influence on the evolution of the Paleogene clastic reservoirs in the study area. There are three main types of parent rocks, i.e., clastic reservoirs with intermediate-basic volcanic rocks as parent rocks, pyroclastic-kaolinite type of clastic reservoirs with intermediate-acidic volcanic rocks as parent rocks, and illite type of clastic reservoirs with metamorphic rocks as parent rocks. Paleoclimatic conditions have a vital impact on reservoir sensitivity. Sedimentary microfacies have a direct influence on the differentiation of clay minerals is directly affected and an indirect influence on the late diagenesis. © 2019, Editorial Office of ACTA PETROLEI SINICA. All right reserved.