Lithofacies types and reservoirs of Paleogene fine-grained sedimentary rocks Dongying Sag, Bohai Bay Basin, China

Abstract

Abstract By applying such technologies as detailed description of cores, identification of thin sections, X-ray diffraction analysis, and scanning electron microscopy, this paper establishes the lithofacies division scheme of the fine-grained sedimentary rocks in the Paleogene of the Dongying Sag, confirms the reservoir space types and characteristics of the major lithofacies, and analyzes the micro-structure characteristics of their pores. The research results show that: (1) the pore structure of the organic-rich laminated limestone facies is very complex, with multi-scale aperture. The micro-fractures connect the pores, and increase the porosity and permeability of reservoirs; (2) the pore structure of the laminated calcareous fine-grained mixed sedimentary facies with moderate organic content has not apparent multi-scale feature, but with better mesoporous opening property, poorer macroporous opening property, and ordinary connectivity of pores and fractures; (3) the reservoir space types of the organic-rich interbedded limestone facies are various, with stronger multi-scale aperture, better pore connectivity, apparent communication between pores and fractures, and the intercrystal pores and fractures in calcite recrystallization are the most important part of the macro-pores; (4) the reservoir space types of the organic-poor massive calcareous fine-grained mixed sedimentary facies are relatively simple, with undeveloped fractures, and poorer pore connectivity. By combining oil and gas generation potential, oil and gas flow ability, oil and gas reservoir properties and fracturing properties etc., the organic-rich laminated limestone and the organic-rich limy laminated fine-grained mixed sedimentary rocks are predicted as the favorable lithofacies.