SEDIMENTARY AND DIAGENETIC CHARACTERISTICS OF PALEOGENE LACUSTRINE FINE-GRAINED HYBRID SEDIMENTARY ROCK IN DONGYING SAG

It needs to be further studied including the lithofacies types, diagenetic evolution and pore and fissure development mechanism of Paleogene lacustrine fine-grained hybrid sedimentary rock in Dongying Sag. By means of core observation, thin section, X-ray whole rock diffraction, carbon and oxygen isotope analysis, the fine-grained mixed sedimentary facies types and diagenetic characteristics are clarified, and the formation of overpressure, microfracture development, carbonate dissolution, calcite vein generation, etc. are expounded Diagenetic events closely related to fracture development. The results show that the fine-grained hybrid sedimentary rock in the study area can be divided into four lithofacies: felsic fine-grained hybrid sedimentary rock, clayey fine-grained hybrid sedimentary rock, carbonate fine-grained hybrid sedimentary rock and clay bearing felsic fine-grained hybrid sedimentary rock. It is confirmed that the argillaceous calcite occuring in the hybrid sedimentary rock mainly belongs to the carbonate related to the biogas generated by methane bacteria activity. The lenticular and lamellar sparry calcite lamina are derived from vein calcite filling microfractures, and the microfractures and calcite veins are concentrated in the early sub dry gas oil generation stage. It reveals the whole syngenetic evolution mechanism from hydrocarbon generation pressurization, microfracture formation, organic acid expulsion, thermal evolution of organic matter, dissolution of micritic calcite, recrystallization of calcite and vein formation, to the influence of cementation of adjacent sandstone bodies.The whole process has important guiding significance for the study of shale oil and gas reservoir formation in middle and deep layers.