Abstract
The dolomite in dolomitic glutenite of the shahejie formation in the eastern steep slope of the Shijiutuo bulge in Bohai is a high-quality reservoir, and the content of dolomite is positively correlated with reservoir physical properties. In this paper, by using thin section, core, wall core, geochemical data and analyzing petrology and mineralogy characteristic, we systematically analyzed the paleogeographic environment and genetic mechanism of this kind of dolomite and established the genetic models. The dolomite in the glutenite body has many characteristics of development, which is formed by three kinds of genesis: quasi-synergy dolomitization, buried dolomitization and hydrothermal dolomitization. The dolomite in glutenite is produced in the form of matrix, grain (sandstone, oolith), biological skeleton (conch, ostracod), clastic shell and dolomite cement. The minor elements, carbon and oxygen isotopes, trace minerals and paleontological combinations reveal that the paleogeographic environment was closed continental salt-brackish water bay, the climate was arid and hot, and the evaporation was strong. It provides favorable conditions for the production of the dolomite in dolomitic glutenite. There are three genetic models of dolomite. The first model is penecontemporaneous dolomitization. The climate was arid and hot, the aragonite and high-magnesium calcite deposited with sand and gravel. Due to the effect of evaporation, dolomitization occurred. The second model is buried dolomitization. The water from dehydration of clay minerals causes the Mg2+ in the high-magnesium formation migrating into the rock, leading to the occurrence of dolomitization. The third model is hydrothermal dolomitization. Deep faults can bring geothermal fluids into the overlying reservoir and form the hydrothermal dolomite.
Highlights
Dolomite as a good reservoir in carbonate rocks is an important target of oil and gas exploration
The dolomite in dolomitic glutenite of the shahejie formation in the eastern steep slope of the Shijiutuo bulge in Bohai is a high-quality reservoir, and the content of dolomite is positively correlated with reservoir physical properties
The water from dehydration of clay minerals causes the Mg2+ in the high-magnesium formation migrating into the rock, leading to the occurrence of dolomitization
Summary
Dolomite as a good reservoir in carbonate rocks is an important target of oil and gas exploration. The dolomitic glutenite reservoir with high oil production was discovered in the Shahejie formation of the eastern steep slope of the Shijiutuo bulge in the Bohai Sea. For the lacustrine dolomite reservoir characteristics, diagenesis, paleogeographic environment and control factors, many research findings have been carried out by the predecessors. The research on the genetic mechanism of dolomite in the dolomitic glutenite is lacking, especially in the Bohai Sea. In this paper, the dolomitic glutenite of the Shahejie formation in the eastern steep slope of the Shijiutuo bulge is the main research object. The petrology and mineralogy analysis, the formation and sedimentary environment of dolomite, and the genetic model are established. It has guiding significance for the study of the genesis of dolomite in lacustrine carbonate reservoir
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