Abstract:

In order to find out the response of diagenesis to hydrocarbon fluid flowin the Third Member of Shahejie Formation in central uplift belt of Dongying depression,the relationshipbetween the formation of authigenic minerals and hydrocarbon fluids flow were analyzed based on the results of microscopic observation, inclusion thermometry, scanning electron microscope and cathode luminescence.the diagenetic sequence is: the first period of quartz overgrowth→the first period of carbonate cements（pyrite particles）→a layer of chlorite film→the second period of carbonate cements→the second period of quartz overgrowth（the first period of kaolinite）→the third period of carbonate cements→ the third period of quartz overgrowth（the second period of kaolinite）→the fourth period of ferric carbonate cements（pyrite particles）. The first hydrocarbon filling occurred duringthe later stage of the second period of carbonate cements formation. The second and third hydrocarbon filling occurred duringthe mid-to-late stage of the third period of carbonate cements formation. The formation of the fourth period of carbonate cements representsthe end of large-scale hydrocarbon filling. Hydrocarbon fluid has great impact on the formation of three types of authigenic minerals in the study area, including authigenic kaolinite, ferric carbonate minerals and pyrite. In the sandstone reservoir, the activity of hydrocarbon fluid can be identified by various diagenetic phenomena, such as embayed corrosion of the second and the third period of carbonate cements, large growth of kaolinite, and paragenetic association of the fourth period of carbonate cements and the pyrite. In the sandstone strata with high oil saturation, hydrocarbon fluid may lead to large-scale corrosion of carbonate cements and the corrosion of feldspar, which causeagreat formationof kaolinite. In addition, paragenetic association of ferric carbonate cements and pyrite can be observed at the interface of sandstone and mudstone. However, in the strata with low oil saturation or oil-free, due to lacking of organic acid provided by hydrocarbon fluid, kaolinite is less developed, and the early period of carbonate cements is well preserved.

Key words: diagenesis, hydrocarbon fluid, the Third Member of Shahejie Formation, central uplift belt, Dongying depression