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MODELING OF RESERVOIR FORMATION IN SILICEOUS LIMESTONES UNDER THE INFLUENCE OF HYDROTHERMAL FLUIDS (SERIES WITH H2O2, HCL AND SALTS)

M. Yu. Zubkov

West-Siberian Geological Center, Tyumen, Russia

The results of modeling the formation of secondary reservoirs (hydrothermal silicites) in siliceous limestones with a wide areal distribution in the pre-Jurassic complex of Western Siberia, exposed to hydrothermal fluids in the H2O-H2O2, H2O-HCl and H2O-salt systems are considered. Experiments with the hydrogen peroxide were carried out at temperatures of 295 and 390°C and H2O2 concentrations from 29 to 43%. Experiments with hydrochloric acid were carried out at a temperature of 410°C, and its concentration varied from 0.05 to 1.0N. Experiments with salts were carried out at a temperature of 400°C, CO2 concentration of 0.48 g / l and a salt content of 36.8 g / l NaCl and 3.1 g / l CaCl2. It was found that in the first system (Н2О-Н2О2), metals that compose the autoclave take an active part in reactions of hydrothermal synthesis, that, to a certain extent, complicates the study of resulting mineral associations. Hematite, anhydrite, native sulfur and sulphates, as well as chromium and nickel oxides are the newly formed (hydrothermal) mineral phases in this system. Dolomite, pyrite and calcite are unstable initial minerals. Dolomite, calcite, and pyrite are also unstable minerals in the water-hydrochloric acid system, and the formation of new (hydrothermal) associations depends on the acidity of the fluid: the stable association is the kaolinite-siderite one under ultra-acidic conditions, and chlorite is formed in more alkaline conditions. Acid feldspar, zeolite, wollastonite and sodium-calcium carbonates are formed in the water-salt system. Pyrite, dolomite, calcite, illite and partially biogenic quartz are decomposed. In all experiments, the formation of secondary porosity was observed due to the dissolution of unstable minerals. It is determined that forming secondary pores are very small in size, which leads to a high content of residual water in these secondary reservoirs. The main regularities of the secondary reservoirs formation – hydrothermal silicites - are revealed by Paleozoic siliceous limestones.

Keywords: siliceous limestones, hydrothermal fluids, systems, Н2О–Н2О2, Н2О–НСl, H2O–salts, secondary reservoirs, hydrothermal silicites.

DOI 10.20403/2078-0575-2021-1-32-48