Fluid inclusions in vein calcite from the productive reservoirs of the Astrakhansky gas condensate field

Abstract

© 2020 IOP Publishing Ltd. All rights reserved. Fluid inclusions from calcite veins were studied the Astrakhanskoye gas condensate field. It was done for the identify the conditions for the formation of oil reservoirs located in bioclastic recrystallized limestones with vertically oriented fractures. Samples were selected from the core material of one studied well in interval 4215-4217 m. Two types of syngenetic inclusions were found in calcite: gas and gas-liquid inclusions. The homogenization temperature of gas inclusions is from -16.9 to 40 °C. Studying the gas phase by Raman spectroscopy show the presence of methane and hydrogen sulfide. Carbon dioxide, ethane, and propane were found in smaller quantities. The homogenization temperature is 100-130 °C of two-phase fluid inclusions. Probably, it is close to the temperature of the vein calcite aggregates. The aqueous phase of inclusions is represented by solutions of magnesium chloride. The gas-phase was not studied by Raman spectroscopy because of mobility. The total composition of inclusion gases in calcite is represented mainly by carbon dioxide, methane, and hydrogen sulfide, according to gas chromatography. Ethane, propane, and isobutane are present in smaller amounts. The concentration decreases from ethane to butane. Also, ethylene, propylene, and butylene were identified in very low concentrations. A characteristic feature of hydrocarbon gases is a decrease in concentrations from ethane to propane and from propane to butane, and it is typical for gas condensates.