Formation Conditions of Host Rocks and Veins of Productive Deposits of the Astrakhan Gas–Condensate Field

Abstract

One- (gas) and two-phase (aqueous solution plus gas) inclusions are studied in calcite taken from the Cheremshan horizon of the Bashkirian stage at a depth of 4215–4217 m in the Pravoberezhnaya-1 borehole. It is established that their homogenization temperatures are within 100–134°С, which is possibly close to the mineral formation temperature. Calcite veinlets were formed with the participation of a hydrocarbonate–calcium fluid enriched in magnesium chlorides. Inclusions in calcite mainly contain CO₂, CH₄, and H₂S. The gas composition of the inclusions in limestone differs in an elevated CO₂ content and the presence of CO with subordinate CH₄ and H₂S.