Reservoir Processes Inferred by Geochemical, Stable Isotopes and Gas Equilibrium Data in Cerro Prieto, B.C., MÈxico

Abstract

Based on hydrogeochemical, stable isotopes data and the chemical equilibrium of the Fischer-Tropchs reaction (Giggenbach methodology), the interaction of the aquifers, and the reservoir process were studied. Additionally, gas equlibria methods involving Fischer-Tropsch-Pyrite-Magnetite; and Fischer-Tropsch-Pyrite-Hematite-Pyrite-Magnetite reactions also were used in order to define if these approaches may be applied to evaluate reservoir temperature and mass steam fraction in the new Cerro Prieto IV area.
Boiling process was identified for CP-III, while excess steam is found absent in CP-II. Instead, a deficit of vapor is seen, particularly in the W part of CP-II and in the SE part of CP-I. These facts may be related to the evaporated brine injection and the entry of the groundwater. The distribution of temperature calculated by tccg shows a thermal gradient of the beta fluid that increase in east direction, where CP-II temperatures are higher than CP-III.
Gas equlibria methods (involving Fischer-Tropsch-Pyrite-Magnetite; and Fischer-Tropsch-Pyrite-Hematite-Pyrite-Magnetite reactions) were applied in some selected producing wells from four areas under exploitation. The results show good correlation for both equilibria methods; however Fischer-Tropsch Pyrite-Magnetite reactions provide the best estimation of the physical reservoir parameters. The main processes found for Cerro Prieto IV area are lateral vapor contribution and the inflow of hotter and deeper fluid with high liquid saturation.