Evolution of the Thermal Cap in Two Wells from the Salton Sea Geothermal System, California

Abstract

The Salton Sea geothermal system is overlain by a thermal cap of low permeability rocks that restrict s the upward movement of the high-temperature reservoir brines. Petrographic and fluid inclusion data from two wells show that the thermal cap in the southern part of the field consists of an upper layer of lacustrine and evaporite deposits with low initial permeabilities and a lower layer of deltaic sandstones. The sandstones were incorporated into the thermal cap as downward percol at i ng fluids deposited anhydrite and calcite in the pore space of the rocks, reducing their permeabilities. During development of the thermal cap, basemetal sulfides, potassium feldspar and quartz veins were deposited by brines from higher temperature portions of the system.