Major geochemical processes in the evolution of Eocene carbonate aquifer, Kuwait

The Eocene Dammam carbonate aquifer in Kuwait is part of the most extensive limestone aquifer in the Arabian Gulf States. The principal artesian aquifer consists chiefly of 175-275 m thick, soft, porous chalky limestone and hard crystalline dolomitic limestone. The purpose of this paper is to describe the hydrochemistry of the groundwater and to identify the major geochemical processes operating within the carbonate aquifer during the last thirty years. A speciation model has been applied to the groundwater data to determine the chemical speciation during the studied period from 1972-2002 using the WATEQ4F program. Moreover, a mass-balance model has been applied for the period 1993-2002 to interpret the net geochemical reactions along the flow path. In addition, the W ATEV AL program was used to deduce the source-rock and to identify the major geochemical processes that influence the groundwater quality of the Dammam carbonate aquifer. This study reveals that the main water genetic types are: SO4-Na, Cl-Mg and Cl-Ca, which represent both continental and marine environments as an origin of the formation of groundwater. The water chemical types are dominantly Na2SO4, CaSO4 and NaCI. Speciation calculations indicate that the groundwater is typically oversaturated with respect to calcite, aragonite and quartz, and it is undersaturated with respect to anhydrite, gypsum, halite and dolomite. The calculated mean values of PCO2 range between 2.77 x 10-4 atm. and 8.72 x 10-3 atm. suggesting that the carbonate aquifer is a closed system with respect to CO2. The application of the mass-balance technique indicates that ion-exchange, reverse ion-exchange and dedolomitization are the prevailing geochemical processes in the aquifer. In addition, the ratio HCO3-/SiO2 10 suggests dominant carbonate weathering