Influence of dolomitization process on the geochemistry of the carbonate and clastic aquifers induced by vertical flow , Kuwait

The Umm Gudair well field in Kuwait supplies brackish groundwater at a peak rate of 1.14 x 105 m3/d from 41 dual completed production wells. Each well can be operated continuously at a capacity of 2,620 to 3,110 m3/d. The produced water is expected to be a mixture of the pumped Kuwait Group and Dammam Limestone aquifers. Thus, the quality of the pumped water is affected by this production method, since the two aquifers are different in their chemical and physical properties. This paper discusses the impact of the groundwater exploitation methods on the hydrogeochemistry of carbonate and clastic aquifers, when they are treated as a single reservoir. Dedolomitization, which increases sulfate and carbonate complexes in the solution, is the major geochemical process controlling the water chemistry of the Kuwait Group aquifer. Incongruent dissolution of dolomite is the major geochemical process controlling the groundwater chemistry of the Dammam Limestone aquifer. The mClI mNa ratio in the Kuwait Group aquifer indicates that Na + ions are removed from solution by a reverse ion exchange process. However, the mCdmNa ratio in the Na-SO4 water type of the Dammam Limestone aquifer indicates the occurrence of a natural softening process. The exploitation method in the Umm Gudair well field causes a vertical flow from the upper clastic Kuwait Group aquifer to the lower carbonate Dammam Limestone aquifer, which disturbs the original geochemical processes in these aquifers. The resulting water chemistry indicates that the dolomitization process is likely to be the major controlling factor in both aquifers due to mixing of water from both aquifers by vertical flow in the Dammam Limestone aquifer. The exploitation method affects the suitability of the pumped water for irrigation purposes, by increasing the SAR ratio and boron concentration, and by changing the saturation index of gypsum in the solution