Geochemistry of formation waters from upper Cretaceous calcareous rocks of southeast Turkey

Hydrochemical and isotopic study of groundwaters of Adiyaman region in Turkey is undertaken to classify groundwaters on the basis of their chemical characteristics, and examine their origin. The compositions of groundwaters in the calcareous rocks of the Adiyaman region reflect different combinations of fresh and saline groundwaters. The chemistry of the shallow groundwaters of Komur Municipality Spring (KS) and well of General Directorate of Adiyaman District (FG), and, especially of the major cations, is controlled by local rock compositions. While these are immature groundwaters geochemically, formation waters are generally mature groundwaters. Based on TDS classification, FG, KS and, Ataturk Dam Lake (ADL) samples are of fresh water (0-1000 ppm), Adiyaman (A44) and Cemberlitas (C14) formation water samples are of brackish water (1000-10000 ppm), and other formation waters are of connate water (10000-30000 ppm). Adiyaman formation waters (A32 and A44) have a sequence of rCl>rHCO(3)>rSO(4) and are undersaturated with respect to CaSO4. Formation waters of other oil fields have a sequence of rCl>rSO(4)>rHCO(3) and are oversaturated with respect to CaSO4. Conservative ions in formation waters, such as Cl and Br, were used together with total dissolved solids in determining the evolution of waters and in the evaluation of mixing. In this respect, there is a transition between fresh and connate waters. It is concluded that Adiyaman and Cemberlitas formation waters show greater mixing with fresh groundwaters than other formation waters of the Adiyaman region.