| Abstract: | The evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable; this evolution can be typified by five generalizations (1) at or near 80°C there appears to be an exponential rise in the concentration of organic acid anions; (2) the maximum concentration of organic acid anions occurs over approximately the 80–100°C temperature interval; (3) the highest concentrations of difunctional acid anions are associated with the other organic species maxima; (4) difunctional acid anions are the first to be decarboxylated, typically at temperatures of 100–110°C; (5) with increasing temperature (110–130°C) monofunctional acid anions begin to become decarboxylated, resulting in a fluid alkalinity dominated by bicarbonate. Dissolution experiments using artificial and natural oilfield waters demonstrate that mono- and difunctional carboxylic acid anions and hydroxybenzoic acid anions (present in both oilfield waters and the aqueous phase of hydrous pyrolysates) are capable of greatly enhancing Al, Si, Fe and Ca concentrations in solutions from dissolution of minerals by organometallic complexation. This enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs; certainly, no other viable mechanism has been proposed to explain aluminum transport in the subsurface. When integrated into basin models, the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems. |
