The Role of Organic Acids in Feldspar and Quartz Dissolution at 100 degree C/347 Bars: An Experimental Study

Abstract

Water-soluble organic anions are capable of dissolving feldspar and quartz under diagenetic conditions and maintaining high levels of Al and Si in solution. It has been shown that abundant organic acids are released prior to and possibly during hydrocarbon generation. The combination of dissolution and complexing capacity suggests that organic acids may be of significant importance in mineral dissolution and secondary porosity development in sandstones in the diagenetic environment. Dissolution of albite and quartz was studied using flow-through hydrothermal vessels at 100C and 347 bars. Buffered 5,000 ppm acetate/500 ppm oxalate solutions (pH = 4.7) were passed through sand packs of 250-500 {mu}m Amelia albite (Ab{sub 97-99}) and Brazilian hydrothermal quartz. The solid starting material was cleaned ultrasonically to remove any adhering ultrafine particles. Organic species were analyzed using ion chromatography. Steady-state concentrations of SiO{sub 2} and Al average 237 ppm and 50 ppm, respectively. These values are significantly higher than predicted by the solubilities of common aluminosilicate clay minerals in water. This suggests that the amount of Al held in solution by complexing is very high, significantly reducing the amount of Al available for clay precipitation. The lack of authigenic aluminosilicates indicates the efficiency of the organics in removingmore » and transporting Al and Si. Future work with aliphatic and aromatic organics, as well as inorganic acids, will allow comparison of the role of various aqueous species in mineral dissolution and secondary porosity development.« less