POROSITY ENHANCEMENT DURING CLASTIC DIAGENESIS AS A RESULT OF AQUEOUSMETAL-CARBOXYLATE COMPLEXATION - EXPERIMENTAL STUDIES

This paper reviews the results of experiments that place constraints o n the role of aqueous metal-carboxylate complexes during clastic diage nesis. Two types of experimental studies are reviewed: (1) feldspar so lubility experiments; and (2) experiments on limited-component systems designed to determine the stoichiometry and thermodynamic stability o f aqueous metal-carboxylate complexes. Although there are many apparen t inconsistencies between the studies, all of the experimental evidenc e is consistent with the occurrence of aqueous complexation between na turally-occurring difunctional carboxylic acid anions and Al in neutra l to slightly acidic subsurface fluids. Furthermore, this complexation could cause significant transport of Al during clastic diagenesis. Mo st experimental studies indicate that complexation between Al and mono functional anions is of limited importance to Al transport. Additional ly, there is no definitive experimental evidence that complexation bet ween Si and mono- or di-functional carboxylic acid anions occurs in na tural systems. Thermodynamic modelling indicates that the solubility o f calcium-oxalate salt limits, but does not negate, the importance of aluminum-oxalate complexation. Specifically, a pH-4 fluid in equilibri um with gibbsite at 80-degrees-C with 500 ppm oxalate and 250 ppm Ca w ould be undersaturated with respect to solid calcium-oxalate and would be able to maintain 50 ppm Al in solution as an aqueous aluminum-oxal ate complex.