THE EFFECT OF HYDROTHERMAL REACTIONS ON THE PETROPHYSICAL PROPERTIES OF CARBONATE ROCKS

Samples of carbonate rocks, both limestones and dolomites, were subjected to static hydrothermal tests to determine the extent to which mineral reactions affect petrophysical properties. Most samples showed evidence of the reaction of kaolinite and dolomite to produce smectite. Because the amount of clay minerals in these rocks is very limited, the reaction products are not abundant, constituting less than one percent of the rock mass. The small amount of smectite produced is sufficient, in some of the experiments, to cause marked changes in the pore-size distribution of the rocks, resulting in very different mercury recovery efficiencies before and after hydrothermal testing. A simple calculation shows that the amounts of smectite produced are adequate to account for the rather drastic changes in efficiency of mercury recovery.