The mechanisms of interaction between sandstone minerals, particularly clays, and two alkalis, NaOH and KOH, have been studied in order to better understand the response of sandstone reservoirs to alkaline treatments as a function of sandstone mineralogy and the nature of the alkaline solution. Such interactions are of primary importance in currently applied alkaline flooding and matrix stimulation processes.

The clay-alkali interaction can be described as an incongruent dissolution with the precipitation of new aluminosilicates. With NaOH. a crystalline zeolite precipitate appears at the tested temperatures (90, 150°C). With KOH, amorphous precipitates are present at these temperatures, followed by crystalline precipitates at 200°C

Response of Berea cores to NaOH and KOH treatments has been studied and is explained on the basis of the observed dissolution/precipitation mechanisms. Permeability changes and clay reactivity with fresh water are directly related to the amount of dissolved minerals and the extent of precipitation.

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