The unique mechanism of analcime dissolution by hydrogen ion attack

Acidization is the process of injecting acid into porous oil bearing formations to dissolve minerals in the pore space and is a common technique to increase oil production. Analcime is a zeolite which is one of the minerals found in oil reservoirs in the Gulf of Mexico. This mineral is particularly troublesome during the injection of hydrochloric acid during stimulation of the well reservoir because of the precipitation of silicate and analcime dissolution products. To better understand the dissolution/precipitation process, a fundamental investigation of dissolution of analcime was carried out. Experiments establish that silicate precipitates completely from solution during analcime dissolution in hydrochloric acid and that the precipitation does not influence the dissolution kinetics. Comparison of Si and Al initial dissolution rates demonstrates that Al is selectively removed from the zeolite. The selective removal rate parameter is defined as the ratio of the measured Si dissolution rate to the stoichiometric Si dissolution rate. A new concept is introduced of using the selective removal rate parameter to delineate the mechanism of particle dissolution by demonstrating the influence of the Si-to-Al ratio. The mechanism comprises the removal of Si facilitated by the selective removal of Al, leading to the formation of undissolvable silicate particles. Consequently, the unique mechanism of analcime dissolution has general implications pertaining to how microporous materials dissolve.