Résumé
It is of interest to simulate the porosity changes associated with fluid flow and water–rock reactions in sedimentary systems. The chemical species taken into account are: {H
2O, H
+, Ca
++, HCO
3
−, Mg
++, Al(OH)
4
−, H
4SiO
4, K
+, Na
+, Cl
−}. The solution is assumed to be locally at equilibrium with different mineral assemblages including at least calcite, dolomite and one Mg–Al-silicate. These assemblages buffer the partial pressure of CO
2 (
Pco
2 ) which increases with temperature (
T) as is commonly observed in natural systems. The nature of the Mg–Al-silicate and the presence or absence of other at-equilibrium minerals (i.e. the feldspars) do not modify the
Pco
2–
T relationship. Considering complete transfer between the solution and the solid phases, computed relative porosity increases with increasing temperature for all the systems that were investigated. However, the direction and the amount of the clay transfer depend on the presence of feldspars. Furthermore, it is shown that computing mass transfer using a prescribed
Pco
2, as is commonly done, leads to very different values of mineral transfers. Hence, it must be concluded that prescribing a
Pco
2 value, even if the proper
Pco
2–
T relationship is used, leads to erroneous results.