Making diagenesis obey thermodynamics and kinetics: the case of quartz cementation in sandstones from offshore mid-Norway (original) (raw)

Calculation of the quantity and distribution of quartz cement as a function of time and temperature/depth in quartzose sandstones is performed using a coupled dissolution/diusional±transport/precipitation model. This model is based on the assumptions that the source of the silica cement is quartz surfaces adjoining mica and/or clay grains at stylolite interfaces within the sandstones, and the quantity of silica transport into and out of the sandstone by advecting¯uids is negligible. Integration of the coupled mass transfer/transport equations over geologically relevant time frames is performed using the quasi-stationary state approximation. Results of calculations performed using quartz dissolution rate constants and aqueous diusion coecients generated from laboratory data, are in close agreement with both the overall porosity and the distribution of quartz cement in the Middle Jurassic Garn Formation only after optimizing the product of the eective surface area and quartz precipitation rate constants with the ®eld data. When quartz precipitation rate constants are ®xed to equal corresponding dissolution rate constants, the eective surface area required to match ®eld data depends on the choice of laboratory generated quartz rate constant algorithm and ranges from 0.008 cm À1 to 0.34 cm À1. In either case, these reactive surface areas are H2 to 4 orders of magnitude lower than that computed using geometric models.