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

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/diffusional-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 t he sandstones, and the quantity of silica transport into and out of the san dstone by advecting fluids is negligible. Integration of the coupled mass t ransfer/transport equations over geologically relevant time frames is perfo rmed using the quasi-stationary state approximation. Results of calculation s performed using quartz dissolution rate constants and aqueous diffusion c oefficients generated from laboratory data, are in close agreement with bot h the overall porosity and the distribution of quartz cement in the Middle Jurassic Garn Formation only after optimizing the product of the effective surface area and quartz precipitation rate constants with the field data. W hen quartz precipitation rate constants are fixed to equal corresponding di ssolution rate constants, the effective surface area required to match fiel d data depends on the choice of laboratory generated quartz rare constant a lgorithm and ranges from 0.008 cm(-1) to 0.34 cm(-1). Tn either case, these reactive surface areas are similar to 2 to 4 orders of magnitude lower tha n that computed using geometric models. (C) 1999 Elsevier Science Ltd. All rights reserved.