Integration of diagenesis in basin-scale, stratigraphic forward models using reactive transport modeling: Input and scaling issues

Abstract

This article presents an integrated approach based on stratigraphic forward modeling and reactive transport modeling to adequately represent the development of a mixed siliciclastic-carbonate sedimentary system and its diagenesis. This work was realized on a realistic case study, the Oligo-Miocene series of Carry-le-Rouet, South-East of France, characterized by a complex pattern of bioclastic, bioconstructed and siliciclastic deposits, and affected by several exposure surfaces and associated meteoric diagenesis. A first phase consisted in building a stratigraphic forward model (SFM), using the software DionisosFlow. The construction of the model was based on sensitivity tests on the two main parameters controlling basin sedimentation: 1) competition between carbonate production and siliciclastic supply; 2) subsidence. The results of the simulations, especially the facies distribution, the thickness of the deposits and the sedimentary architectures were compared with the observed data to validate the model. A second phase consisted in focusing on a specific stratigraphic event and performing reactive transport modeling (RTM) on a 2D section extracted from the DionisosFlow model to evaluate the mineralogical transformations and resulting petrophysical evolutions created by early diagenesis. The calculation results show the occurrence of two domains of salinity, that were associated with two distinct diagenetic environments: marine and meteoric phreatic. Globally, the simulated diagenetic trends are qualitatively consistent with the petrographic observations, except for the replacement of aragonite by a calcite cement, that systematically occurred in the model and is not always observed in thin sections. This preliminary study emphasizes the issues associated with the application of RTM to diagenetic phenomena, linked with the uncertainties inherent to specific parameters, such as minerals kinetic properties, and the mismatch between the space and time scales of the modeled processes and the upscaled description of each SFM cell. These results argue in favor of an alternative solution, that could conciliate the different processes. The combination of the various SFM output properties with simplified chemical reactions whose rates have been tuned for specific diagenetic processes of interest could provide diagenetic risk maps that would constitute useful guides for exploration at basin scale.