The relationships between sedimentological facies and diagenetic properties differ depending on burial and geological history. In this paper we propose several examples where different quantitative expressions of diagenetic imprints lead to different workflows to be applied, to obtain final simulations reproducing both the sedimentary facies and the diagenetic trends in reservoir models.
A first case is based on an outcrop study of mixed siliciclastic-carbonate facies. The relationships between sedimentary facies and diagenesis have been used to define truncation rules for the plurigaussian algorithm, which aims at simulating both the distribution of sedimentary facies and the diagenetic overprint. Another workflow has been developed on this example, using the bi-plurigaussian simulation algorithm to address the problem of heterotopic bivariate conditional simulation (the two variables are known at different locations).
A second example is related to early diagenesis characterization. In this example (Madison Formation, Wyoming, USA), diagenetic imprints have been quantified, corresponding to a succession of diagenetic phases (micritization, calcite cementation, dolomitization...), that can coexist in the same sedimentary facies. The workflow using plurigaussian and nested simulation algorithms shows the impact of such joint simulations, as the diagenesis may completely modify the distribution of reservoir properties only based on a facies simulation.
In a third example, the modeled Aptian/Albian formation includes hydrothermal dolomites (HDT) associated to fractures and faults hosted in reefal and slope limestones. Simulations succeed in redistributing the HTD correctly at the surface and in the subsurface. Hence, in the deeper parts of the Aptian/Albian reefal rock unit, the dolomite is inherently associated to fractures, while at shallower levels, dolomitization seems to be more lateral, affecting probably more permeable facies. These results provide insights and numerical means for estimating volumes of dolomites (vertically and laterally) in an excellent case study of fracture-related HTD.
Diagenesis alters the original relationships between depositional facies and petrophysical properties in a reservoir. The quantitative integration of sedimentological facies and diagenetic properties is a key point to obtain a realistic geological model in reservoir studies.