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Reaction Transport Modelling: Simulation of Reflux and Convection Dolomitization Models in from Isolated Carbonate Platform

Ronchi, Paola 1; Borromeo, Ornella 1; Consonni, A. 1; Battistelli, A. 2; Geloni, C. 2
1 Eni E&P Division, Eni SpA, San Donato Milanese, Italy.
2 Snamprogetti, S.p.A., Fano, Italy.

The dolomitization in a carbonate platform can occur at different times and in different diagenetic environments from synsedimentary to deep burial settings (Machel, 2004). A well constrained diagenetic interpretation allows assumptions to be made about the distribution of the dolomitized bodies (Whitaker, 2004). This is particularly important in the oil industry because the dolomitized bodies frequently have the best petrophysical properties, particularly ion the Paleozoic sequences (Lucia, 2004).

The results of diagenetic analyses do not always point to an unequivocal conceptual model. In this situation a numerical modelling exercise may help to select the model that best honours the mass balance, kinetic and thermodynamic constrains. Moreover, the effects of the diagenetic processes on reservoir properties may be estimated.

Several dolomite types are described from petrographic analysis, the most frequent type is finally crystalline, partly mimic, replacive (Fig. 2): the stable isotope signature (Carbon and Oxygen) and the petrographic relationship with burial stylolites support an origin in

The subject of this study is an application of the software of reactive transport modelling ‘Toughreact’: two dolomitization models have been tested, in order to strengthen the conceptual interpretation and to evaluate the main constraints on the dolomitization processes. The code calculates rock/water system evolution through the simulation of brine flux in a porous media, transport of chemical species in water solution and mineral/fluid reactions.

The study describes the simulation of dolomitization model change in an isolated carbonate platform from thermal convection to reflux model due to an increase of salinity and platform architecture modification. The simulated bank architecture consists of biohermal complex, Visean to Early Serpukhovian in age, capped by shallow bank interior deposits, Late Serpukhovian in age, that grade laterally to bank margin bioherms. Within the bank, time transgressive bodies of porous dolomite occur, that in general are located at the bank margins, but may also follow syndepositional fractured zones the shallow burial diagenetic setting, from circulation of marine water.

 

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009