Postdepositional Evolution of the Carbonate Reservoir Systems from the Moesian Platform (Romania)

Nicolae Anastasiu and Dumitru-Relu Roban
University of Bucharest, Bucharest, Romania

A sedimentological analysis has been performed in order to point out the postdepositional (diagenetic) evolution of the reservoir architectures component of some Moesian Platform structures. Several methods - grain- size & shape analyses, microstructures examination, cathodoluminiscence and U.V. fluorescence studies - have been applied.

Specific postdepositional processes acted differently - spatially and temporally - and have been identified, as follows: differential compaction and illuviation of matrix, sindepositional bioturbations, micritizations, vadose- and submarine cementations, polymorphic transformations, recrystallizations (by aggradation), authigeneses of calcite, dolomite and pyrite, pressure solutions, and joints/ fractures.

Recrystallizations are the most frequently, selective, and affect the matrix, peloides, intraclasts and bioclasts . The process is never complete, not symmetrical. Microstylolites are effect of pressure solution, and cover the boundaries between the litons. Dolomitization it was a recurrent processes, in telogenesis, and mesogenesis stages.

The effective and total porosity of the studied reservoirs is directly subject to this processes, that specifically controlled modifications of "grain- support" and pore space as well, within three diagenetic stages: incipient burial (eogenesis), uplifting (telogenesis) and, respectively, progressive burial (mesogenesis).

The hydrocarbons dynamic - either from source to reservoir bodies or inside reservoirs - could be considered as a complex process, mainly controlled by pore space configuration and by the relationship between the time of hydrocarbon maturation and the evolution of each process modifying pore space.

The prediction of hydrocarbons in dolomitic reservoirs - which hosted a large void, should be connected with depositional model.

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