Sedimentological and Diagenetic Characterization of Albian Carbonate Reservoirs - Example of Deep Water Marlim Leste Oil Field, Campos Basin, Brazil

Brito, Fernanda S.¹; Oliveira, Daniela L.²
(1) Exploration, Petrobras, Rio de Janeiro, Brazil. (2) Research Center, Petrobras, Rio de Janeiro, Brazil.

This paper aims to characterize the Lower and Medium Albian carbonate reservoirs of Macaé Group, Quissamã Formation, in the deep water field of Marlim Leste, Campos Basin, Brazil. The field produces from high-energy carbonate rocks, and is limited by a raft structure formed by halokinesis towards basin centre. Petrography, SEM, cathodoluminescence, XRD, stable isotopes and petrophysical analysis obtained from cores, side wall cores and cutting samples from several wells were used.

Analysis defined 13 main lithofacies, with prevalence of carbonate over siliciclastic rocks. Oolitic and oncolitic grainstones, deposited in high-energy banks and shoals, together with oolitic, oncolitic and bioclastic packstones deposited in moderate energy bars are the main producer facies. Other distinctive facies are: 1) peloidal packstones/wackestones deposited in protected areas with moderate to low energy; 2) bioclastic and peloidal wackestones/mudstones from low-energy lagoonal areas; 3) mudstones with planktonic foraminifera from external platform, low-energy and relatively deep water settings; 4) dolomites of evaporative origin near basal salt layers; and 5) hybrid siltite/arenite marking episodic siliciclastic entries.

The facies described are typical of a carbonate ramp and the Abu Dhabi recent deposit can be used as an analogue.

The definition of diagenetic paragenesis was used to discriminate which events are substantially important for porosity generation/enhancement. Diagenetic events that were observed in most Albian rocks are:

bioturbation/burrow, grain micritization, organic matter piritization, early isopachous cementation, dissolution, chemical compaction, dolomitization, spar calcite cementation, grain silicification and late dissolution.

The diagenesis shows different patterns from the base to the top of the reservoir. In the base, an intense two-phase dolomitization replaces matrix and cement, and dissolution of grains can be observed. Cementation by anhydrite is also present. In top part of Lower Albian, fractures are common, filled by at least four phases of spar calcite cementation. Exotic minerals such as barite, celestite, fluorite, and dickite/kaolinite were also observed and can be related to thermal fluids ascending through conduits.

The understanding of facies distribution, sedimentation conditions and diagenetic overprint will allow to better characterize reservoir quality throughout the field.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.