Skip to Main Content
Book Chapter

Pre-salt microbialites from the Campos Basin (offshore Brazil): image log facies, facies model and cyclicity in lacustrine carbonates

By
M. C. Muniz
M. C. Muniz
1
Petrobras, Avenida República do Chile, 330 – 10th Floor, 20031-170 Rio de Janeiro, Brazil
Search for other works by this author on:
D. W. J. Bosence
D. W. J. Bosence
2
Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
Search for other works by this author on:
Published:
January 01, 2015

Abstract

This study uses a borehole image log, supported by limited sidewall-core samples, and conventional wireline logs to erect facies and stratigraphic models for the Aptian pre-salt microbial carbonates (Macabu Formation (Fm)) of the southern Campos Basin, Brazil. This supports the widely held view that these reservoirs are very significant, unusual, partly microbial, and lacustrine in origin. This single-well study penetrates 220 m of microbialite facies from the pre-salt Lagoa Feia Group non-marine carbonates. Continuous borehole images, available sidewall-core data, and gamma-ray and sonic wireline logs are used to identify and characterize borehole image facies. These facies are interpreted to have formed in four lacustrine depositional environments: deep subaqueous, intermediate subaqueous, shallow subaqueous and subaerial. The borehole image facies commonly show shallowing-upward facies trends topped by emergent surfaces. Such trends are interpreted as metre-scale, high-frequency cycles that are grouped into lower order depositional sequences interpreted from the gamma-ray log. A Fischer plot of the high-frequency cycle suggests that the entire Macabu Fm is represented by a decrease in the accommodation space followed by increase in the accommodation space; consistent with this suggestion are trends in δ18O values from an adjacent well that indicate an initial trend of increased evaporation followed by increased freshwater inflow (lighter δ18O and thicker cycles).

You do not currently have access to this article.

Figures & Tables

Contents

Geological Society, London, Special Publications

Microbial Carbonates in Space and Time: Implications for Global Exploration and Production

D. W. J. Bosence
D. W. J. Bosence
Royal Holloway, University of London, UK
Search for other works by this author on:
K. A. Gibbons
K. A. Gibbons
Nexen Petroleum UK Ltd, UK
Search for other works by this author on:
D. P. Le Heron
D. P. Le Heron
Royal Holloway, University of London, UK
Search for other works by this author on:
W. A. Morgan
W. A. Morgan
Morgan Geoscience Consulting, LLC, USA
Search for other works by this author on:
T. Pritchard
T. Pritchard
BG Group, UK
Search for other works by this author on:
B. A. Vining
B. A. Vining
Royal Holloway, University of London, UK
Search for other works by this author on:
Geological Society of London
Volume
418
ISBN electronic:
9781862397163
Publication date:
January 01, 2015

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal