Origin of Breccia Fabrics in the Late Cretaceous Reservoir of the Cantarell Field, Offshore
Horbury, Andrew1, Richard Chambers2,
David
Zamora3, Enrique Ortuno3, Ricardo Bello4 (1)
Cambridge Carbonates Ltd, Solihull, West Midlands,
Previous models for the Cantarell
Field show Late Cretaceous breccias to be a result of normal slope processes (Viniegra-O., 1981) or due to catastrophic platform margin
collapse (Grajales, 2000). Our study focussed on a larger dataset (400 wells) than previous
authors and was aimed at developing a detailed log-based sequence stratigraphy calibrated by core data, with particular
emphasis on clast provenance. The aim of our study
was to construct a new static model in order to better simulate the field and
manage plateau production and field decline.
Our results show
that there is significant thickening towards the south of the field (up to
500m). The stratigraphy can be divided into four
units; a basal deepwater (planktonic foraminiferal marl) interval which has a high K,Th content; a middle unit which has a predictable,
cyclic stratigraphy of low-gamma carbonates which can
be correlated across the entire field and appears dominated by monomict breccias; an upper unit which has a U-dom-inated high-gamma signature and which consists of polmyict carbonate conglomerates; and a very uppermost
unit, which differs from the upper unit by the addition of exotic fragments of
volcanic glass. We analysed the net thickness of
low-gamma carbonates (defined by a GR cutoff of 12.5API or less) which shows a
belt of ‘clean’ carbonates running through the centre of the field from NW-SE.
The bulk of this low-gamma response is from the middle unit. Core control
indicates that to the SW side of the low-gamma belt, there are typical slope limestones, where clasts of rudist-rich limestone sit in a globotruncanid-rich
marly wackestone matrix.
The low-gamma belt is poorly constrained by core but data suggests that it is
largely dolomitised, with mimetic textures indicating
bioclastic/peloidal packstone
and grainstone.