Origin of Breccia Fabrics in the Late Cretaceous Reservoir of the Cantarell Field, Offshore Campeche, Mexico

Horbury, Andrew¹, Richard Chambers², David Zamora³, Enrique Ortuno³, Ricardo Bello⁴ (1) Cambridge Carbonates Ltd, Solihull, West Midlands, United Kingdom (2) Quantitiative Geosciences, Broken Arrow, OK (3) Pemex Exploracion y Produccion, Mexico (4) Consultant, Mexico City, Mexico

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.