Reservoir biostratigraphy of the Pedernales Field, Venezuela

Abstract

Abstract The geographic and geological settings of the Pedernales Field, and its history from discovery to development, are briefly outlined. Biostratigraphy and palaeoenvironmental interpretation, and their impact on integrated reservoir description (IRD) and production geology, are discussed in detail. Historical and modern vintage micropalaeontological data enable the recognition of a number of ‘zones’ over the reservoir interval. These ‘zones’ are diachronous, although they do have correlative value when integrated into the framework of isochronous tectonostratigraphic sequence boundaries and flooding surfaces identified on seismic sections and well logs. The ‘zones’ and their containing sediments can be tentatively calibrated against global standard biozones and hence sequence boundaries and flooding surfaces on the eustatic sea-level cycle chart. Micropalaeontological and palynological data also enable the recognition of a number of biofacies interpreted on the basis of modern analogy as indicating a range of delta-top, delta-front and prodelta environments. The principal reservoir is interpreted as having been deposited in a range of delta-top to delta-front subenvironments, the seal in a range of distal prodelta subenvironments. The ongoing high-resolution biostratigraphic work programme has revealed the existence of a large number of correlatable events over the reservoir interval. Integrated high-resolution biostratigraphic, well log and seismic correlation can be achieved both within and between the compartments of the field. High-resolution biostratigraphic/biofacies data demonstrate the existence of a bathymetric gradient at the time the reservoir were being deposited. Gravity gliding along the observed gradient provides a possible mechanism for the locally observed section repetition and enhanced reservoir development, and also for the up-dip trapping mechanism.