AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Depositional Processes and Correlation of Structurally Confined Deepwater Sandstones from the Upper Jurassic Buzzard Field, UKCS
(1) Department of Geology & petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom.
The upper Jurassic Buzzard field, UKCS, is a structurally confined deepwater sheet turbidite system with updip stratigraphic pinchout to the west and limited by extensional faults to the north and south. A wealth of subsurface information is available including over fifty wells with full log suites and image logs, over 3,000ft of core through the reservoir interval, chemo- and bio-stratigraphy, and a 3D seismic survey. Despite this, the sedimentology and depositional history of the system is not yet completely understood and stratigraphic correlation of lithofacies units is difficult.
Buzzard comprises sandstone units of up 60ft thickness interbedded with in-situ and remobilised mudstones along with cemented and injected sandstones. Sandstone units can be correlated basin wide whilst maintaining their thickness and with very little evidence of amalgamation surfaces. Thick Buzzard sandstone units are interpreted as single depositional events of non-erosive high-density, accumulative turbidity currents confined only by the basin margins triggered by catastrophic mass failure events. Fine material, which was not in high concentration in the initial flow, has been transported beyond the Buzzard basin and deposited in a more distal location.
Mass transport deposits, particularly slump deposits are observed in core and are concentrated towards basin margins. The interaction of turbulent flow with mass transport deposits is used to explain any variation or lateral discontinuity of Buzzard sandstones. Slump deposits are difficult to identify in core, in wireline logs and in seismic data as they often contain large coherent blocks. Therefore, lithofacies identification is vital for accurate stratigraphic correlation. Curves derived from dipmeter data can be used in conjunction with conventional log curves to improve the recognition of lithofacies. Identification of remobilised lithological units provides context for chemostrigraphic and biostratigraphic analysis and allows a comprehensive chronostratigraphic framework to be constructed.
A multi-disciplinary approach to stratigraphic correlation is essential to understand the Buzzard depositional system. Dipmeter data can aid lithofacies identification and improve lithofacies correlation. Understanding the system and the interplay between successive sediment gravity flow deposits will aid production from the field and ultimately lead to an increase in recoverable reserves from the Buzzard field.