AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Carbonate Reservoir Characterisation: A Middle East Case Study Using 3-D Seismic Analysis Workflows
(1) ffA, Aberdeen, United Kingdom.
(2) Dubai Petroleum Establishment, Dubai, United Arab Emirates.
Poststack seismic analysis techniques are very effective at highlighting subtle features in carbonate zones when conventional techniques give ambiguous or inconclusive results. In this study, we used seismic analysis workflows to address two problems encountered in neighbouring fields in the Persian Gulf, one structural and one stratigraphic.
The data used in this study were dominated by steeply dipping coherent noise. This not only made interpretation difficult but also introduced artefacts into the subsequent processing. Structurally oriented noise attenuation was therefore an essential first step in the processing workflow.
The stratigraphic challenges occur in the Middle Cretaceous Mishrif reef build-ups. These carbonate build-ups were controlled by localised salt diapirism and associated bathymetric variations. Directly below the Mishrif horizon, clinoforms and pinch-outs are known to exist but are difficult to identify on the seismic data. The Bedform workflow was used to identify individual events, and when combined with instantaneous frequency was used to extract the pinch-outs as 3D geobodies.
The structural issues occur in the massive aggrading Thamama complex of Lower Cretaceous age, where there are two potential fault scenarios. The objective of the structural workflow was to identify the subtle faulting around a key well location to clarify which of the faulting scenarios was present. A combination of structurally oriented attributes identifying both discontinuities and curvature were used to highlight the faults and confirm one of the scenarios.
A good understanding of the geomorphological evolution, as well as the structural and stratigraphic properties of these formations is crucial in defining reservoir properties. Attribute analysis and object extraction has proved to be a valuable tool for detailed investigation into the carbonate features within these UAE fields. It has provided a level of detail that is hard to achieve with manual interpretation and has given new insights into the geology and reservoir properties of both fields.