Abstract: Deep Water Sequence Architecture and the DUO Attribute Display; Characterizing Fans from Seismic Data in Central Offshore Nigeria and Gulf of Mexico
Radovich, Barbara J. - Texaco E&P; R. Burnet
Oliveros, David
L. Connolly, Daniel B. Denson, and Sally D. Zellers - Texaco
Deep water wells that are likely to exceed economic thresholds must penetrate fans with the greatest thickness and lateral continuity. Combining instantaneous attribute analysis with an understanding of sequence stratigraphic architectures from passive margin settings can improve predrill predictions and post-drill assessment of these factors. In addition, pseudocolor combination displays from satellite image techniques can be easily adapted to the display of instantaneous seismic attributes, with each attribute treated as a different coincident channel of information.
Seismic sequence interpretation in the deep water central Offshore Nigeria and Gulf of Mexico shows a vertical series of sequences dominated by a predictable succession of lowstand fan types and depositional processes (Fig. 1). This sequence stratigraphic architecture is important to recognize because sequence stratigraphy gives clear strategies and criteria for how to interpret horizons on the workstation and what the intervals mean for further geophysical analysis. As the margin progrades through time, the fan facies also shift basinwards forming a succession of sequences called here the ?Fill Profile? of the margin. Using simplified criteria, fan plays can readily be interpreted on the seismic data and compared to key wells. The seismic section is divided into four zones of sequences, each with a dominant fan type. The oldest zone is comprised of sequences dominated by basin floor fans that have come to rest on the basin floor during the greatest fall of sea level. These have potential for the greatest lateral continuity but characteristically show the fewest ?fan? features on the seismic data. The next youngest zone is comprised mainly of distal slope fans that represent the terminal lobes at the end of channelized delivery systems. These may have acceptable lateral continuity, and aggrade to form low mounds and channel/lobe shapes. The proximal slope fan zone is characterized by confined, sinuous channel sands and levee overbanks and thus often has problems with reaching economic thresholds in deeper water areas. The shallowest zone is comprised of sequences with highly discontinuous sands deposited in cut and fill features of an active (slump and erosion) slope.
The application of the DUO attribute calculation, a combined response amplitude and frequency display, within this sequence stratigraphic framework can give insight into several fan interpretation problems (Fig. 2). These displays give quantitative support to seismic sequence interpretation of fan types, aid in discerning seismic amplitudes of sand-prone fans from those of condensed sections, and can help find subtle sequence boundaries. The ?Discontinuity? attribute has received attention primarily for fault identification but can lend quantitative support to interpreted sequence and facies boundaries.
AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil