Ukpokiti Field Reservoir Characterization: A Sequence Stratigraphic Approach to Field Appraisal

Wendy P. Houghton, Jeffrey W. Yeaton

In 1993 Conoco completed the Ukpokiti-1 well, Niger Delta. Gas and oil reservoirs were encountered in Late to Middle Miocene sands. A 3-D survey was shot as part of the appraisal of this discovery.

This poster will show how comprehensive biostratigraphic and 3-D amplitude and AVA data reinterpretation incorporating results of appraisal wells, provided a clearer reservoir model.

Evaluation of the wireline log and biostratigraphy from Ukpokiti-1 provided critical elements for developing a sequence-stratigraphic model for the area. The interpretation suggests that the Late Miocene section penetrated in Ukpokiti-1 has at least three sequences. Each is dominated by middle neritic to upper bathyal sediments. However, a similar analysis of Kunza-1, nearby, suggested a different depositional model.

The Ukpokiti reservoir lies within a subtle prograding complex. The reservoir appears to downlap a basal reflector. Mapping downlap terminations using surface horizon amplitude strength defined the direction of sediment transport and the potential limit of the reservoir. Amplitude and AVA anomalies are slightly offset from the crest of the structure and down dip of the structurally defined spill-point. Downlap terminations, amplitude anomaly patterns, and biostratigraphy suggest rapid reservoir variations across the structure.

Our understanding of the depositional environment and facies distribution was clarified through seismic and sequence stratigraphy in 3-D. Reservoir characterization is now more predictable in the Ukpokiti field.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995