Interpreting Static and Dynamic Connectivity Across Potential Structural and Stratigraphic Boundaries: A Case Study in a Mature Oil Field

Larry T. Sumpter¹, Ellen Meurer¹, Devlin Bill², and Kenneth Petersen^1
1ExxonMobil Upstream Research Company, Houston, TX
²ExxonMobil Production Company, Houston, TX

The field studied is located offshore Nigeria and produces oil from bedded and "disturbed" (rotated to chaotic slump strata) fluvial-deltaic sands. The field includes more than sixty wells exploiting ten stratigraphic intervals on six structures. Truncation of the bedded by the disturbed across an angular unconformity produces a potential stratigraphic connection between most of the producing reservoirs. The objective of this study was to build a geologic framework describing the original continuity of the oil and gas columns across potential structural and stratigraphic boundaries (static connectivity), then use this framework to understand fluid movement during production (dynamic connectivity) and identify bypassed oil. Lacking pre-production pressure data, original fluid continuity across the field was interpreted from logged fluid contact elevations, mapped structural and stratigraphic relationships and geochemical data. From this part of the study we conclude that fault juxtaposition connections and the stratigraphic connectivity provided by the angular relationship between the disturbed strata and underlying bedded horizons are sufficient to explain common original fluid contacts shared laterally across potential structural boundaries and vertically across marine shales and shaley siltstones. This static framework was then compared to post-production pressure data, logged contact data, production characteristics and cumulative production volumes for each stratigraphic interval on each structure. Here we conclude that truncation and fault juxtaposition connections are effective on a production time scale and result in fairly uniform pressure drawdown throughout the field, while the marine shales/siltstones are adequately continuous with sufficiently low permeability to prevent direct vertical movement of oil from one producing interval to another.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas