1887
Volume 31, Issue 4
  • ISSN: 1354-0793
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Abstract

Sahabi ‘B’ Reef is one of several pinnacle reefs located in the southern part of the Ajdabiya Trough. The Sahabi ‘B’ Reef is ambiguous for several reasons: only four wells have penetrated the reef, resulting in limited subsurface information; two wells were abandoned as dry wells, while the other two have produced from different oil pay zones, indicating strong lateral facies variation in and around the reef. Utilizing seismic and well data, the distinct depositional architecture of the carbonate Late Paleocene successions and their potential as petroleum reservoirs are examined. The study aims to explain why some wells in the Sahabi ‘B’ Reef complex are producing while others are not, and to identify facies changes that facilitate an understanding of their evolution over geological time. Four developments of the lithofacies in the Upper Sabil Carbonate have been differentiated from bottom to top: (1) open shallow-marine packstone/grainstone; (2) bioclastic grainstone/packstone with tidal effect; (3) coral floatstone/boundstone; and (4) bio-lithoclastic talus. The Sahabi ‘B’ Reef consists of two reefs (older and younger parts). During the Middle Eocene, the area generally dipped towards the location of the younger reef. A tilt is attributed to bending rather than faulting, causing minor saddles and humps between these two reefs. This could plausibly explain the presence of oil accumulation in the younger part of the Sahabi ‘B’ Reef, while its absence is noted in the older part. The reef complex is seismically divided into major lateral facies, which vary in terms of deposition and age; these include: (1) older reef, (2) shoal, (3) younger reef and (4) talus. During the Paleocene, Upper Sabil carbonates exhibited an aggrading build-up that kept pace with relative sea-level rise, marking the first Sahabi ‘B’ Reef formation. Subsidence and relative sea-level rise resulted in the backstepping of the second Sahabi ‘B’ Reef within the pre-existing topography. By the end of the Paleocene, this stage marks the conclusion of the Sahabi ‘B’ Reef complex, when the reef was drowned due to rapid sea-level rise, leading to a basin dominated by shale deposition.

© 2025 The Author(s). Published by The Geological Society of London for GSL and EAGE. All rights, including for text and data mining (TDM), artificial intelligence (AI) training, and similar technologies, are reserved. For permissions: https://www.lyellcollection.org/publishing-hub/permissions-policy. Publishing disclaimer: https://www.lyellcollection.org/publishing-hub/publishing-ethics

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2025-11-20
2026-01-24

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The Sahabi ‘B’ Reef complex in the Sirt Basin, Libya: insights into the geometry and depositional architecture of a reservoir
Petroleum Geoscience 31, petgeo2025-019 (2025); https://doi.org/10.1144/petgeo2025-019
/content/journals/10.1144/petgeo2025-019
/content/journals/10.1144/petgeo2025-019
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