Tectonics and carbonate platform development, Gabes-Tripoli Basin, offshore Libya
Final Report Abstract
The Gabes-Tripoli Basin of western offshore Libya encompasses and neighbours several large hydrocarbon fields (e.g. the Bouri Field with 1000–3000 Million barrels oil), which are of major economic importance for Libya. Despite the relevance and value of the basin, there are today several unsolved geological questions concerning the basin’s late Cretaceous to recent tectonic development; the role of a potential Triassic salt substratum influencing the development of hydrocarbon-bearing anticlines; and the interaction of tectonics and sedimentation controlling reservoir-rock deposition, reservoir fracturing, hydrocarbon migration and accumulation. This research project focused on a detailed structural-stratigraphic interpretation of the Gabes-Tripoli Basin based on 3D-seismic-reflection data and borehole information. A workflow was developed that specifically enhanced the seismic interpretability of faults and subsurface sedimentary systems (e.g. carbonate build-ups). The workflow integrates 3D-seismic data pre-conditioning, volume-attribute analysis and isochore (TWT) interpretation. Detailed 3D subsurface attribute interpretations show that (i) different groups of faults with different structural orientation characterise the different stratigraphic intervals between the Late Cretaceous and today; (ii) major anticlines associated with the main hydrocarbon reservoirs trend WSW-ENE and SSE-NNW, which is oblique to the dominant NW-SE fault trend. The SSE-NNW-oriented anticlines present a newly documented fold orientation in the basin; (iii) large N-S oriented, gravity-driven, synsedimentary listric normal faults formed at the edges of major anticlines bounding kilometre-scale sedimentary depocentres; and (iv) Paleogene anticline growth and growth faulting at the anticline edges was decoupled from the dominant Late Cretaceous to recent NW- SE-oriented, deep-rooted crustal fault trend. Combined tectonic and stratigraphic interpretation enabled the documentation of partial decoupling of Eocene to Oligocene overburden faulting in the western and central parts of the study area from otherwise basement-rooted strike-slip tectonics. Lateral and vertical subsurface evaporite movement in the Paleogene must be regarded as an important control for anticline growth and reservoir development in anticline crests, with contemporaneous and subsequent basement-involved strike-slip faulting contributing to a high variability in fault- and fracture-trends and types.
Publications
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Seismic Characterisation of Carbonate Systems and Reservoirs in Western Offshore Libya. Abstract volume: Seismic Characterisation of Carbonate Platforms and Reservoirs, The Geological Society, Burlington House, London.
Khalifa, N. & Back, S.
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Tectonic and Carbonate-System Development in Western Offshore Libya. Abstract volume: GeoBonn 2018, Bonn.
Khalifa, N. & Back, S.
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Deformation Patterns in Western Offshore Libya: Partial Decoupling of Strike-Slip and Salt Tectonics. 82nd EAGE Annual Conference & Exhibition, 1-5. European Association of Geoscientists & Engineers.
Khalifa, N. & Back, S.
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Folding and faulting offshore Libya: Partly decoupled tectonics above evaporites. Marine and Petroleum Geology, 124, 104840.
Khalifa, Nabil & Back, Stefan
