Tectonics and carbonate platform development, Gabes-Tripoli Basin, offshore Libya

Khalifa, Nabil; Back, Stefan (Thesis advisor); Kukla, Peter (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The research presented in this thesis targets the Cenozoic structural development of the Gabes-Tripoli Basin, the Cenozoic development of carbonate platforms, the interaction between tectonics and sedimentation fundamentally based on 3D seismic-reflection analysis integrated with borehole data in the Mediterranean Sea offshore western Libya. The study area (block NC41) encompasses numerous large hydrocarbon fields that are of major economic importance for Libya. Despite this clear relevance, there are still several unsolved geological issues that include: i) the interpretation of the drivers of the late Cretaceous to recent regional tectonic development of the Gabes-Tripoli Basin; ii) the influence of tectonics on sedimentary patterns and the basin-wide stratigraphy of the Gabes-Tripoli Basin; iii) the architecture and structural development of hydrocarbon-bearing anticlines offshore western Libya; vi) the role of a potential Triassic salt substratum for structural development, stratigraphy and hydrocarbon system development. The database used for research consists of three merged 3D seismic-reflection volumes covering an area of approximately 1200 km2 with 12.5 × 12.5 m binning. from 8 industrial wells in area C. And the area E is covered by different seismic volume covering an area of 800 km2 and borehole geophysical data from 8 industrial wells. All data was generously provided by the National Oil Corporation of Libya (NOC). The comprehensive subsurface dataset enabled regional overview interpretations of 3D seismic reflections between the acoustic basement (incl. salt?) of inferred Triassic age and the Cretaceous-to-recent sedimentary overburden. The database facilitates the detection and interpretation of both sedimentary and tectonic subsurface features in spatial details to a resolution of a few meters. The detailed, regional 3D seismic interpretation results were be ground-truthed at 13 well locations across the study area. Seismic interpretation began with a filter-based, post-processing seismic conditioning workflow that improved the signal-to-noise ratio by low-pass frequency filtering removing high-frequency noise. Random noise was then reduced by structure-oriented filtering - a low-pass filter implemented as a running-window average filter with edge-preservation. The use of the enhanced 3D seismic-reflection data increased the accuracy of subsequent reflection interpretation and improved the quality of seismic attribute generation, visualization and analysis. 3D seismic-attribute interpretation greatly supported the subsurface interpretations based on classic seismic interpretation and borehole integration. The improved 3D seismic imaging greatly reduced the uncertainty in seismic-reflection interpretation. Detailed structural and stratigraphic interpretations of the Gabes-Tripoli Basin followed the data pre-conditioning. Initial regional overview interpretations of the Cretaceous-to-recent target intervals precedeed detailed structural and sedimentary analysis that included the detection of sedimentary and tectonic features down to a resolution of few meters. Combined tectonic and stratigraphic interpretations revealed a partial decoupling of overburden faulting in the western and central study area from otherwise dominant basement-rooted strike-slip tectonics. Besides crustal-driven faulting, lateral and vertical evaporite movement in the subsurface was documented as an important process in reservoir development, contributing in places to the development of a high-variability in folding, faulting and fracturing trends.In-depth 3D seismic-reflection interpretation of the Cenozoic sedimentary record of the Gabes-Tripoli Basin finally provided new insights into the lateral extent, geomorphology, internal architecture and age of carbonate platforms in the subsurface of the western offshore Libya. Key stratigraphic targets for subsurface carbonate detection and mapping were the Eocene and the Miocene. Local occurrences of low-to-moderate amplitudes between strong top and base reflectors characterize the Eocene carbonate interval. In this unit, seven distinctive seismic-reflection associations interpreted to indicate subsurface carbonates were observed, classified and mapped. A second distinct carbonate interval is the Miocene. Three distinct seismic-reflection associations interpreted to indicate subsurface carbonate bodies were classified and mapped in this interval. In summary, the research presented in this PhD-thesis fundamentally bases on 3D seismic-reflection analysis integrated with boreholes. The study presents new subsurface sedimentary and tectonic interpretations. It furthermore relates tectonic processes to sedimentary systems development, both fundamentally important for the interpretation of the hydrocarbon system offshore Libya. The research presented is thus important for the understanding the geological evolution of the Gabes-Tripoli Basin, and for future assessment of its petroleum potential.

Institutions

• Division of Earth Sciences and Geography [530000]
• Chair of Geology and Paleontology and Geological Institute [531110]