Title : Beyond the eastern fringes of Sirte Basin: Prospectivity evaluation and petroleum system assessment of concession 31, Cyrenaica platform, Libya
Abstract:
Concession 31 (Con31) lies in a unique geologic position, with its western part located partly in the Ajdabiya Trough, Amal Platform, the Maragh Trough and Al Quaneen Troughs, the Eastern Sirte Basin, and the eastern part extending onto the Cyrenaica Platform (Fig. 1). The location of Con31 offers key insights to understand how hydrocarbons generated from the mature kitchens of the Sirte Basin (Ajdabiya Trough and Maragh Trough) may have migrated toward relatively underexplored Cyrenaica Platform. Thise study aims to firstly investigate the connection by integrating geological, geophysical, and geochemical data, thereby providing a clear picture of how the tectonic provinces and associated petroleum systems interact and to identify the potential prospectivity and areas attractive for exploration. Secondly, to identify both deep and shallow exploration targets, delineate high and low-risk areas, and investigate the extension of the prospective plays from the Con31 (Eastern Sirte Basin) into the Cyrenaica Platform. Using interpretations of 3D seismic, well log correlations, and geochemical analysis, the study has identified a major fault system and potential carrier beds that may serve as hydrocarbon migration pathways from the Sirte Basin to the Cyrenaica Platform.
The results of the study demonstrate a southwest-northeast migration trend with hydrocarbons sourced mainly from the Maragh and Ajdabiya Troughs and moving toward shallower traps within Con 31 and the Cyrenaica Platform. Geochemical analyses and basin modeling indicate that the area of interest contains multiple source rocks, i.e., the Sirt Shale and age equivalents, with maturities ranging from mid-mature to peak gas generation window. In addition, the lower Cretaceous Middle Nubian Shale, Jurassic and the Triassic Hamin Shale (local source rock) are also identified as contributors to hydrocarbon charge. The Hamin Shale, in particular, appears to be an early-mature source rock that correlates geochemically with oils that are produced from the “F” Field, suggesting the presence of the Triassic source rocks in the southern kitchen area. In the Gicherra area to the south of Con31, the Triassic to Jurassic shales lies within the oil window. Reservoirs include deeper stratigraphic units, such as the Maragh and preCretaceous sandstones that experienced high burial temperatures and as a result aggressive diagenesis, resulting in only moderate reservoir quality. The shallower Tertiary carbonates (e.g., Gir Fm., Gialo Fm., and Sabil Fm.) and Oligocene sandstones (Najah Group) are better reservoirs, as they are diagenetically less altered due to shallow burial depths. Structural configuration of the area of interest is dominated by deep-seated basement involved normal faults that extend into the shallow stratigraphic horizons. Extensional tectonics associated with rifting and gravitational collapse of the Sirte Arch form the main traps, which consist of rollover anticlines and tilted fault blocks.
This structural activity both controlled the formation of traps and acted as vertical conduits for hydrocarbon migration from deeper to shallower stratigraphic intervals via nonsealing faults. The adjacent Cyrenaica Platform has experienced multiple tectonic episodes and remains underexplored with a well density of approximately 1:2000 km². It contains a thick Paleozoic to Tertiary succession, hosting several promising clastic and carbonate plays (Fig. 2). The recent seismic interpretation suggests that it is highly likely that hydrocarbons migrated from the Sirt Basin and may have charged these traps, making the Cyrenaica Platform a promising hydrocarbon exploration province. Overall, this study emphasizes Con 31 is in a transitional petroleum province that links deep trough-sourced hydrocarbons to shallower platform reservoirs. By utilising seismic interpretations, geochemical correlations, and basin modeling, the regional exploration study offers novel perspectives on hydrocarbon charge mechanisms and emphasizes the importance of this area in future exploration efforts along Libya’s Eastern Frontier.
Keywords: Sirte basin, Cyrenaica Platform, Con31, Hydrocarbon Migration, Petroleum System, Hydrocarbon Plays, Geochemistry, Basin Modeling, Exploration Potential.
