Sixth EAGE Eastern Africa Petroleum Geoscience Forum

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The Tanzania margin is dissected by Pemba and Zanzibar islands, unusual structures for a passive margin and which origin is still a matter of debated. In this study, using 2D seismic reflection profiles and five exploration wells, we generate “pseudo-3D” reconstructions of the slope canyon-channel pathways from the Oligocene to Recent. We observe a decrease in slope canyon-channels during the middle-upper Miocene which is interpreted to reflect the onset of the uplift of Pemba Island. The extensional tectonic regime, established since lower Miocene and still ongoing, led the seafloor deformation and reduced sediment supply downslope, progressively disconnecting turbidite channels from their feeding systems. Slope channels offshore Zanzibar were still active at that time, thus indicating that the uplift of this island occurred later, starting from the upper Miocene-lower Pliocene. Changes in seafloor topography also promoted the formation of two newly discovered giant canyons that represent the main sediments conduits for this sector of the western Indian Ocean since the Miocene. Supported by these results, we proposed a conceptual model for the post-Oligocene stratigraphic evolution of the northern Tanzania margin that contemplates a potential relationship between the islands and the East African Rift System.

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In this contribution, we reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to present day. The Seagap fault structure is represented by large scale localized structures affecting the seafloor and displaying growth geometries across most of the post-Miocene sediments. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate those restraining bends are generated by transcurrent structure reactivating Cretaceous structures. By the late Neogene, the Seagap switched to a normal fault kinematic behaviour as testified by the seafloor edge discontinuity’s structure. Seismic mapping, as well as from 2D deep seismic data from literature suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and initially coeval with, the dextral Davie Fracture Zone. Following the cessation of the strike-slip activity on the Davie Transform, the Seagap fault remained active. We discuss the Seagap fault geological and kinematic significance through time and its role within the microplate system in the framework of the East African Rift.

We investigate the role of detachment faults, oblique extension, and structural and thermal inheritance during the rifting of the eastern Gulf of Aden. Our structural approach integrates new seismic interpretations on academic seismic data, previous geological and geophysical data along two representative onshore-offshore sections through the Socotra-Sharbithat segment. We calculate the stretching factors of the different crustal domains (stretched, necking, hyper-extended, exhumed, proto-oceanic and oceanic domains) of the narrow and asymmetric conjugate margins of Socotra and southern Oman.

Total Organic Carbon (TOC) values for deep offshore Lamu wells, range from 0.09 to 2.23 wt % with an average of 0.78 wt %. The average organic richness is higher in the Late Cretaceous (0.83 wt %) than in the Palaeogene (0.65 wt %), Early Cretaceous (0.28 wt %) and Late Jurassic (0.30 wt %). S1 average values for Late Cretaceous are 3.76 mg HC/g rock in Pomboo-1 and 0.31mg HC/g rock in Kubwa-1. S2 average values for Late Cretaceous are 5.00 mg HC/g rock in Pomboo-1 and 0.72 mg HC/g rock in Kubwa-1. Hydrogen index (HI), values vary between 4 and 512 mg HC/g TOC with an average of 157.09 mg HC/g TOC. Organic matters were identified as mixed Types II–III (oil and gas prone) and Type III–IV (gas prone) kerogen in the potential source rocks. The HI and S2 yield values are exceptionally high for the observed TOC values in Pomboo-1. The vitrinite reflectance and Tmax values of deep offshore Lamu range from 0.38 to 0.72% and 360 to 441 degrees celsius, respectively. Vitrinite reflectance maturity favors near coastal region in Upper Cretaceous. The temperatures are still cool for hydrocarbon generation in deep offshore.

Gondwana started to slit up during the Early Jurassic with the separation of Antarctica and Madagascar from Africa, followed by the separation of South America and Africa during the Middle Jurassic. Yet, the structure and overall kinematic evolution of the three major transform fault zones together – the Agulhas, the Davie, and the Limpopo FZ – which control the opening of the major oceanic basins remain poorly studied. The interpretation of an extensive multichannel seismic dataset allows us to provide new constraints on the structure and evolution of these three transform systems. In particular, results show that the Davie and Agulhas transform faults postdate the development of the rift zone-controlling faults whereas the Limpopo margin seems to show an intracontinental transform faulting stage. Moreover, the Davie and Agulhas FZ recorded spectacular inversions during the transform stage whereas transtensional deformation is observed along the Limpopo FZ. This different style of deformation may be explained by two main forcing parameters: (i) the far-field forces that may induce a rapid change of regional tectonic stress, and (ii) the magmatic conditions that may modify the rheology of the crust. In post-drift history, rapid changes in regional tectonic stress are recorded along the Davie system.

The republic of Somaliland is part of a well-recognized hydrocarbon province, the potential of which is epitomized by the Yemeni discoveries of the past 40 years. Although black oil was proven by shallow wells drilled in the Guban Basin in the 1950s, the region is still rather underexplored, with operations restricted to specific areas and time intervals. The lack of activities was mainly due to above-ground reasons, which prevented operators implementing complete technical maturation workflows. Over the last decade, a rejuvenated interest in Somaliland led to the acquisition of new G&G data, which helped disclosing new exploration perspectives and contributed to unlock the potential of the margin.

This paper aims to describe the exploration workflow applied in the Berbera Block, a large concession which lies in the eastern sector of the Guban Basin, from no data to hydrocarbon play and prospectivity definition.

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