Basin evolution and source to sink

Moroccan Atlantic Margin has experienced km-scale vertical movements during its post-rift evolution. Uplifts have controlled the distribution of sedimentary systems and the origin of the sediments delivered to the margin. Untangling the complex post-rift evolution of the NW African margin is fundamental to constraining the behaviour of the shallow-marine to fluvial transition zone as well as the formation and distribution of potential reservoirs

The Lower Cretaceous shallow-marine to fluvial coarse siliciclastic successions of the Agadir Essaouira Basin are an exploration target offshore. However, limited success in recent drilling campaigns reflects the poor understanding of the depositional systems from source to sink. and its links to the eroding hinterland. This highlights the need of a more holistic approach, tracing sediment routing and the main input points through time.

This integrated study aims to develop the first regional paleogeographic and tectonostratigraphic Source-to-Sink model of North-West Africa by deciphering the controls, timing and volume of the sediment supply to the margin and by constraining the importance of sediment recycling, mixing and storage. The main focus is on the late Early Cretaceous marine regression that is associated with substantial input of clastic sediment into the deep-water basins.

The study is currently focusing on source discrimination based on the heavy mineral populations of the potential source areas and on the sampled sandstones in combination with apatite and zircon geochronology.

This study is carried out under the supervision of Stefan Schroeder and Jonathan Redfern (University of Manchester), Shane Tyrrell (NUI Galway) and Giovani Bertotti (TU Delft)

An interdisciplinary and multi-scale research project to characterize and evaluate the evolution of the Cretaceous depositional systems Onshore Morocco along the Atlantic Seaboard, extending offshore along the Morocco passive margin. To improve understanding of the depositional systems, facies modeling and basin evolution, with the implications for petroleum systems and modeling reservoirs, source distribution , generation and migration, and seal. The research will undertake detailed analysis of onshore outcrops to develop improved sedimentological models and establish depositional facies distributions through time, provenance, diagenesis and improved chronostratigraphy.

This project commenced in January 2014, and 1^st results have been delivered to the sponsors. The project will be integrated with analysis of available offshore subsurface data provided by ONHYM, including an offshore 2D seismic grid and access to well data and reports. NARG has singed an MOU with ONHYM to cooperate ion this study, building on the very strong links over the last 10 years. Additional data will be provided by sponsoring companies, to assist in mapping the offshore in order to constrain the source to sink models, and assess the evolution of the Cretaceous system and controls on sedimentation (salt tectonics) and basin evolution.

Research team comprises 6 PhDs (Tim Luber, Angel Arantegui, Tu Anh Ngyeun (Schlumber Scholarship), and Leonardo Muniz Pichel (Brazilian Gov Scholarship) based in Manchester and Remi Charton in TuDelft. Academic staff supervision from Prof Jonathan Redfern, Prof Giovanni Bertotti and Prof Joep Storms from Manchester, TU Delft and Amsterdam (VUA).

The study will focus on stratigraphic architecture, paleogeography and facies trends of Jurassic carbonates along the Moroccan Atlantic Margin, as well as age relationships in the basin.

Part of the work will be outcrop-based, by conducting a regional stratigraphic-sedimentological study. Results will be integrated with subsurface datasets, seismic and well data.

The study will have impact on active oil and gas exploration, in the light of hydrocarbon discoveries in Jurassic carbonates both in Morocco and in the conjugate basins of Canada. Reconnaissance studies of the Jurassic Outcrops north of Agadir have already been conducted.

Students are being interviewed for an early January start. In addition ONHYM are funding one of their staff to undertake an MRes at Manchester as part of this study.

Early work on regional source rocks was undertaken by postdoctoral researcher Dr Sebastian Luning, supported by Stefan Lubeseder and Dr Jonathan Redfern. This work aimed to assess the source rock quality of Palaeozoic shales from outcrop studies, that had proved difficult to quantify due to intense weathering. The project included the analysis of a number of methods to allow more accurate regional mapping of source rock facies including surface exposures. Based on their characteristic uranium gamma-radiation and pyrite framboid distribution, the original organic richness of the Silurian / Upper Devonian shales in weathered outcrops was mapped in Libya. A model for the distribution of the rich source rocks was developed. Fieldwork was carried in the Moroccan Anti-Atlas where the Frasnian and Silurian hot shales were studied at outcrop using a portable gamma-ray spectrometer. The unit is typically marked by enrichment in uranium. Additional fieldwork was carried out on the Silurian Tannezuft Shales outcrops documented in Ghat (SW Libya) and Algeria for the Silurian and Devonian source facies.

The project was continued by Dr Alvaro Jimenez Berracosso (now with Repsol). New field investigations were carried out in north central Tunisia, examining the organic-rich sediments of the Bou Dabbous Fm (lower Eocene). The research addressed the controls on the development of the organic richness and assess its distribution stratigraphicaly and aerially, in order to improve source rock quality predictions.

Other research (oncluding proprietary consulting projects) has focused on the Silurian (Tanezuft Shales) in Libya and Morocco, Cenomanian/ Turonian and Toarcian source rocks.

Future work will initially focus on the Cenomanian / Turonian in Morocco, with Prof Kevin Taylor from the University of Manchester. These outcrops, integrated with available offshore well and seismic data, will provide an analogue for offshore source intervals along the Atlantic margin. Development of the online database is continuing for all the main source horizons and potentially significant intervals.

NARG has also been working on basin modelling projects, integrated to petroleum system analysis, since its inception. We have access to the lasts basin modelling software, and through collaborations, can undertake heat flow and subsidence history analysis (FT, Vr etc). The capability is enhanced now through the membership of TU Delft.

Publications:

Burwood R., Redfern J., and Cope M. (2003) Geochemical evaluation of East Sirte Basin (Libya) petroleum systems and oil provenance. In Petroleum Geology of Africa: New Themes and Developing Technologies, Vol. 207 (ed. T. J. Arthur, D. S. MacGregor, and N. R. Cameron), pp. 203-204. Geological Society of London Special Publication.

Lüning, S., Craig, J., Loydell, D. K., Storch, P. & Fitches, W. R. (2000): Lowermost Silurian 'hot shales' in North Africa and Arabia: Regional Distribution and depositional model. Earth Science Reviews 49: 121-200.

Lüning, S., Adamson, K., Craig, J. (2003a): Frasnian 'Hot Shales' in North Africa: Regional Distribution and Depositional Model. In: Arthur, T. J., Macgregor, D. S., Cameron, N. (Eds.), Petroleum Geology of Africa: New Themes and developing technologies, Geol. Soc. (London) Sp. Publ. 207: 165-184.

Lüning, S., S. Kolonic, D. Loydell, J. Craig (2003b): Reconstruction of the original organic richness in weathered Silurian shale outcrops (Murzuq and Kufra basins, southern Libya). GeoArabia 8: 299-308.

Lüning, S., S. Kolonic, E. M. Belhadj, Z. Belhadj, L. Cota, G. Baric, T. Wagner (2004): Integrated depositional model for the Cenomanian-Turonian organic-rich strata in North Africa. Earth-Science Reviews 64: 51-117.

Underdown, R., and Redfern, J., (2007), The importance of constraining regional exhumation in basin modelling: a hydrocarbon maturation history of the Ghadames Basin, North Africa., Petroleum Geoscience, V 13, p 1-19

Underdown, R., and Redfern J., (2007), Constraining the burial history of the Ghadames Basin, North Africa: An integrated analysis using sonic velocities, vitrinite reflectance data and apatite fission track ages. Basin Research, Volume 19, Number 4, pp. 557-578 (22)

Underdown, R., and Redfern, J., (2008), Petroleum Generation and Migration in the Ghadames Basin, North Africa: A 2D Basin Modelling Study, AAPG Bulletin, V. 92, No. 1 , pp. 53-76.

Bodin S., E. Mattioli, S. Frohlich, J.D. Marshall, L. Boutib, S. Lahsini, J.Redfern (2010). "Toarcian carbon isotope shifts and nutrient changes from the Northern margin of Gondwana (High Atlas, Morocco, Jurassic): Palaeoenvironmental implications." Palaeogeography, Palaeoclimatology, Palaeoecology, 297, pp 377-390.

Reports:

Additional reports are available of the Jurassic source rocks of Fuerteventura, and regional source rock analysis of the Silurian in Morocco and Libya.

PhD Thesis:

2006: Dr Ruth Underdown (now a school teacher): Assessing the impact of regional unconformities on the maturation and migration of hydrocarbons within the Ghadames Basin, North Africa. NARG Funded.

The Numidian Flysch is the most widespread tectono-stratigraphic unit in the western Mediterranean. It outcrops in the Alpine nappe belt, in southern Spain, Morocco, Algeria, Tunisia, Sicily and southern Italy. In Sicily and Tunisia it is an Oligocene to mid-Miocene flysch-type deposit sourced from the north-African passive margin and deposited into an east-west trending foreland basin. This study was supervised by Dr Stephane Bodin and Prof Jonathan Redfern, and undertaken as a PhD by Myron Thomas (now Shell). The study focused on outcrops in northern Sicily and Tunisia, evaluating the sedimentology and provenance within the context of the basin as a whole. Special emphasis is placed upon the controls on deposition and provenance of the clastic supply, which until this study were largely unknown. Future work is intended to extend this study to the west into Algerian and Morocco.

Publications:

Thomas, M. F. H., Bodin, S., Redfern, J., Irving, D. H. B. (2010). "A constrained African craton source for the Cenozoic Numidian Flysch: Implications for the palaeogeography of the western Mediterranean basin." Earth Science Reviews 101, 1. pp 1-23.

Thomas, M.F.H., S. Bodin, J. Redfern Comment on European provenance of the Numidian Flysch in northern Tunisia'by Fildes et al.(2010) Terra Nova 22 (6), 501-503

Lubeseder S., J. Redfern, L. Petitpierre, S. Fröhlich. (2011). Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya). Geological Society, London, Petroleum Geology Conference series 2011, v. 7, p. 725-734, doi: 10.1144/?0070725

PhD Thesis:

2011: Dr Myron Thomas (now with Shell International): Sedimentology of the Nummidian Flysch - NARG Sponsored.

Kara English (2^nd Year) is funded by (and works for) Petroceltic (providing data and funding).

This study focuses on the southern Illizi basin in Algeria, where a substantial new dataset has been acquired by Petroceltic International as part of the recent appraisal of the Ain Tsila gas-condensate discovery. A number of complementary methods are being used to constrain the thermal and burial history of the Ordovician reservoirs in the Ain Tsila field.

These techniques include: estimates of missing stratigraphy based on regional observations and cross-sections, estimates of the magnitude of exhumation based on sonic velocity 'over-compaction' of regionally homogeneous shale and sandstone packages, estimates of peak burial temperature and paleo-geothermal gradients based on vitrinite reflectance data, and constraints on thermal history provided by apatite fission track (AFT) data.

The resulting burial history models combine all available fluid inclusion and source rock data to generate a model of the timing of hydrocarbon generation and migration from the primary source rocks within the basin. These models are being used to predict the timing of a potential early-oil fill within the Ordovician reservoirs in the Ain Tsila field, and also the timing of the main gas- condensate charge.

These burial history models will be utilized in order to construct some conceptual sandstone diagenesis models using Touchstone software, and to determine if any predictions can be made regarding the (spatial and vertical) variation of reservoir quality across the Ain Tsila field.