Regional stratigraphic and facies studies

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.

This study was undertaken by Stefan Lubeseder, supervised by Prof Jonathan Redfern. The aim was to develop a third-order sequence stratigraphic framework for the Silurian and Devonianof North Africa, focusing on Morocco, Algeria, Tunisia and Libya. Due to the stability of the Saharan Craton during this period, Palaeozoic stratigraphy is relatively uniform across the area, allowing a regional study. Palaeozoic rocks form important reservoir and source rocks in North Africa, from the Cambrian to the Carboniferous. A sequence stratigraphic scheme together with the geometry of depositional systems and the key characteristics of their boundaries was developed, which offers as a valuable tool for the prediction of reservoir units in areas beyond data control. The outcrop studies can also serve as analogues to reservoir units in the subsurface. The final PhD thesis contain large inter-regional chronostratigraphic correlation charts, constructed to illustrate the intracratonic depositional model for North Africa.

Practically, the study was split into three parts:

Morocco field case study

Silurian: Silurian sections were studied in the Tafilalt area as well as in the Dra Plain of southern Morocco (Anti-Atlas). The emphasis was on the Ludlowian "Orthoceras" limestones and the so-called "Scyphocrinites" limestones at the Silurian/Devonian boundary. These limestone levels were studied in terms of their biostratigraphic position, depositional system, and inter-regional sequence stratigraphic significance. Silurian "Orthoceras" limestones are known from various other parts of the world and the study provided a significant contribution to the understanding of these beds.

Publications:

Lubeseder, S. (2008). Palaeozoic low-oxygen, high-latitude carbonates: Silurian and Lower Devonian nautiloid and scyphocrinoid limestones of the Anti-Atlas (Morocco). Palaeogeography, Palaeoclimatology, Palaeoecology, 264(1-2): 195-209

Lubeseder, S., Redfern, J., Boutib, L., (2009), Mixed siliciclastic-carbonate shelf sedimentation- Lower Devonian sequences of the SW Anti-Atlas, Morocco Source: Sedimentary Geology, 215, 1-4, pp. 13-32

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:

Stefan Lubeseder 2005: Silurian and Devonian Sequence Stratigraphy of North Africa: Regional?Correlation and Sedimentology (Morocco, Algeria, Libya)

The project commenced in 2006 with a PhD undertaken by Mustafa Karer and supervised by Prof Jonathan Redfern, and was extended to include a field based study led by Dr Stephane Bodin and Prof Jonathan Redfern, with PhD student Jonathan Wood. This latter involved extensive fieldwork in the Murzuk Basin Libya and along the Jeffara Arch (Libya and Tunisa). The research involved collaboration with the LPI Libya and University of Sphax, Tunisia. Aims were to understand the evolving depositional systems, revise the stratigraphy /sequence stratigraphy and characterise /evaluate potential Early Cretaceous reservoirs. The study extended to the subsurface in the Sirt basin, where the "Nubian" sandstones are one of the main reservoir targets. This phase was completed in 2012, with a series of publications and the successful completion of Jonathan Wood's PhD. This project may be extended in future to incorporate further subsurface data, and extend to Egypt and the wider region.

The separate but linked project undertaken by Mustafa Karer (funded by the Libyan government / LPI, with data sponsored by Wintershall) examined the Nubian sandstone and associated igneous activity in the Hameimat Trough, Sirt Basin, Libya. The research utilized high-resolution 3D seismic data, combined with gravity, aeromagnetic, well data and cuttings samples. This project provides valuable insight into seismic imaging of intrusive and extrusive igneous events within the Nubian (Sarir Sandstone) in the Sirt basin, Libya. The presence of volcanics can prove a hazard to drilling, and of emplacement volcanics can have serious detrimental effects on reservoir volume and quality. A number of major oil fields in eastern Sirt basins produce from the Early Cretaceous Nubian sandstone. This significant reservoir is highly structured and has a poorly understood facies distribution. As drilling targets deeper reservoirs or more complex structural areas, developing a better understanding of the Nubian is crucial to successful future exploration. In some localities the Nubian contains significant interbedded volcanics, which have affected and often degraded reservoir quality. The volcanics also affect the seismic response and this makes the exploration program very challenging.

Publications:

Bodin, S., Wood, J., Petitpierre, L., Redfern, J. (2010). " Timing of Early to Mid-Cretaceous tectonic phases along North Africa: New insights from the Jeffara escarpment (Libya-Tunisia)." Journal of African Earth Sciences 58, 3. pp 489-506.

Wood, J.D., S. Bodin, J. Redfern, M.F.H. Thomas, (2014), Controls on facies evolution in low accommodation, continental-scale fluvio-paralic systems (Messak Fm, SW Libya), Sedimentology V 301 p49-69.

PhD Theses:

2009: Mustafa Karer (now with Haliburton Libya): Nubian Sandstones, Hameitmat Trough, Sirte Basin Libya, Evaluating the sedimentology, reservoir characteristics and distribution, and the interbedded igneous units, their origin, distribution and impact on reservoir quality. Libya Gov. Funded

2012 Jonathan Wood (now with Shell International): Sedimentological characterization and regional palaeo-environmental implications of the Messak Fm, SW Libya. NARG Sponsored

The project commenced in 2008 and was led by Dr Sebastian Frohlich (now at Statoil) and Prof Jonathan Redfern, with PhD student Laurent Petitpiere, following an earlier pilot study carried out by Dr Stefan Lubeseder. The project involved extensive fieldwork in Libya on the southern margin of the Ghadames Basin (in part supported by Woodside). Results provide valuable new insights into the depositional environments, and have identified a series of significant incised valleys in the Carboniferous, possible reservoir targets in the subsurface. The work addresses the underlying controls on the system, and refines outcrop to subsurface correlation. In future the project could be extended into the subsurface in Algeria, where these units may offer significant reservoir potential.

Publications:

Fröhlich S., J. Redfern, L. Petitpierre, J. Marshall, M. Power, P. Grech (2009), Diagenesis and reservoir quality evolution of Lower Carboniferous fluvial channels, western Libya) . Journal of Petroleum Geology

Fröhlich, S., Petitpierre, L., Redfern, J., Grech, P., Bodin, S., Lang, S. (2010). "Sedimentological and sequence stratigraphic analysis of Carboniferous deposits in western Libya: recording the sedimentary response of the northern Gondwana margin to climate and sealevel changes." Journal of African Earth Sciences 57 (4), pp. 279-296

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:

2012 Laurent Petitpierre (now with Statoil): Sedimentology and Stratigraphy of the Early Carboniferous Marar Formation in Western Libya. NARG sponsored.

Reports: Preliminary Evaluation of the Carboniferous interval: Dr Stefan Lubeseder pilot study

Mohammed Salem (2^nd year) is funded by the Libyan Government, with data supplied by AGOCO:

The evolution of the Western Sirt Basin in the region of the Dahra Platform, Amin High and Kotla Graben is being evaluated by integrating 2D/ 3D seismic and data from 36 wells. Three tectonic styles can be identified involving regional Pre-rift intra-continental sag, complex multi-stage rifting and modification by wrenching. A major horst-graben system configuration has been delineated, which allows mapping fault distribution and timing throughout the area. Time, interval velocity, isochron, depth, isopach and lithofacies contour maps of the selected (12) horizons have been constructed. These maps are being used to interpret the subsurface architecture of the area from thickness, depth variations and velocity anomalies, in terms of tectonic effect and its control on thickness and facies distribution throughout the Dahra Platform and Kotla Graben area .