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Soua M.,Entreprise Tunisienne dActivites Petrolieres | Soua M.,Saudi Aramco
International Geology Review | Year: 2014

Considerable attention has been given to the Carnian (Late Triassic) Pluvial and Reingraben events associated with organic-rich shale accumulation in the Germanic basin, Alps, southern Appenines as well as in northwestern Tethyan margins. Less interest has been shown to the southern Tethyan portion represented by the northern margin of Africa, including Tunisia. Tunisian basins represented by the Tellian domain, Tunisian trough, the 'Dorsale', and the North-South Axis (NOSA) belong to the southern Tethyan margin, where northern and central areas record the early Carnian anoxic event within an extensive carbonate platform. This short-lived (~2 million year) period of anoxia ranges within the Aonoides to Austriacum ammonite zones, and corresponds in Tunisia generally to intermediate to shallow water environments marked by organic-rich black limestone, dolomite, and shale. Interestingly, toward the south, the dysaerobic conditions in the Jeffara-southern Dahar basin appear to have prevailed locally also in the early Carnian. Here we review evidence of early Carnian anoxia in Tunisia based on the analysis of more than 17 Triassic sections and wireline logs from several petroleum exploration wells penetrating the black dolomites, limestones, and shales. In addition, biostratigraphic and complete geochemical reviews have been undertaken from published papers and unpublished internal reports to better assess this important and promising hydrocarbon source interval. © 2014 Taylor & Francis.

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was applied to two foraminiferal genera: the biserial Heterohelix, an oxygen-minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the oceanic anoxic event (OAE2) in each studied section were estimated. The fluctuations in abundance of these two opportunistic species can be related mainly to both precessional (ca. 20 kyr) and eccentricity (100 and 400 kyr) cyclicity suggesting that changes in surface water fertility were linked to climate changes in the Milankovitch frequency band.

Salmouna D.J.,Tunis el Manar University | Chaabani F.,Tunis el Manar University | Dhahri F.,Gafsa University | Mzoughi M.,Entreprise Tunisienne dActivites Petrolieres | And 2 more authors.
Journal of African Earth Sciences | Year: 2014

The Turonian-Coniacian series of Bireno and Douleb Members (carbonate Members of the Aleg Formation) have been examined on their sedimentology, stratigraphy and faunistic contents to provide new insights into the paleoenvironment evolution and sea-level changes in the Gafsa basin. At this scale, both the Turonian-Coniacian series are mainly made of marls and limestones and locally include evaporites. In this paper, ostracods together with benthonic and planktonic foraminifers, collected from the Upper Cretaceous series of Berda and Chemsi mountains, are used to provide some chronostratigraphic precisions (age and limits) of these lithostratigraphic units. Accordingly, four lithostratigraphic units, belonging to the Aleg Formation, were recognized following an ascending order; the Annaba Member (Lower Turonian), the Bireno Member (Lower Turonian-Middle Turonian), the Lower Aleg Marls (Middle Turonian-Upper Turonian, Jebel Chemsi and Upper Turonian-Lower Coniacian, Jebel Berda) and the Douleb Member (Coniacian). These units are overlaid by the Upper Aleg marls Santonian in age.The recognized microfacies are interpreted as a shallow marine deposit of a lagoonal environment, shallowing upward from supratidal to subtidal settings with scattered rudistic patch reefs. The corresponding carbonate sediments were affected by several diagenetic stages starting at the sea floor (early diagenesis), continuing near the surface (meteoric diagenesis) and ending in the subsurface (burial diagenesis). © 2014 Elsevier Ltd.

Soua M.,Entreprise Tunisienne dActivites Petrolieres
Journal of African Earth Sciences | Year: 2014

During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya, Mouydir, etc.). In most petroleum systems, which characterize these basins, the Silurian played the main role in hydrocarbon generation with two main 'hot' shale levels distributed in different locations (basins) and their deposition was restricted to the Rhuddanian (Lllandovery: early Silurian) and the Ludlow-Pridoli (late Silurian). A third major hot shale level had been identified in the Frasnian (Upper Devonian). Southern Tunisia is characterized by three main Paleozoic sedimentary basins, which are from North to South, the southern Chotts, Jeffara and Berkine Basin. They are separated by a major roughly E-W trending lower Paleozoic structural high, which encompass the Mehrez-Oued Hamous uplift to the West (Algeria) and the Nefusa uplift to the East (Libya), passing by the Touggourt-Talemzane-PGA-Bou Namcha (TTPB) structure close to southern Tunisia. The forementioned major source rocks in southern Tunisia are defined by hot shales with elevated Gamma ray values often exceeding 1400 API (in Hayatt-1 well), deposited in deep water environments during short lived (c. 2Ma) periods of anoxia. In the course of this review, thickness, distribution and maturity maps have been established for each hot shale level using data for more than 70 wells located in both Tunisia and Algeria. Mineralogical modeling was achieved using Spectral Gamma Ray data (U, Th, K), SopectroLith logs (to acquire data for Fe, Si and Ti) and Elemental Capture Spectroscopy (ECS). The latter technique provided data for quartz, pyrite, carbonate, clay and Sulfur. In addition to this, the Gamma Ray (GR), Neutron Porosity (ΦN), deep Resistivity (Rt) and Bulk Density (ρb) logs were used to model bulk mineralogy and lithology. Biostratigraphic and complete geochemical review has been undertaken from published papers and unpublished internal reports to better assess these important source intervals. © 2014 Elsevier Ltd.

Haddad S.,Entreprise Tunisienne dActivites Petrolieres | Echihi O.,Entreprise Tunisienne dActivites Petrolieres | Ben Jemia H.,Entreprise Tunisienne dActivites Petrolieres
Society of Petroleum Engineers - North Africa Technical Conference and Exhibition 2013, NATC 2013 | Year: 2013

Integrated study was carried out on the Jeffara basin in order to understand and discuss the geometry and the key levels as well as Petroleum System elements on the Jurassic strata. The studied area lies as N140-130 trending down faulted area roughly parallel to the coastline; it was developed mainly in response stage of Tethyan rifting. The subsurface data reveal that most of the structuring is amplified by halokinesis and the salt piercement of the entire sedimentary cover in the southeast area. The Mrabtine Formation, which is represented by a mixed siliciclastic and carbonate deposits, is considered to be the best Jurassic potential reservoir rock in the Jeffera basin. The Callovian shales appear to contain the best potential for source rock off all units in the Jurassic, showing poor to good TOC contents (up to 3.27% TOC) and good petroleum potential up to 10 kg of HC/ton of rock. The kerogens are mainly type II algal material and mix type II and III with locally higher type III organic material in El Bibane and Jerba area. Several prospects and leads have been identified at the top of the Mrabtine Formation, these structures are extensional fault related (horsts or tilted fault blocks) with a NW-SE orientation. The northern part of the Jeffara basin shows several attractive fault related traps but sedimentological and stratigraphic studies indicate that there would be a risk of poor reservoir characteristics, a lack of source facies and top seal. The southern domain contains fewer structures and leads but more attractive plays with the proven hydrocarbon accumulations of the Ezzaouia and El Biban Fields. Copyright 2013, Society of Petroleum Engineers.

Soua M.,Tunis el Manar University | Ghanmi M.,Tunis el Manar University | Turki D.Z.,Tunis el Manar University | Turki M.M.,Tunis el Manar University | And 2 more authors.
Society of Petroleum Engineers - North Africa Technical Conference and Exhibition 2013, NATC 2013 | Year: 2013

Searching for new challenges and exploration strategies, new-old techniques used abusively in the Gulf of Mexico (sub-thrust and sub-salt exploration) are applied for the first time in Tunisia. Beginning with the Sub-thrust prospectivity: In Central Tunisia North-South Axis (NSA) and Kairouan areas, 2-D seismic acquisition shows series of high-angle reverse and thrust faults running through NE-SW trend across the area forms the boundary between the uplifted Atlas Foothills terrain to the northwest and the low lying Pelagian Basin to the southeast. Alternatively, in Kairouan area (in the sub-surface), four investigated wells show a number of drilled thrusted hanging-wall structures. Basin modeling analysis using Basin Mod 1D; 2D and Basin view as well as seismic interpretation prove the existence of a theoretical potential on the sub-thrust footwall of these faults to the southeast, where they could be sourced directly from the Pelagian Basin. Seismic lines show Cretaceous and Tertiary sediments dipping away from these faults into the basin. Potential reservoirs are the Ypresian El Garia (nummulitic limestone fades) and the Campanian Abiod formations they could be reservoir targets for this play. However, 2D seismic surveys are very limited and are of poor quality at present, but some initial lead areas have been already defined For the Subsalt prospectivity: targets are very poor understood in the northern African domain (Algeria, Tunisia and Libya). Using basin modeling and seismic data, several salt-canopies like structures have been identified and several leads have been defined notably in the southern Gulf of Gabes and in Gulf of Tunis. Copyright 2013, Society of Petroleum Engineers.

Soua M.,Entreprise Tunisienne dActivites Petrolieres | Smaoui J.,Entreprise Tunisienne dActivites Petrolieres | Zaghbib-Turki D.,Tunis el Manar University
North Africa Technical Conference and Exhibition 2010, NATC 2010 - Energy Management in a Challenging Economy | Year: 2010

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was tested and applied on two foraminiferal species: the biserial Heterohelix, an oxygen minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the second Oceanic Anoxic Event OAE-2 in each studied section were estimated. Alternatively, the fluctuations of these two opportunistic species can be related mainly to both precessional (23-19 ka) and eccentricity (414-106 ka) cyclicity suggesting that changes in surface water fertility were linked to the Milankovitch parameters. Copyright 2010. Society of Petroleum Engineers.

Sous M.,Entreprise Tunisienne dActivites Petrolieres
SPE Middle East Oil and Gas Show and Conference, MEOS, Proceedings | Year: 2013

Through this last decade numerous wells have been drilled to the Ordovician in southern Tunisian Ghadames basin. They have met mudlog gas as well as mudlog oil shows in one or several sandstone levels. Some producing wells from the Silurian section display log pay in the Ordovician but seem to be off to the mapped Ordovician depth structural closure. Alternatively, large 3D seismic survey has been undertaken in southern Tunisia in order to map the Ordovician. Isochore, isopachs and isobaths maps have been generated on four (04) main reservoir intervals all of which have produced from several fields in the Ghadames Basin (including Algeria and Libya). These reservoirs are (1) Jeffara, (2) Bir Ben Tartar, (3) Kasba Leguine and (4) Sanghar Formations (Tunisian nomenclature). In Southern Tunisia the Upper Jeffara sandstones, the Jeffara sandstones and the Bir Ben Tartar are classified as the primary reservoir intervals. Generated isochore map of the upper Jeffara sandstones, has been used as evidence of a "geant" Tunnel valley shape in relationship with other valley structures pertaining to the Libyan side. As the Ordovician sandstone reservoirs in Tunisia have poor reservoir quality but locally some intervals have tested condensate, some fields have proved that syn-glacial deposits form a gas reservoir (e.g. Tiguentourine field in south-eastern Algeria). Within such facies, the Ordovician has tested gas and/or condensate from a number of wells in the Ghadames basin. This proposal will involve the existence of valley-fill sandstones pertaining to the Jeffara formation in southern Tunisia giving evidence of sub-glacial environment of deposition where iceproximal glaciofluvial deposits form the highest quality reservoirs using (1) isochore and isopachs maps of the Ordovician, (2) core analyses, (3) cyclostratigraaphy and (4) chemostratigraphy (major and trace elements). This will enhance the exploration activity for the Ordovician in southern Tunisia. Copyright 2013, Society of Petroleum Engineers.

Zaghbib-Turki D.,Tunis el Manar University | Soua M.,Entreprise Tunisienne dActivites Petrolieres
Journal of African Earth Sciences | Year: 2013

High-resolution foraminiferal biostratigraphic analysis has been undertaken on the Bahloul Formation, in Bargou, Jerisa, Guern Halfaya (Central Tunisia), Kherij (North-eastern Tunisia) and Gafsa (southern Tunisia) sections, which prove the preservation of the worldwide expression of the Cenomanian-Turonian transition (C-T) Oceanic Anoxic Event (OAE2). This study confirms that the OAE2 was rather a long-term global event. The high resolution biostratigraphical analysis has allowed subdividing the Whiteinella archaeocretacea zone of the standard biostratigraphic scheme. The ability to apply same subzones in both Tethyan and transitional/Boreal provinces during the C/T boundary has important palaeobiogeographical and palaeoecological implications. The palaeoecological framework shows that the OAE2 development is composed of several successive phases. In addition, a faunal turnover during the W. archaeocretacea zone interval is recorded. However, we confirm that the faunal turnover in the W. archeocretacea zone did not result in a loss of biodiversity, but rather in replacement through originations. © 2012 Elsevier Ltd.

The late Cenomanian-early Turonian deposits in Tunisia recording the OAE2 event are commonly attributed to the Bahloul Formation. These deposits are composed of dark clayey limestone and organic-rich black shales with abundant planktic foraminifera. At the Bargou area, Oued Kharroub section, these organic-rich deposits include siliceous beds with abundant radiolarians recalling the "Livello Bonarelli". A total of 25 radiolarian species are identified with a maximum of 18 species per sample. Moreover, the species skeleton preservation is usually poor to moderate in the most studied samples [estimated preservation index (PI) values ranging between 4 and 6]. Two successive assemblages are distinguished. The oldest one (RI) is dominated by nassellarians, which includes mainly Stichomitra, Pseudodictyomitra and Rhopalosyringium genera. It is included within the upper part of foraminiferal Rotalipora cushmani Zone and lower part of Whiteinella archaeocretacea zone. In contrast, the youngest assemblage (RII), which belongs to the upper part of the W. archaeocretacea zone and the earliest Turonian Watinoceras ammonite assemblage, is dominated by spumellarians and includes mainly Archaeocenosphaera, Cavaspongia, Pseudoeucyrtis and Pyramispongia genera. In addition, major and trace elements are analysed to test whether the geochemical record was synchronous to the biotic event or not. Thus, selected crossplots, Al2O3 vs. SiO2 and Al2O3 vs. TiO2, are used to evaluate the detrital input, and V/Cr vs. V/(V + Ni) and U/Th vs. V/(V + Ni) are used to evaluate the bottom redox conditions and the primary productivity within the Bahloul Formation. A strong Si/Al increase is marked in the lower part of the siliceous and organic-rich Bahloul Formation that could be explained by a local increase in upwelling-related biogenic SiO2 (silica-secreting organisms). Relative low abundance of terrigenous-related Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba (organic matter related trace elements) suggests that the Bahloul was of relatively elevated primary productivity and minimal detrital input. Enrichments in redox-sensitive trace metals U and V in the Bahloul Formation deposits and redox indices, such as V/(V + Ni), U/Th and V/Cr, indicate that oxygen-restricted conditions prevailed during the late Cenomanian-earliest Turonian times and correlate well with relative abundances of some radiolarian and foraminiferal paleo-environmental indicators. In addition, indicators of detrital flux variations are used. Al2O3 shows a slight positive correlation with TiO2 and a less distinct correlation with SiO2. © 2011 Saudi Society for Geosciences.

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