Cretaceous oceanic anoxic events (OAEs) recorded in the northern margin of Africa as possible oil and gas shale potential in Tunisia: An overview

Mohamed Soua

ABSTRACT

Significant attention has been given, during the last decade, to Palaeozoic unconventional oil and gas shale in northern Africa where the productive Palaeozoic basins are located. New tentative strategies shed light on Mesozoic unconventional plays represented by Cretaceous shale reservoirs.

In most petroleum systems the proven Cretaceous oceanic anoxic events (OAEs), represented mainly by the Fahdene and Bahloul Formations, played the main role in hydrocarbon generation with good distribution. Their deposition was restricted to the early Aptian (Bedoulian), the early/late Albian, and the Cenomanian–Turonian transition. Additional black shales have been detailed for the first time in Tunisia which relate to the Valanginian Weissert and late Hauterivian Faraoni events. Biostratigraphic and complete geochemical reviews have been undertaken from published papers and unpublished internal reports to better assess these important source intervals. These black shale levels, pertaining to OAEs, were deposited in almost deep marine environments during short-lived periods of anoxia (ca. 2 Ma). In the course of this review, thickness, distribution, and maturity maps have been established for each level using well data from published sources.

KEYWORDS

Oceanic anoxic events; black shale; Cretaceous; Tunisia

http://www.tandfonline.com/doi/abs/10.1080/00206814.2015.1065516

Soua, M. (2016). Cretaceous oceanic anoxic events (OAEs) recorded in the northern margin of Africa as possible oil and gas shale potential in Tunisia: An overview. International Geology Review, 58(3), 277-320.

A Review of Jurassic Oceanic Anoxic Events as Recorded in the Northern Margin of Africa, Tunisia

Mohamed Soua

Abstract 

During these last years, considerable attention has been given to Jurassic oil and gas shale in the middle and high latitudes of the northern hemisphere such as the west Europe and Russian platform where the most attractive Jurassic basins are located (e.g. Cleaveland basin, UK; Boulonnais, northern France; Pechora Basin, Moscow Basin, etc). In most petroleum systems which characterize these basins, the Jurassic (mainly the early Toarcian) played the major role in hydrocarbon generation which constitutes 25% of the global reserve of hydrocarbon. Tunisian basins represented by the northern Tunisian trough, the Dorsale and the North South Axis (NOSA) belong to the southern Tethyan margin where northern and central area have recorded the early Toarcian oceanic anoxic event (T-OAE). This short lived (c. 2 Ma) period of anoxia ranges within the whole Harpoceras serpentinum Zone which corresponds to deep water environments marked by black shale accumulation. Interestingly, towards the south, the dysaerobic conditions in the Chott basin appear to have begun largely later where the oxygen depletion is assumed to have prevailed during the Callovian, whereas it was limited to the early Toarcian in the Central and Northern Tunisia only a few hundreds of kilometers away. In addition, biostratigraphic and complete geochemical review has been undertaken from published papers and unpublished internal reports to better assess these important source intervals. 

Keywords: Early Toarcian Anoxic Event (T-OAE), Callovian OAE, black shale, Jurassic events, Tunisia

http://pubs.sciepub.com/jgg/2/3/4/

Mohamed Soua, “A Review of Jurassic Oceanic Anoxic Events as Recorded in the Northern Margin of Africa, Tunisia.” Journal of Geosciences and Geomatics, vol. 2, no. 3 (2014): 94-106. doi: 10.12691/jgg-2-3-4.

Early Carnian anoxic event as recorded in the southern Tethyan margin, Tunisia: an overview

Mohamed Soua

Abstract

Considerable attention has been given to the Carnian (Late Triassic) Pluvial and Reingraben events associated with organicrich 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 organicrich 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.

Keywords: early Carnian anoxic event; Carnian Pluvial Event (CPE); black shale; Late Triassic; Tunisia

© 2014 Taylor & Francis

http://www.tandfonline.com/doi/abs/10.1080/00206814.2014.967315#.VwhW1nqSST8

Soua, M. (2014). Early Carnian anoxic event as recorded in the southern Tethyan margin, Tunisia: an overview. International Geology Review, 56(15), 1884-1905.

Paleozoic oil/gas shale reservoirs in southern Tunisia: An overview

Mohamed Soua

Abstract

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. 2 Ma) 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 (UN), deep Resistivity (Rt) and Bulk Density (qb) 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.

Keywords: Paleozoic gas/oil shale reservoirs; 

Southern Tunisia; 

Unconventional plays; 

Berkine Basin; 

Jeffara Basin; 

Southern Chott Basin

2014 Elsevier Ltd. All rights reserved
http://www.sciencedirect.com/science/article/pii/S1464343X14002271

Highlights

1. We review the Paleozoic gas/oil shale potential in southern Tunisia.
2. We detail the Rhuddanian, Ludlow–Pridoli and Frasnian Hot shales.
3. We present the essential maps of the three Hot shale levels.

Soua, M. (2014). Paleozoic oil/gas shale reservoirs in southern Tunisia: An overview. Journal of African Earth Sciences, 100, 450-492.