Source Rock Characterization and Petroleum Systems in North Ghadames Basin, Southern Tunisia

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1 doi: /j x Resource Geology Vol. 61, No. 3: Original Articlerge_163 Source Rock Characterization and Petroleum Systems in North Ghadames Basin, Southern Tunisia Dhaou Akrout, 1 Hassène Affouri, 2 Riadh Ahmadi, 3 Eric Mercier 4 and Mabrouk Montacer 2 1 Laboratory Hydrosciences Appliquées (06/UR/10-03), Higher Institute of Water Sciences and Techniques, University of Gabès, Zrig, Gabès, 2 Laboratory of Organic Geochemistry, Department of Earth Sciences, Sciences Faculty, 3 Laboratory of Eau, Energy and Environment (LR3E), National School of Engineering Sfax, University of Sfax, Sfax, Tunisia and 4 Laboratory of Planetology and Geodynamics (UMR-CNRS 6112), Faculty of Sciences and Techniques, University of Nantes, Nantes cédex, France Abstract This paper presents geochemical analysis of drilled cutting samples from the OMZ-2 oil well located in southern Tunisia. A total of 35 drill-cutting samples were analyzed for Rock-Eval pyrolysis, total organic carbon (TOC), bitumens extraction and liquid chromatography. Most of the Ordovician, Silurian and Triassic samples contained high TOC contents, ranging from 1.00 to 4.75% with an average value of 2.07%. The amount of hydrocarbon yield (pyrolysable hydrocarbon: S2b) expelled during pyrolysis indicates a good generative potential of the source rocks. The plot of TOC versus S2b, indicates a good to very good generative potential for organic matter in the Ordovician, Silurian and Lower Triassic. However, the Upper Triassic and the Lower Jurassic samples indicate fair to good generative potential. From the Vankrevelen diagram, the organic matter in the Ordovician, Silurian and Lower Triassic samples is mainly of type II kerogen and the organic matter from the Upper Triassic and the Lower Jurassic is dominantly type III kerogen with minor contributions from Type I. The thermal maturity of the organic matter in the analyzed samples is also evaluated based on the T max of the S2b peak. The Ordovician and Lower Silurian formations are thermally matured. The Upper Silurian and Triassic deposits are early matured to matured. However, Jurassic formations are low in thermal maturity. The total bitumen extracts increase with depth from the interval m. This enrichment indicates that the trapping in situ in the source rocks and relatively short distance vertical migration can be envisaged in the overlying reservoirs. During the vertical migration from source rocks to the reservoirs, these hydrocarbons are probably affected by natural choromatography and in lower proportion by biodegradation. Keywords: Ghadames basin, hydrocarbon potential, Rock-Eval pyrolysis, saharan platform, source rock, total organic carbon. 1. Introduction A petroleum system is defined as the natural system that encompasses the geologic elements and processes essential for hydrocarbon accumulation and preservation (Magoon & Dow, 1994). The essential elements and processes include a petroleum source rock, maturation of the organic material, a migration pathway for the hydrocarbons to a reservoir rock, and a trap/seal (Magoon & Dow, 1994). Each of these elements must Received 23 December Accepted for publication 6 January Corresponding author: D. Akrout, Laboratory Hydrosciences Appliquées, Higher Institute of Water Sciences and Techniques, University of Gabès, Zrig, 6072, Gabès, Tunisia. dhaou_akrout@yahoo.fr 270

2 Petroleum systems in Ghadames basin, Tunisia Fig. 1 Location map of the study area and the limits of the Ghadames basin (Underdown & Redfern, 2008). take place in time and space so that the organic matter can be converted to petroleum and preserved for extraction. A petroleum system exists wherever these essential elements and processes occur together. The study case chosen is Sud Remada permit in Tunisia (Fig. 1). This region is located in the northern part of the Ghadames basin, which itself is part of the Saharan platform. The referred basin is considered as the largest oil province in northern Africa. It also constitutes one of the hydrocarbon mature basins and therefore is one of the most explored petroleum provinces in Tunisia (Achech, et al., 2001). Several studies have been carried out to explain the exceptional oil reserves in this region. Most geological investigations have been concentrated on the reservoirs and traps. Recent studies of Acheche et al. (2001) and Underdown and Redfern (2008) have focused on the characterization of the petroleum system, the investigation of the stratigraphic position and the spatial distribution of thermally mature source rocks in order to assess the timing and distribution of hydrocarbon. Contrarily to the aforementioned studies, the present investigation focuses more on the details of the oil qualitative aspect by the use of organic geochemistry tools i.e. total organic carbon (TOC) and Rock-Eval pyrolysis, as Felhi et al. (2008) concluded for the Gafsa- Metlaoui basin in south-western Tunisia. Its principal objective is to understand the organic matter types, their depositional environments, the thermal maturity, and the migration processes and direction. 2. Geological setting Petroleum exploration permit Sud Remada is located in the extreme southern Tunisia (Saharan platform) and in the Ghadames basin (Fig. 1). This sedimentary basin is a large depression on the North African platform encompassing more than km 2 over western Algeria, southern Tunisia and north-eastern Libya (Van de Weerd & Ware, 1994; Rudkiewicz et al., 1997; Echikh, 1998; Klett, 2000). The Ghadames basin is characterized by a particular tectonic and stratigraphic evolution (Alem et al., 1998; Echikh, 1998). This area is characterized by the following tectonic history; A regular subsidence during the Paleozoic, followed by the Hercynian compressive event responsible for the uplift and erosion of the Telemzane arch. Consequently the Palaeozoic series was overlain with regional and angular unconformity by the Mesozoic sedimentary rocks (Acheche et al., 2000). Finally, thin Neogene sandstone covered these series with a second major regional unconformity, lacking in Paleogene rocks. Several Palaeozoic formations and especially the Triassic sandstone (TAGI Formation) are known to be the target reservoirs for hydrocarbon explorations in the 271

3 D. Akrout et al. Fig. 2 Lithostratigraphic column of the studied well in southern Tunisia and sample positions. The location of drill hole is shown in Figure 1. Saharan Platform (Underdown & Redfern, 2008). The main oil productive reservoirs are from shallowest to the deepest: (i) TAGI sandstone, middle Triassic, (ii) Acacus Formation (B and A), middle Silurian, and (iii) the El Hammra sandstone (Ordovician). 3. Materials and methods 3.1 Material For this study, a total of 35 drill-cutting samples were selected from different depths and formations (Fig. 2). Samples from the depths up to 1200 m have been drilled by using water based mud, while, samples from the depths deeper than 1200 m are contaminated by oil-mud. The cuttings were the subject of several geochemical analyses and microscopic observations. 3.2 Organic geochemical analysis Cutting preparation The cuttings, contaminated by either oil or water-mud, have undergone several specific procedures to avoid the influences of the geochemical analysis (Fig. 3). The samples drilled with water-based mud were washed carefully with water over sieves in order to remove the mud and all other soluble pollutants. After washing only debris smaller than 5 mm are kept. This precaution is used to eliminate carvings that could be dropped from depths other than the drilled sample. After washing, the samples are kept in humid form to prevent their exposure to high air temperature, which might artificially increase their thermal maturation. The cuttings drilled with oil-based mud are dried at low temperature and washed with chloroform to eliminate the fuel oil (Bordenave, 1993). 272

4 Petroleum systems in Ghadames basin, Tunisia Fig. 3 Standard cuttings preparation procedure for screening analyses Rock-Eval pyrolysis The Rock-Eval II pyrolysis has been performed on the whole set of samples using the reservoir mode (temperature heating ramp: 10 C min -1 ). Besides the classical S1 peak (lith thermovaporizable fraction), this specific mode allows deconvolution of the S2 peak into S2a and S2b peaks, which can be assigned to a heavy thermovaporizable fraction and to an actual pyrolyzable fraction, respectively (Trabelsi et al., 1994) (Fig. 4). The residual organic carbon is oxidized and the resulting CO 2 is recorded as S4 peak. The total organic carbon (TOC) is calculated from the entire set of generated peaks (Espitalié et al., 1985a). These analyses were undertaken in the Organic Geochemistry Laboratory from Entreprise Tunisienne d Activités Pétrolières (E.T.A.P). Rock-Eval T max ( C) is the temperature at the maximum S2b (pyrolysable hydrocarbons, mg HC/g rock) as a function of the thermal maturity (Espitalié et al., 1984; Peters, 1986; Tissot et al., 1987). The hydrogen index (HI) and the oxygen index (OI) are derived from the S2b and S3 parameters, respectively, by normalization to the organic carbon content. The production index (PI) (transformation index) is given by (S1 + S2a)/(S1 + S2a + S2b) (Espitalié et al., 1977) Bitumen analysis The bitumen from powdered samples (30 40 g) was extracted using dichloromethane as solvent (300 Fig. 4 Rock-Eval analysis of cutting sample using the reservoir mode heating program. 400 cm 3 ) for 1 h at 40 C. After that, the filtrated solvent was evaporated (rotary evaporation with water aspirator and evaporation temperature 40 C). Then the extract was concentrated by allowing the oil-solvent solution to stand at room temperature until the CH 2Cl 2 is removed. Organic extract (C 0) was fractionated by a chromatography column ( cm i.d) using silica gel (Blumer, 1957, Fazeelat and Yousaf, 2004). Aliphatics (F1), aromatics (F2) and polar (F3) fractions, were then 273

5 D. Akrout et al. Table 1 Total organic carbon (TOC) and Rock-Eval pyrolysis results of cutting samples from OMZ-2 oil well in the Ghadames basin Age Formation name Sample Depth TOC S1 S2a S1 + S2a S2b S3 PI HI OI Tmax (m) (%) mg HC/g Rock (%) ( C) Jurassic Sbaia Sb Sb Sb Sb Sb Abreghs Abg Abg Abg Abg Abg Abg Horizon B Hb Hb Triassic Bou Sceba BSc BSc BSc BSc Azizia Az Az Az R.hamia RH Silurian Acacus A1C A2C A1B A2B A1A A2A Tannezuft Tnz Tnz Ordovician Tartard Btr Kasba Klg Klg Klg Hammra Hm Sanghar Snhr S3 (mg CO 2/g Rock); HI (hydrogen index) (mghc/gtoc); OI (oxygen index) (mg CO 2/g total organic carbon [TOC]). obtained. Only two fractions from bitumen were eluted by a hexane (F1) and a mixture of hexane/ dichloromethane (65:35 Vol/Vol) (F2). F3 is deduced by the following equation: F3 = C 0 - (F1 + F2). 4. Results and discussion 4.1 Source rock evaluation Hydrocarbon potential The TOC content in sediment is an indicator of the total amount of organic matter presents in the sediment (Ronov, 1958). It is expressed as a weight percent of the total rock. TOC values of cutting samples are listed in Table 1. Most of the Ordovician, Silurian and Triassic samples contain high TOC contents, ranging from 1.00% to 4.75% with an average value of 2.07%. These values indicate a good to very good generative potential according to the Peters scale (Table 2). On the other hand, TOC contents in samples from the Upper Triassic and the Lower Jurassic range from 0.64% to 1.13%, which indicate fair to good generative potential. However, Peters and Cassa (1994) point out that TOC is not always a good indicator of source rock potential because measurements may include inert carbon that has little or no generating potential. The two aforementioned authors believe that the S2 measurement derived from pyrolysis analysis is a better indicator of 274

6 Petroleum systems in Ghadames basin, Tunisia Table 2 Source richness interpretation from total organic carbon (TOC) weight percentage (Peters, 1986) Richness TOC (Wt.%) Poor Fair Good Very good >2.0 Fig. 5 Plot of total organic carbon (TOC, wt %) versus remaining hydrocarbon potential (S2, mg HC/g rock), showing the source rock generative potential. the generative potential of source rocks. The plot of TOC versus S2b has been established in order to get an idea about the quantity of organic matter present and its associated hydrogen. For instance, the set of data shown in Figure 5 confirms that the great majority of Ordovician and Silurian samples are good to very good generative potential and the Triassic samples range from fair to good generative potential and finally Jurassic rocks show a poor generative potential Organic matter type The Van Krevelen plot of hydrogen index (S2b/TOC 100) versus oxygen index (S3/TOC 100) was used to classify the dominant type of organic matter in potential source rocks (Tissot and Welte, 1978; Bordenave, 1993, Fig. 6). Most samples from the Ordovician and Silurian strata show high hydrogen index and low oxygen index. This suggests that the organic matter in Fig. 6 Hydrogen index versus oxygen index diagram with indications for diagenetic evolutionary pathways for type I, II and III organic matter (Espitalié et al., 1977). Plots of the cuttings samples from the studied well (OMZ-2) southern Tunisia. the shale samples contains predominantly Type II marine kerogen, with minor contribution from Type I (oil prone) organic matter. However, the Triassic and Jurassic organic matter is dominantly Type III kerogen, with minor contribution from Type I (Figs 6, 7) Thermal maturity The thermal maturity of organic matter in the analyzed samples is also evaluated based on the T max of the S2 b peak. The maturation range of T max varies with the different types of organic matter (Tissot & Welte, 1984; Espitalié et al., 1985b; Peters, 1986; Bordenave, 1993). The range of variation of T max is narrow for Type I kerogen, wider for Type II and much wider for Type III kerogen due to the structural complexity increasing of the organic matter (Tissot et al., 1987). In our case of study, the pyrolysis T max values for the Ordovician and Lower Silurian samples range from 433 C to 441 C, indicating a mature organic matter (Table 1). Samples collected from the Upper Silurian belonging to the Acacus Formation and from Triassic deposits show T max 275

7 D. Akrout et al. values ranging between 429 C and 433 C. This range of variation indicates an early mature to mature organic matter. However, Jurassic samples exhibit the lowest T max values, varying from 425 C to 435 C, which suggests low thermal maturity. However, the Azizia and Horizon B Formations are distinguished by T max of 441 C and high TOC. These values highlight a source rock that has already passed the diagenesis sensu stricto and reached the oil window. On the other hand, some samples show abnormally low T max values (~415 C) and abnormally developed S1 peak with regard to TOC and the S2b. This is explained by the probable contamination resulting from drilling mud and/or impregnations (Tissot & Welte, 1984; Peters, 1986; Hunt, 1996). Fig. 7 Hydrogen Index values versus maximum pyrolysis temperature (Tmax) of samples analyzed. 4.2 Petroleum system For the samples collected from depth intervals from 500 to 1035 m, the drilling is carried out by using waterbased mud. Subsequently, the cuttings were not contaminated by the oil-mud. These samples, however, show high values of (S1 + S2a/S2b) ratios and PI (around 0.8), and low TOC values (not exceeding 0.5 %) (Fig. 8). Therefore, it is concluded that additional hydrocarbons are present in the sedimentary rocks and majority of them may have been derived by vertical hydrocarbon migration. On the other hand, samples from the 1280 to 2259 m depth interval have an average TOC value of 2% and Fig. 8 Lithologic section and geochemical log for the oil Well OMZ

8 Petroleum systems in Ghadames basin, Tunisia Fig. 9 Lipid extracts versus total organic carbon of cuttings samples from OMZ-2, oil potential raging from 1, poor; 2, fair; 3, good; 4, very good; 5, excellent. high values of (S1 + S2a) and S2b. The T max values range from 431 C to 440 C and PI reached the highest values (0.9). These results support the trapping and the accumulation of hydrocarbon generated from both this rock s interval and that of deeper source rocks. In addition, in this interval, some samples are the low T max values (=414 C) and the (S1 + S2a/S2b) ratio are higher than 10. This result indicates the possible contamination by the drilling fluid. To test this hypothesis, lipid extract was plotted versus the TOC for all samples (Fig. 9). The samples contaminated by oil mud show very good oil potential. Whereas, the samples without contamination have a low to very low potential. This configuration in two main groups indicates the effect of drilling mud contamination and oil migration. The mature zone from the 2550 to 3050 m depth is formed by the Ordovician and Silurian formations. This zone shows the T max values higher than 435 C and high values of (S1 + S2a), S2b, PI and the (S1 + S2a/S2b) ratio. These high values of geochemical parameters suggest that these source rocks have generated and expelled during primary and/or secondary migration of their hydrocarbons to the overlying levels. This hypothesis is confirmed by the dominance of the polar compounds in same maturity levels (Table 3). The values of Pr/Ph, Pr/n-C17 and Ph/n-C18 for analyzed crude oil samples are given in Table 4. Pr/Ph ratios were used to assess the depositional environment (Brooks et al., 1969; Powell & McKirdy, 1973; Didyk et al., 1978). In this study, representative samples Table 3 Extract yields and relative percentage of saturated hydrocarbon, aromatic hydrocarbon and asphaltic compounds of the studied cuttings sample from the well OMZ-2 Age Formation name Sample Depth Total extract Aliphatic HC (F1) Aromatic HC (F2) Asphaltic (F3) (m) (mg g -1 ) Percentage of three fractions Jurassic Sbaia Sb Sb Sb Abreghs Abg Abg Abg Triassic Bou Sceba BSc Azizia Az Az R.hamia RH Silurian Acacus A(1)C A(1)B A(2)B A(2)A Tannezuft Tnz Ordovician Tartard Btr Kesba Klg Leguine Klg Hammra Hm Sanghar Snhr F, fraction (mg g -1 dry weight). F1 + F2 277

9 D. Akrout et al. Table 4 Straight chain alkane and acyclic isoprenoid for the representative samples from well OMZ-2 Age Formation Sample Depth (m) Pr/Ph Pr/nC17 Ph/nC18 Jurassic Horizon B Hb Triassic Azizia Az Ras Hamia RH Silurian Acacus A(1)C ,48 0,58 A(2)B ,58 0,59 A(2)A Tannezuft Tnz Tnz Ordovician Kesba Leguine Klg Hammra Hm Sanghar Snhr probably due to the effects of natural chromatography (geochromatography) and not biodegradation. 5. Conclusion Fig. 10 Relation between isoprenoids and n-alkanes showing source and depositional environments. analyzed from the Ordovician, Silurian, Triassic and lower Jurassic strata show low values of the Pr/Ph ratios. These values are much less than 1.0, which indicates reducing conditions of the sedimentary rocks. The plot Pr/n-C17 versus Ph/n-C18 (Fig. 10) shows that samples are trending to the maturation pole. Therefore, we can distinguish two groups: (i) the first group characterized by Pr/n-C17 ratios > 0.48; and (ii) the second group characterized by Pr/n-C17 ratios < 0.3. The Hm sample is observed in an intermediate position between these two groups. This distribution indicates in situ trapping of saturated hydrocarbons. In addition, the Pr/n-C17 and Ph/n-C18 show two cycles of increase according to burial depth (Fig. 11). The first cycle, starts from 3050 to 2918 m in Ordovician formations, while the second is interested in the depth of 2490 (Tannezuft) to 1745 m (Azizia). This evolution is The main conclusions of this work are summarized as follows. The Ordovician and Silurian formations are good to very good generative potential source rocks in terms of COT and S2b contents. However, Triassic and Jurassic formations display a fair to good and poor generative potential, respectively. The organic matter deposits in the Ordovician and Lower Silurian is predominantly Type II marine kerogen. However, the Triassic and Jurassic organic matter is dominantly type III kerogen with minor contributions from Type I. The thermal maturity of organic matter in the analyzed samples is also evaluated based on the T max of the S2 peak. The Ordovician and Lower Silurian formations are thermally matured. The Upper Silurian belonging to the Acacus Formation and Triassic deposits are early matured to matured. However, Jurassic formations are low in thermal maturity. The Upper Silurian and Triassic formations ( m) have a very good oil potential (free hydrocarbon) and high potential index (PI). These results suggest the trapping and the accumulation of hydrocarbon generated from both the rocks of this interval and deeper source rocks. The total bitumen extracts show enrichment at the level deeper than 1200 m, especially in the m interval, in which total bitumen extracts reached a significant rate. This enrichment indicates that there is in situ trapping of hydrocarbons and/or a short distance of vertical migration to the overlying reservoirs. During their vertical migration from the 278

10 Petroleum systems in Ghadames basin, Tunisia Fig. 11 Stratigraphic log and Pr/Ph-Pr/nC17-Ph/nC18 variations with depth in OMZ-2 oil well. source rocks to the reservoirs, these hydrocarbons are probably affected by geochromatography and some biodegradation. Acknowledgments This work was supported by Research Unit: Geoglob (code: 03/UR/10 02), Science Faculty of Sfax. The Authors are thankful to Moncef SAIDI and Halima bekir-inoubli (Tunisian Company of Petroleum Activity) for Rock-Eval pyrolysis. Our special thanks go to Yasushi Watanabe, PhD, for the helpful comments and suggestions that improved this paper. References Acheche, M. H., M Rabet, A., Ghariani, H., Ouahchi, A., Troudi, H. and Kebaier, D. (2000) Rejuvenated Triassic TAGI play in southern Tunisia, Ghadames basin, North Africa (abs.). AAPG Annu. Conv. Off. Program., 9, A2. Acheche, M. H., M Rabet, A., Ghariani, H., Ouahchi, A. and Montgomery, S. L. (2001) Ghadames Basin, southern Tunisia: a reappraisal of Triassic reservoirs and future prospectivity. AAPG Bull., 85, Alem, N., Assassi, S., Benhebouche, S. and Kadi, B. (1998) Kadi- Controls on hydrocarbon occurrence and productivity in the F6 reservoir, Tin Fouyé-Tabankort area, NW Illizi Basin. Geol. Soc. London Spec. Publ., 132, Blumer, M. (1957) Removal of elemental sulphur from hydrocarbon fractions. Analy. Chem., 29, Bordenave, M. L. (1993) Appleid Petroleum Geochemistry. Editions Technip, 27 rue Ginaux Paris cedex 15, Brooks, J. D., Gould, K. and Smith, J. (1969) Isoprenoid hydrocarbons in coal and petroleum. Nature, 222, Didyk, B. M., Simoneit, B. R. T., Brassell, S. C. and Eglinton, G. (1978) Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. Nature, 272, Echikh, K. (1998) Geology and hydrocarbon occurrences in the Ghadames basin, Algeria, Tunisia, Libya. In D. S. MacGregor, R. T. J. Moody, D. D., Clark-Lowes, eds, Petroleum geology of North Africa. Geological Society London Special Publications, London 132, Espitalié, J., Laporte, J. L., Madec, M., Marquis, F., Leplat, P., Paulet, J. and Boutefeu, F. (1977) Méthode rapide de caractérisation des roches mères, de leur potentiel pétrolier et de leur degré d évolution. Rev. Inst. Français du Pétrole, 32, Espitalié, J., Marquis, F. and Barsony, I. (1984) Geochemical logging. In Voorhees, K. J. (ed.) Analytical pyrolysis: techniques and applications London. Butterworths, London, Espitalié, J., Deroo, G. and Marquis, F. (1985a) La pyrolyse Rock- Eval et ses applications: part1. Rev. Inst. Français du Pétrole, 40, Espitalié, J., Deroo, G. and Marquis, F. (1985b) La pyrolyse Rock- Eval et ses applications: part 2. Rev. Inst. Français du Pétrole, 40,

11 D. Akrout et al. Fazeelat, T., Yousaf, M.S. (2004) Geochemical characterization of outcrop sediments from Dharangi-Upper Indus Basin Pakistan [J]. Jour. Chem. Soc. Pak., 26, Felhi, M., Tlili, A. and Montacer, M. (2008) Geochemistry, petrography and spectroscopy of organic matter of clay-associated kerogen of Ypresian series: Gafsa-Metlaoui phosphatic basin, Tunisia. Resour. Geol., 58, Hunt, J. M. (1996) Petroleum Geochemistry and Geology, 2nd edn. W.H. Freeman, San Francisco, CA. Klett, T. R. (2000) Total petroleum systems of the Trias/Ghadames Province, Algeria, Tunisia, and Libya The-Tanezzuft-Oued Mya, Tanezzuft Melrhir, and Tanezzuft Ghadames. US Geol. Surv. Bull., 2202 A, 15. Magoon, L. B. and Dow, W. G. (1994) The petroleum system. In Magoon, L. B. and Dow, W. G. (eds.) The petroleum system from source to trap American Association of Petroleum Geologists Memoir 60. AAPG, Tulsa, 655. Peters, K. E. (1986) Guidelines for evaluating petroleum source rock using programmed pyrolysis. Am. Asso. Petroleum Geol. Bull., 70, Peters, K. E. and Cassa, M. R. (1994) Applied source rock geochemistry, in Magoon, L.B., and Dow, W.G., eds., The petroleum system-from source to trap. Am. Asso. Petroleum Geol. Mem., 60, Powell, T. G. and McKirdy, D. M. (1973) Relationship between ratio of pristane to phytane, crude oil composition and geological environment in Australia. Nature, 243, Ronov, A. B. (1958) Organic carbon in sedimentary rocks (in relation to the presence of petroleum). Geochemistry, 5, Rudkiewicz, J. L., Robert, D. and Chaouche, A. (1997) Hydrocarbon migration through faults and successive reservoir infilling in the Ghadames basin, Algeria (abs.). AAPG Bull., 81, Tissot, B. P. and Welte, D. H. (1978) Petroleum formation and occurrence-a new approach to oil and gas exploration. Springer Verlag, New York, 538p. Tissot, B. P. and Welte, D. H. (1984) Petroleum formation and occurrence. Springer Verlag, New York, 699p. Tissot, B. P., Pelet, R. and Ungerer, P. H. (1987) Thermal history of sedimentary basins, maturation indices, and kinetics of oil and gas generation. Am. Asso. Petroleum Geol. Bull., 71, Trabelsi, K., Espitalié, J. and Huc, A. Y. (1994) Characterization of extra heavy oil and tar deposits by modified pyrolysis methods. In: European symposium on Heavy Oil Technologies in a Wider Europe, Proceedings, June 7 & 8, 1994, Underdown, R. and Redfern, J. (2008) Petroleum generation and migration in the Ghadames Basin, North Africa: a twodimensional basin-modeling study. AAPG Bull., 92, Van de Weerd, A. A. and Ware, P. L. G. (1994) A review of the east Algerian Sahara oil and gas province (Triassic, Ghadames and Illizi basins). First Break, 12,