Depositional Environment And Source Potential Of Devonian Source Rock, Ghadames Basin, Southern Tunisia

• Main Authors: S. Mahmoudi, A. Belhaj Mohamed, M. Saidi, F. Rezgui
• Format: Text
• Language: English
• Published: Zenodo 2015
• Subjects: Depositional environment; Devonian; Source rock.; Canada; Rowland; Sheppard; canada basin
• Online Access: https://dx.doi.org/10.5281/zenodo.1100649; https://zenodo.org/record/1100649

Depositional environment and source potential of the different organic-rich levels of Devonian age (up to 990m thick) from the onshore EC-1 well (Southern Tunisia) were investigated based on the analysis of more than 130 cutting samples by different geochemical techniques (Rock-Eval pyrolysis, GC-MS). The obtained results including Rock Eval Pyrolysis data and biomarker distribution (terpanes, steranes and aromatics) have been used to describe the depositional environment and to assess the thermal maturity of the Devonian organic matter. These results show that the Emsian deposits exhibit poor to fair TOC contents. The associated organic matter is composed of mixed kerogen (type II/III), as indicated by the predominance of C29 steranes over C27 and C28 homologous, that was deposited in a slightly reduced environment favoring organic matter preservation. Thermal maturity assessed from Tmax, TNR and MPI-1 values shows a mature stage of organic matter. The Middle Devonian (Eifelian) shales are rich in type II organic matter that was deposited in an open marine depositional environment. The TOC values are high and vary between 2 and 7% indicating good to excellent source rock. The relatively high HI values (reaching 547 mg HC/g TOC) and the low values of t19/t23 tricyclic terpane ratio (< 0.2) confirm the marine origin of the organic matter (type II). During the Upper Devonian, the organic matter was deposited under variable redox conditions, oxic to suboxic which is clearly indicated by the low C35/C34 hopanes ratio, immature to marginally mature with the vitrinite reflectance ranging from 0.5 to 0.7 Ro and Tmax value of 426°C-436 °C and the TOC values range between 0.8% to 4%. : {"references": ["W. TrautMarc, R. D. Boote David, D. Daniel Clark-Lowes \"Exploration\nhistory of the Palaeozoic petroleum systems of North Africa\" in\nPetroleum Geology of North Africa, London, 1998, pp 69- 78.", "M. HediAcheche, A. M'Rabet, H. Ghariani, A. Ouahchi, and Scott L.\nMontgomery \"Ghadames basin, southern Tunisia: A reappraisal of\nTriassic reservoirs and future prospectivity \" AAPG Bulletin, May 2001,\nv. 85, pp. 765-780.", "Marco Vecoli , ArmelleRiboulleau, Gerard J. M. Verstegh,\"Palynology,\norganic geochemistry and carbon isotope analysis of a latest Ordovician\nthrough Silurian clastic succession from borehole Tt1, Ghadames Basin,\nSouthern Tunisia, North Africa\" Palaeoenvironmental interpretation.\nPalaeogeography, Palaeoclimatology, palaeoecology 273, 2009, pp378-\n394.", "G. W. M. Lijmbach, \"On the origin of petroleum.\" Proceedings. Ninth\nworld Petroleum Congress, Vol.2. Applied Sciences Publisher, London,\n1975, pp. 357-369.", "W. K. Seifert & J. M.Moldowan,.\" Paleoreconstruction by biological\nmarkers\". In: Geochimica et Cosmochimica Acta vol. 45, 1981, pp. 783-\n794.", "M. Radke, D. H. Welte, H. Willsch, \"Geochemical study on a well in the\nwestern Canada Basin: relation of the aromatic distribution pattern to\nmaturity of organic matter\". Geochimica and CosmochimicaActa 46,\n1982, pp.1-10.", "R. Alexander, R. I. Kagi, S. J. Rowland, P. N. Sheppard, T. V. Chirila,.\n\"The effects of thermal maturity on distributions of\ndimethylnaphthalenes and trimethylnaphthalenes in some ancient\nsediments and petroleums.\"Geochimica et CosmochimicaActa 49, 1985,\npp. 385\u2013395.", "W. Y. Huang, W. G. Meinschen, \"sterols as source indicators of organic\nmaterials in sediments\" Geochemica et CoschemicaactaActa 40, 1976,\npp. 323-330.", "K. E. Peters, C. C. Walters, J. M. Moldowan, The Biomarker Guide,\nsecond ed. Prentice Hall, New Jersey, 2005.\n[10] G. Ourisson, P. Albrecht, M. Rohmer ''Predictive microbial\nbiochemistry - from molecular fossils to procaryotic membranes.\" TIBS,\n1982, pp. 236-239\n[11] J. Dahl, J. M. Moldowan, M. A. McCaffery and P. A. Lipton, \"A new\nclass of natural products revealed by 3\u03b2-alkylsteranes in\npetroleum.\",Nature 355,1992, pp. 154-157."]}