E-ISSN : 2541-5794 P-ISSN : 2503-216X Journal of Geoscience, Engineering, Environment, and Technology Vol 01 No 01 2017 Syaifudin M./ JGEET Vol 1 No 1/2016 27 ORGANIC GEOCHEMICAL CHARACTERISTIC OF CRUDE OILS FROM ORANGE GRABEN, SOUTH SUMATRA BASIN M. Syaifudin 1, * 1 Geology- Corresponding author: syaifudin_muhammad@yahoo.com Tel.: 0812-2793-352 Received: Oct 1, 2016. Revised : Nov 15, 2016, Accepted: Nov 20, 2016, Published: 1 Dec 2016 DOI : 10.24273/jgeet.2016.11.3 Abstract Lemat Formation in the Orange Graben in the South Sumatra basin has been considered as syn-rift sediments consist of fluvio-lacustrine sediments, create source rock with fluvio-lacustrine characterize. Based on existing publications, showing that the oils from Orange Graben have fluvio-deltaic characterization and generated by source rock from Talangakar Formation with fluvio-deltaic depositional environment. This paper emphasizes geochemistry methods. Source rock analysis, consist of 26 samples for carbon isotope and 14 samples for biomarker, while oil analysis, consist of 15 samples for carbon isotope and 19 samples for biomarker. Characterization has been based on qualitative and quantitative data. Qualitative data comprise evaluation based on chromatograms and mass-fragmentograms, whereas quantitative data consists of a series of cross-plots, eg. cross plot of carbon isotope δ 13 C saturates - aromatics, distribution of C27-C28-C29 sterane, Pr/nC17-Ph/nC18, Pr/Ph-Pr/nC17, carbon isotope δ 13 C saturates-Pr/Ph, Pr/Ph-total hopane/total sterane, and ratio of C26/C25 (tricyclic). Based on geochemical result of analysis, source rocks of Lemat Formation in the Orange Graben interpret as source rock with fluvio-deltaic characterize, have terrestrial influence while Talangakar Formation in the Orange Graben interpreted as source rock with deltaic characterization, having marine and terrestrial influence. Both of them , consist of humic kerogen. Whereas, oil samples in the Orange Graben interpreted as oilwhich is generated by source rock with fluvio-deltaic characterization, having terrestrial influence, in anoxic-suboxic-oxic conditions, consisting of humic kerogen. Correlation result between source rocks and oils in the Orange Graben, indicating that fluvio-deltaic oil type in the Orange Graben are correlate with not only the source rocks of Talangakar Formations but also with source rock of Lemat Formation. Key words: Geochemistry, Crude Oil, Biomarker, Carbon Isotope, Fluvio-Lacustrine-Deltaic. 1. Introduction South Sumatra Basin is a potential and mature basin for hydrocarbon source. There are a number of sub-basins which is potential as the hydrocarbon source in this basin. Orange Graben is one of sub-basin on the South Palembang Sub- Basin, formed in Upper Cretaceous to Lower Tertiary, in extensional phase, this is the beginning of sedimentation in this area. Lemat Formation in Orange Graben has been considered as syn-rift sediments consist of terrestrial sediment (fluvio-lacustrine), creating source rock with fluvio-lacustrine characterization. While based on existing publications, showing that oil from Orange Graben have fluvio-deltaic characterize and generated by source rock from Talangakar Formation with fluvio-deltaic characterization. This is interesting to study further, especially about possibility of source rock with fluvio- lacustrine characterization in research area. This study emphasized to source rocks of Lemat and Talangakar Formation in Orange Graben, South Palembang Sub-Basin, South of Sumatra Basin. 2. Location of Study Area The study area located in Orange Graben, South of Sumatra (Figure 1). 3. Research Methods The basic source rock analyses comprise screening, kerogen typing, and maturation. Further analysis, such as correlation between source rock and crude oil as well as crude oil to crude oil, has been done by using more sophisticated techniques, i.e. carbon isotope and biomarkers. Source rock analysis, consist of 26 samples for carbon isotope and 14 samples for biomarker, while oil analysis, consist of 15 samples for carbon isotope and 19 samples for biomarker. Characterization has been based on qualitative and quantitative data. Qualitative data comprise evaluation based on chromatograms and mass-fragmentograms, whereas quantitative data consists of a series of cross-plots, eg. cross plot of carbon isotope δ 13 C saturates-aromatics, distribution of C27 C28 C29 sterane, Pr/nC17 Ph/nC18, Pr/Ph Pr/nC17, carbon isotope δ 13 C saturates Pr/Ph, Pr/Ph total hopane/total sterane, and ratio of C26/C25 (tricyclic). 28 Syaifudin M./ JGEET Vol 1 No 1/2016 Fig 1. Location map of the study area and data of source rocks in Orange Graben. The results of this study expected could explain the character of source rocks and oil in the Orange Graben, also to find out the possibility of lacustrine source rock existence and determine the correlation between source rocks and oils in this area, so can be known whether Lemat Formation source rocks also have contributed to produce oil in this area or not. In addition, to provide a new opportunity in the exploration of hydrocarbons in the Orange Graben which considered as a mature and potential basin for hydrocarbon. 4. Regional Geology The evolution of the South Sumatra Basin started in the Mesozoic Era (Pulunggono et al., 1992) (25) as a back-arc basin (Figure 2). Back-arc basins in Indonesia are generally hydrocarbon prolific basins. The mechanism involved in the basin formation is general rifting, which formed a graben or half graben. This basin was formed in two phases, i.e. the rifting phase occured during the Paleogene and the sagging during the Neogene. The rifting phase is characterized by the thinning of crust forming Graben or half Graben, whereas the sagging phase is characterized by stable tectonics, and even a change in tectonic compression, which finished with volcanic activities that are shown by the occurrence of tuff that appeared in the Air Benakat Formation. The rifting phase was filled by the Lahat Group that is comprised of the Benakat and Lemat Formations, whereas the sagging phase was filled with sediments from the Talangakar Formation up to the youngest formation, i.e. Kasai Formation (Figure 3). 5. Characterization of Source Rocks and oils in Orange Graben 5.1. Quantitative Method Pristane/phytane (Pr/Ph) ratios have been used to assess the redox potential of the depositional environment and source of organic matter (Didyk et al., 1978 (10); Tissot and Welte, 1984 (31); Zhang and Huang, 2005 (38); Peters et al., 2005 (22); Duan et al., 2008 (11); Hao et al. 2011 (18); Cheng et al., 2013 (7) and Tao et al., 2015 (9) or reflect the relationship between contributing organisms and the chemistry of the environment (Mello and Maxwell, 1990) (20). Figure 4 shows a cross plot Pr/nC17-Ph/nC18 as proposed by Connan and Cassou (1980) (8) and Pr/Ph Pr/nC17, source rocks of Lemat and Talangakar Formations, and oils in Orange Graben. This image shows both source rocks of Lemat and Talangakar Formation and oils, consists of humic kerogen in suboxic-anoxic until oxic conditions, but mostly in oxic conditions. Waples, 1985 (35) stated that on the average, the stable carbon isotope values of the saturated more negative (lighter) than kerogens. A plot of the stable carbon isotope values of the saturated and aromatic hydrocarbons in the source rocks of Lemat and Talangakar Formations and oils in Orange Graben as proposed by Sofer (1984) (27) is shown in Figure 5. This figure shows source rocks of Lemat and Talangakar Formations and oils consists of terrestrial and mixed material, in anoxic suboxic to oxic conditions, but mostly in oxic conditions. Figure 6 shows a cross plot of Pr/Ph- hopane/sterane and sterane distribution C27, C28, Syaifudin M./ JGEET Vol 1 No 1/2016 29 Fig 2. Tectonic evolution of the South Sumatra Basin from Upper Jurassic-now (Pulunggono et al., 1992). Fig 3. Regional stratigraphy of the South Sumatra Basin (modified from Ryacudu, 2008). 30 Syaifudin M./ JGEET Vol 1 No 1/2016 Fig 4. Cross plot of Pr/nC17-Ph/nC18 and Pr/Ph Pr/nC17, source rocks of Lemat and Talangakar Formation, and oils in Orange Graben. Fig 5. Cross plot of carbon isotope 13 C saturates - 13 C aromatics and carbon isotope 13 C saturates - Pr/Ph, source rocks of Lemat and Talangakar Formation, and oils in Orange Graben. Syaifudin M./ JGEET Vol 1 No 1/2016 31 and C29, source rocks of Lemat and Talangakar Formations and oils in Orange Graben. From this picture it appears that the source rocks of Lemat and Talangakar Formations and oils affected by terrestrial material in anoxic suboxic until oxic conditions, but mostly in high oxic conditions. It is usually believed that C27 steranes derive mainly from phytoplankton and metazoa, whereas C29 steranes mainly originate from terrigenous higher plants (Huang and Meinschein, 1979 (19); Volkman, 1986 (33)). From the cross plot of sterane distribution C27, C28, and C29, show Lemat Formation derived from estuarine to terrestrial environments, whereas Talangakar Formation and oils derived from marine, estuarine, and terrestrial environments. Fig 6. Cross plot of Pr/Ph-hopane/sterane and sterane distribution C27, C28, and C29, source rocks of Lemat and Talangakar Formation, and oils in Orange Graben. Fig 7. Comparison of biomarker characterization qualitatively between source rocks of Lemat and Talangakar Formation, and oils in Orange Graben 32 Syaifudin M./ JGEET Vol 1 No 1/2016 5.2 Qualitative Method Figure 7 is a comparison of biomarker characterization qualitatively between source rocks of Lemat and Talangakar Formation and oils in Orange Graben. From this picture it appears that source rocks of Lemat and Talangakar Formations and oils, according to ten Haven and Schiefelbein (1995) (30); Peters et al. (2005) (22); Syaifudin et al. (2015) (28) and Tao et al. (2015) (29), is not lacustrine sediments because has C26/C25 (tricyclic) smaller than 1. Based on tricyclic data, according to Price et al. (1987) (24), Lemat Formation and oils show terrestrial pattern, whereas Talangakar Formations show marine and terrestrial pattern. Terrestrial is characterized by high C19 and C20 tricyclic (Philp and Gilbert, 1986 (23); Peters and Moldowan, 1993 (21), Hanson et al., 2000 (16); Grice et al., 2001 (14); George et al., 2004 (12); Volk et al., 2005 (32); Zhang and Huang 2005 (38); Peters et al., 2005 (22); Hao et al., 2009 (17); Hao et al., 2011 (18); Asif et al., 2011 (4); Adedosu et al., 2012 (1); Tao et al., 2015 (29); Wang et al., 2015 (34)). Lemat, Talangakar Formation and oils show C19 and C20 tricyclic are more abundant. C23 tricyclic is often the dominant in crude oils of a marine source (Aquino Neto et al., 1983 (2); Zumberge, 1987 (40); Burwood et al., 1992 (6); Hanson et al., 2000 (16); Zhang and Huang, 2005 (38); Hakimi et al., 2011 (15); Tao et al., 2015 (29)). Talangakar Formation besides show C19 and C20 tricyclic dominan, also C23 tricyclic dominan. These data indicate Lemat Formation interpreted as fluvio deltaic sediment, whereas Talangakar Formation having more marine characterization than Lemat Formation. Based on data of 29H and 30H (hopane) distribution, the pattern of 29H <30H indicate marine clastic sediments, while 29H>30H is evaporates-carbonate sediment (Zumberge (1984) (39); Connan et al. (1986) (9); Price et al. (1987) (24); Waples and Machihara (1991) (36); Peters et al. (2005) (22); Hakimi et al. (2011) (15); Xiangchun et al. (2013) (37); Syaifudin et al. (2015) (28), and Wang et al. (2015) (34). The source rocks of Lemat Formation and oils shows 29H <30H, while Talangakar Formation not only show 29H<30H but also show 29H>30H. From data of homohopana distribution which decreased regularly from C31 to C35, interpreted as depositional environment which associated with clastic sediments (Waples and Machihara, 1991 (36)) or more oxidizing conditions (Peters and Moldowan, 1993 (21); Hakimi et al. (2011) (15). The source rock of Lemat, Talangakar Formations, and oils in Orange Graben interpreted as depositional environment which associated with clastic sediments. Based on these data, oil in the Orange Graben interpreted originated from fluvio-deltaic source rocks and has a correlation with Lemat and Talangakar Formations in Orange Graben. 6. Conclusion Source rocks of Lemat and Talangakar Formations and oils in Orange Graben consists of humic kerogen and terrestrial and mixed material. Source rocks of Lemat and Talangakar Formations and oils in Orange Graben, is not derived from a lacustrine sediments, affected by terrestrial material in anoxic -suboxic until oxic conditions, but mostly on high oxic conditions. Besides, its also looks like Lemat Formations derived from estuarine to terrestrial environments, whereas Talangakar Formation and oils in Orange Graben derived from marine, estuarine, and terrestrial environments. Lemat Formation and oils in Orange Graben show terestrial pattern, whereas Talangakar Formations show marine and terrestrial pattern. These data indicate Lemat Formation interpreted as fluvio-deltaic sediment, whereas Talangakar Formation having more marine characteriztion than Lemat Formation. Oils in the Orange Graben interpreted originated from fluvio-delta source rocks, has a correlation with Lemat Formation and Talangakar Formation in Orange Graben. Acknowledgements We would like to thank the management of Directorate General of Oil and Gas and Medco EP for their permission to publish this paper. References [1] T.A. Adedosu, O.O.Sonibare, J.Tuo, O.Ekundayo, 2012. Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria, Journal of African Earth Sciences, 66 67, Elsevier, p 13 21. [2] F.R. Aquino Neto, J.M.Trendel, A.Restle, J.Connan, P.A.Albrecht, 1983. Occurrence and formation of tricyclic and tetracyclic terpanes in sediments and petroleums. In: Bjorøy, M., et al. (Eds.), Journal Advances in Organic Geochemistry, John Wiley and Sons, p 659 667. [3] E.Artono, B.Tamtomo, 2000. Pre Tertiary reservoir as a hydrocarbon prospecting opportunity in the South Sumatra basin, Western Indonesia in the third millennium, AAPG International Conference and Exhibition, Bali, Indonesia. [4] M.Asif, T.Fazeelat, K.Grice, (2011). Petroleum geochemistry of the Potwar Basin, Pakistan: 1. Oil oil correlation using biomarkers, 13C and D, Journal Organic Geochemistry 42, Elsevier, p 1226 1240. [5] M.G.Bishop, 2001. South Sumatra Basin Province, Indonesia: The Lahat/Talang Akar-Cenozoic Total Petroleum System, U.S. Geological Survey, Open- File Report 99-50-s. [6] R.Burwood, P.Leplat, B.Mycke, J.Paulet, 1992. Rifted margin source rock deposition: a carbon isotope and biomarker study of a west African Lower Cr Organic Geochemistry 19, Pergamon Press Ltd, p 41 52. [7] P.Cheng, X.M.Xiao, H.Tian, B.J.Huang, R.W.T.Wilkins, Y.Z.Zhang, 2013. Source controls on geochemical characteristics of crude oils from the Qionghai Uplift in the western Pearl River Mouth Syaifudin M./ JGEET Vol 1 No 1/2016 33 Basin, offshore South China Sea, Journal Marine and Petroleum Geology 40, Elsevier, p 85-98. [8] J.Connan, A.M.Cassou, 1980. Properties of gases and petroleum liquids derived from terrestrial kerogen at various maturation levels, Journal Geochimica et Cosmochimica Acta 44, Pergamon Press, p 1-23. [9] J.Connan, J.Bouroullec, D.Dessort, P.Albrecht, 1986. The microbial input in carbonate-anhydrite facies of a sabkha palaeoenvironment from Guatemala: a molecular approach. Journal Organic Geochemistry 10, Pergamon Press, p 29 50. [10] B.M.Didyk, B.R.T.Simoneit, S.C.Brassell, G.Eglinton, 1978. Organic geochemical indicators of palaeoenvironmental conditions of sedimentation, Journal Nature 272, p 216 222. [11] Y.Duan, C.Y.Wang, C.Y.Zheng, B.X.Wu, G.D.Zheng, 2008. Geochemical study of crude oils from Xifeng oilfield of Ordos Basin, China, Journal Asian Earth Sci. 31, Elsevier, p 341-356. [12] S.C.George, M.Lisk, P.J.Eadington, 2004. Fluid inclusion evidence for an early, marine-sourced oil charge prior to gas-condensate migration, Bayu-1, Timor Sea, Australia, Journal Marine and Petroleum Geology 21, Elsevier, p 1107 1128. [13] Geoservices, 2007. Geochemistry of oil and gas samples from Gegas 1, South Sumatra PSC, Indonesia, PT Geoservices (Ltd), Report No 2007/0606/LAB, prepared for BPMIGAS Medco E and P, not published. [14] K.Grice, M.Audino, R.Alexander, C.J.Boreham, R.I.Kagi, 2001. Distributions and stable carbon isotopic compositions of biomarkers in torbanites from different palaeogeographical locations. Journal Organic Geochemistry 32, Elsevier, p 195 211. [15] M.H.Hakimi, W.H.Abdullah, M.R.Shalaby, 2011. Organic geochemical characteristics of crude oils from the Masila Basin, eastern Yemen, Journal Organic Geochemistry 42, Elsevier, p 465 476. [16] A.D.Hanson, C.Zhang, J.M.Moldowan, D.G.Liang, B.M.Zhang, 2000. Molecular organic geochemistry of the Tarim Basin, north-west China. American Association of Petroleum Geologists Bulletin 84, 1109 1128. [17] F.Hao, X.H.Zhou, Y.M.Zhu, Y.Y.Yang, 2009. Mechanisms for oil depletion and enrichment on the Shijiutuo uplift, Bohai Bay basin, China, American Association of Petroleum Geologists Bulletin 93, 1015 1037. [18] F.Hao, X.Zhou, Y.Zhu, Y.Yang, 2011. Lacustrine source rock deposition in response to co-evolution of environments and organisms controlled by tectonic subsidence and climate, Bohai Bay Basin, China, Journal Organic Geochemistry 42, Elsevier, p 323 339. [19] W.Y.Huang, W.G.Meinschein, 1979. Sterols as ecological indicators, Journal Geochimica et Cosmochimica Acta 43, Pergamon Press, p 739 745. [20] M.R.Mello, J.R.Maxwell, 1990. Organic geochemical and biological marker characterization of source rocks and oils from lacustrine environments in the Brazilian continental margin. In: Katz, B.J. (Ed.), Lacustrine Basin Exploration, vol. 50. American Association of Petroleum Geologists Memoir, 77 97. [21] K.E.Peters, J.M.Moldowan, 1993. The Biomarker guide, Interpreting molecular fossils in petroleum and ancient sediments, Prentice Hall, Englewood Cliffs, New Jersey, 1-363. [22] K.E.Peters, C.C.Walters, J.M.Moldowan, 2005. The Biomarker guide, Cambridge University press, 1- 1155. [23] R.P.Philp, T.D.Gilbert, 1986. Biomarker distributions in oils predominantly derived from terrigenous source material. In: Leythaeuser, D., Rullkötter, J. (Eds.), Advances in Organic Geochemistry 1985. Journal Organic Geochemistry 10. Pergamon, Oxford, 73 84. [24] P.L.Price, T.O.Sullivan, R.Alexander, 1987. The Nature and occurrence of oil in Seram, Indonesia, Proceedings Indonesia Petroleum Association, sixteenth Annual Convention, Jakarta, Indonesia. [25] A.Pulunggono, H.S.Agus, C.G.Kosuma, 1992. Pre- Tertiary and Tertiary fault systems as a framework of the South Sumatra basin; A Study of SAR maps, Proceedings Indonesian Petroleum Association, twenty first Annual Convention and Exhibition, Jakarta, Indonesia, 339-360. [26] R.Ryacudu, 2008. Tinjauan stratigrafi Paleogen Cekungan Sumatra Selatan, Sumatra Stratigraphy Workshop, Ikatan Ahli Geologi Indonesia, 99-114. [27] Z.Sofer, 1984. Stable carbon isotope compositions of crude oils: application to source depositional environments and petroleum alteration, American Association of Petroleum Geologists Bulletin 68, 31 49. [28] M.Syaifudin, E.A.Subroto, D.Noeradi, A.H.P.Kesumajana, 2015. Characterization and correlation study of source rocks and oils in Kuang area, South Sumatra basin: the potential of Lemat formation as hydrocarbon source rocks, Proceedings Indonesian Petroleum Association, Thirty-Ninth Annual Convention and Exhibition, Jakarta, Indonesia. [29] S.Tao, C.Wang, J.Du, L.Liu, Z.Chen, 2015. Geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of NW China, Journal Marine and Petroleum Geology 67, Elsevier, p 460-467. [30] ten Haven and Schiefelbein, 1995. The petroleum systems of Indonesia, Proceedings Indonesian Petroleum Association, twenty fourth Annual Convention, Jakarta, Indonesia, 443-459. [31] B.P.Tissot, D.H.Welte, 1984. Petroleum formation and occurence, second revised and enlarge edition, Springer-Verlag, Berlin-Heidelberg-New York- Tokyo, 1-699. [32] H.Volk, S.George, H.Middleton, S.Schofield, 2005. Geochemical comparison of fluid inclusion and present-day oil accumulations in the Papuan Foreland evidence for previously unrecognised petroleum source rocks. Journal Organic Geochemistry 36, Elsevier, p 29 51. [33] J.K.Volkman, 1986. A review of sterol markers for marine and terrigenous organic matter, Journal Organic Geochemistry 9, Elsevier, p 83 99. [34] G.Wang, X.Chang, T.G.Wang, B.R.T.Simoneit, 2015. Pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks, Journal Organic Geochemistry 78, Elsevier, p 110 120. [35] D.W.Waples, 1985. Geochemistry in petroleum exploration, International Human Resources Development Corporation, Boston, 1-232. [36] D.W.Waples, T.Machihara, 1991. Biomarkers for geologist A Practical guide to the application of steranes and triterpanes in petroleum geology, American Association of Petroleum Geologists Methods in Exploration, No 9, The American Association of Petroleum Geologist, 1-91. [37] C.Xiangchun, T.G.Wang, L.Qiming, C.Bin, T.Xiaowan, 2013. Geochemistry and possible 34 Syaifudin M./ JGEET Vol 1 No 1/2016 origin of petroleum in Palaeozoic reservoirs from Halahatang depression, Journal of Asian Earth Sciences 74, Elsevier, p 129 141. [38] S.Zhang, H.Huang, 2005. Geochemistry of Palaeozoic marine petroleum from the Tarim Basin, NW China: Part 1. Oil family classification, Journal Organic Geochemistry 36, Elsevier, p 1204 1214. [39] J.E.Zumberge, 1984. Source rocks of the La Luna Formation (Upper Cretaceous) in the Middle Magdalena Valley, Colombia, in J.G. Palacas, ed., Geochemistry and Source Rock Potential of Carbonate Rocks, American Association of Petroleum Geologists Studies in Geology #18, Tulsa, 127-133. [40] J.E.Zumberge, 1987. Terpenoid biomarker distributions in low maturity crude oils. Journal Organic Geochemistry 11, Elsevier, p 479 496.