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Organic Facies Characteristics of the Miocene Soma Formation (Lower Lignite Succession-KM2), Soma Coal Basin, Western Turkey
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 76 (2015) 27 – 32
European Geosciences Union General Assembly 2015, EGU Division Energy, Resources & Environment, ERE
Organic facies characteristics of the Miocene Soma Formation (Lower Lignite Succession-KM2), Soma Coal Basin, western Turkey Selin Hokerek*, Orhan Ozcelik Department of Geological Engineering, Akdeniz University, Antalya,07058, Turkey
Abstract The Soma coal basin is one of the largest economic lignite-bearing alluvial basins of western Turkey. The Miocene succession of the coalfield contains two lignite seams successions; Lower Lignite, Middle Lignite. Kerogen in the deposits is type III, as indicated by organic petrographic observations and Rock-Eval data. Total organic carbon (TOC) values are between 28.45 and 73.38% in the formation. Tmax values vary between 403 and 429°C, confirming maturation trends indicated by vitrinite reflectance data (between 0.35-0.48 Ro%). Organic facies type C and CD were identified in the investigated units. The organic matter is partly oxidized/oxidized and reworked. © 2015 2015 The byby Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license © TheAuthors. Authors.Published Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the GFZ German Research Centre for Geosciences. Peer-review under responsibility of the GFZ German Research Centre for Geosciences
Keywords: Western Turkey; Bakırçay Graben; Soma Formation; organic facies; organic geochemistry
1. Introduction The study area is located within Western Anatolian extensional province (WAEP) characterized by numerous E– W grabens and NNE-trending basins. The lignite bearing sedimentary basins in Western Anatolia arose resulting
* Corresponding author. Tel.: +90-242-310-4307; fax: +90-242-310-6306. E-mail address: [email protected]
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the GFZ German Research Centre for Geosciences doi:10.1016/j.egypro.2015.07.836
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Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
from intra-continental extensional tectonic regime developing in Miocene (Fig.1). These lignite basins are bound by growth faults and contain sedimentary and volcanic rock assemblages [1]. The geology of the Soma coal basin was described and illustrated in detail earlier [2, 3, 4, 5, 6, 7, 8]. A simplified geologic map southern Soma and generalized stratigraphic sequence of the Soma basin are depicted in Fig. 2. The Soma and Denis Formations, which were characterized by nonmarine, laterally extensive, and lacustrine units dominated by limestone, marl, and claystone, form the sedimentary sequence of the basin [5, 7, 9]. There are three coal seams in the basin: upper-KP1, lower-KM2, and middle-KM3.
Fig. 1. Map showing geological setting of Western Anatolia and location of coal fields [1]
Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
Fig. 2. Geological map of study area and generalized stratigraphic column section of study area [8]
2. Organic Facies Investigations KM2 lower coal seam which is one of the two coal seams in the Miocene Soma Formation has been investigated with respect to organic facies characteristics. About 90 hole samples were collected from 10 wells. Type of lithology and other sedimentary characteristics were considered for selection of samples to be analyzed. In order to determine the facies and nature of the organic matter, a number of organic petrographic and geochemical analyses were made upon the kerogen isolated from the hole samples. Total organic carbon (TOC), Rock Eval pyrolysis, vitrinite reflectance (Ro) and microscobic analyses were realized to determine the organic chemical characteristics of the Soma basin. TOC values were measured on 30 samples from the KM2 lower coal seam (Table 1). The results show that TOC values are between 28.45% and 73.38%, with an average around 56.61%. Hydrogen Index (HI) is between 11 and 28 mgHC/gTOC, with an average of 21.4 mgHC/gTOC. The Production index (PI) ranges from 0.01 to 0.05, with an average of 0.02 and Tmax ranges from 403oC to 429 0C, with an average of 420 0C. Organic geochemical measurements of samples were plotted on a hydrogen index-Tmax diagram (Fig. 3). The results show that the samples contain dominantly Type III kerogen.
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Table 1. Results of TOC and Rock-Eval analysis Well No
Depth TOC S1 S2 S3 Tmax HI OI PI S2/S3 OF 624.80 32.51 0.64 21.79 9.26 421 67 28 0.03 2 CD ES332 626.40 63.16 1.2 83.29 16.81 427 132 27 0.01 4 C 641.90 38.87 0.98 47.49 9.78 416 122 25 0.02 4 CD ES334 584.90 32.97 1.08 50.30 8.71 422 153 26 0.02 5 C 769.00 50.05 1.6 75.07 10.25 425 150 20 0.02 7 C ES338 771.10 65.21 1.18 108.17 10.48 416 166 16 0.01 10 C 776.20 39.36 1 56.64 8.03 429 144 20 0.02 7 C 842.20 66.98 0.24 44.88 15.18 429 67 23 0.01 2 CD 852.00 66.62 0.89 57.35 12.28 416 84 18 0.02 4 CD ES331A 846.90 67.42 1.19 109.53 10.79 412 162 16 0.01 10 C 857.00 64.23 2.5 86.66 10.36 403 135 16 0.03 8 C 666.50 65.69 0.81 77.85 15.88 415 119 24 0.01 4 CD ES342 671.10 70.23 7.78 160.51 7.67 389 229 11 0.05 20 C 673.80 67.16 1.04 63.85 17.7 422 95 26 0.02 3 CD 835.90 69.69 0.92 48.18 19.61 425 69 28 0.02 2 CD ES340 843.70 52.62 1.31 45.48 14.59 430 86 28 0.03 3 CD 850.00 58.52 0.98 51.81 12.17 417 89 21 0.02 4 CD 770.40 28.45 1.68 33.35 6.49 419 117 23 0.05 5 CD 774.65 71.02 0.99 69.54 13.79 422 98 19 0.01 5 CD ES344A 781.70 64.71 1.76 10.,94 9.50 414 168 15 0.02 11 C 790.40 44.36 1.04 109.12 6.43 413 246 14 0.01 16 C 764.00 58.61 1.2 90.42 6.56 419 154 11 0.01 13 C 774.65 62.92 0.69 60.46 11.14 421 96 18 0.01 5 CD ES349B 779.75 43.61 0.73 43.05 9.7 429 99 22 0.02 4 CD 788.80 29.74 0.93 54.60 6.36 428 184 21 0.02 8 C 1059.40 64.12 1.02 77.86 10.04 423 121 16 0.01 7 CD 1064.10 73.38 1.12 87.20 11.45 417 119 16 0.01 7 CD ES352 1069.50 72.66 2.52 113.53 8.14 396 156 11 0.02 13 C 1074.20 66.67 0.99 67.85 8.77 415 102 13 0.01 7 CD ES359 541.70 46.92 0.9 67.17 12.06 405 143 26 0.01 5 C TOC; Total Organic carbon (wt %). S1; Free Hydrocarbons in rock (mg HC\g rock). S2; Hydrocarbon generated from the thermal breakdown of kerogen (mg HC/g rock). S3; CO2 value (mg CO2\g rock). Tmax; Maximum temperature (oC). HI; Hydrogen Index (mg HC/g TOC). OI; Oxygen Index (mg CO2\g TOC). PI; Production Index (mg HC\g TOC). S2\S3; Hydrocarbon Type Index. PY; Potential Yield (mg HC\g TOC). OF; Organic Facies.
Organic petrographic analysis, including reflected white light examination of organic matter concentrates and polished section of whole rock was carried out using coal petrographic techniques [10]. Measurements of vitrinite reflectance were carried out to characterize thermal maturity of the organic matter. The results showed that the average value of vitrinite reflectance ranging from 0.35 to 0.48. Organic matter is composed predominantly of woody material. As a result of investigation, we were able to differentiate two organic facies types [11]. The two organic types were type C and CD. The geochemical variations are sufficient to differentiate organic facies types C and CD in the Soma Formation. Organic facies C and CD are related to clayey coal and coal lithofacies. Organic facies C is the 'gas-prone' facies. The organic matter is dominated by terrestrial debris in various stage of oxidizition. Volumetrically, organic facies CD is most typically deposited as a massive unit containing moderately to well oxidized terrestrial organic matter and substantial amounts of residual organic matter. It also occur in carbonate sequences where the algal organic matter has been highly oxidized.
Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
Fig. 3. HI-Tmax diagram of the investigated unit
3. Conclusions TOC contents (between 28.45% and 73.38%) in the selected samples show that the Miocene coals have enough organic matter indicating poor hydrocarbon source rock. HI values of KM2 seam are around 11 and 28 mgHC/gTOC showing mostly characteristic of Type III kerogen. Rock-Eval Tmax and PI values are about 420 0C and less than 0.05 respectively. Tmax, PI and Ro values show that the organic matter in the samples are immature in terms of organic maturation. Organic facies type C and CD were identified in the Soma Formation.
Acknowledgements This study was supported by the Research Unit of the Akdeniz University (Project Number: 2013.03.0121.004). The authors would like to thanks Turkish Petroleum Corporation (TPAO) (Turkey) and Turkish Coal Entreprises (TKI).
References [1] Yagmurlu F, Inaner H, Nakoman E, Inci U. Age, tectonic setting, and quality distribution of the Neogene lignite deposits of western Anatolia. Geol. Belg. 2004;7(3-4):251-258 [2] Brinkmann K, Feist R, Marr WU, Nickel E, Schlimm W, Walter HR. Geology of Soma Mountains (in Turkish). Bulletin of Directorate of Mineral Research and Exploration 1970;74:41-57 [3] Nebert K. Lignite bearing Soma Neogene area, western Turkey (in Turkish). Bulletin of Directorate of Mineral Research and Exploration. 1978;90:20-70 [4] Karayigit AI, Whateley MKG. Properties of lacustrine subbituminous coal seam (k1) from the Soma Basin and investigation of contact metamorphic influence on this seam, western Turkey. International Journal of Coal Geology 1997;34:131-155 [5] Karayigit AI. Thermal effects of a basaltic intrusion on the Soma lignite bed in West Turkey. Energy Sources 1998;20(1):55-66.
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[6] Inci U. Miocene Synvolcanic Alluvial Sedimentation in Lignite-bearing Soma Basin, Western Turkey. Journal of Earth Science 1998;63-78. [7] Inci U. Depositional evolution of coal successions in the Soma coalfield, western Turkey. International Journal of Coal Geology 2002;51:129. [8] Tan T, Erturk I, Pekmezci F, Altınay A. Manisa-Soma-Eynez İzmir-Kınık-Yaylaköy Sahası (in Turkish). TKI 2010;report no:21.01.2010. [9] Bulut Y, Karayigit AI. Petrography of feed coals in the Soma power plant, Manisa, Turkey. Energy Sources 2006;28:1447-1459. [10] Stach E, Mackowsky M-Th, Teichmuller M, Taylor GH, Chandra D, Teichmuller R. Stach’s Textbook of Coal Petrology, Gebrüder Borntraeger, Berlin 1982;535 p. [11] Jones RW. Organic Facies. In: Advances in Petroleum Geochemistry, Brooks, J. and Welte, D. (eds.), Academic Press, London 1987;2:1-90.
ScienceDirect Energy Procedia 76 (2015) 27 – 32
European Geosciences Union General Assembly 2015, EGU Division Energy, Resources & Environment, ERE
Organic facies characteristics of the Miocene Soma Formation (Lower Lignite Succession-KM2), Soma Coal Basin, western Turkey Selin Hokerek*, Orhan Ozcelik Department of Geological Engineering, Akdeniz University, Antalya,07058, Turkey
Abstract The Soma coal basin is one of the largest economic lignite-bearing alluvial basins of western Turkey. The Miocene succession of the coalfield contains two lignite seams successions; Lower Lignite, Middle Lignite. Kerogen in the deposits is type III, as indicated by organic petrographic observations and Rock-Eval data. Total organic carbon (TOC) values are between 28.45 and 73.38% in the formation. Tmax values vary between 403 and 429°C, confirming maturation trends indicated by vitrinite reflectance data (between 0.35-0.48 Ro%). Organic facies type C and CD were identified in the investigated units. The organic matter is partly oxidized/oxidized and reworked. © 2015 2015 The byby Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license © TheAuthors. Authors.Published Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the GFZ German Research Centre for Geosciences. Peer-review under responsibility of the GFZ German Research Centre for Geosciences
Keywords: Western Turkey; Bakırçay Graben; Soma Formation; organic facies; organic geochemistry
1. Introduction The study area is located within Western Anatolian extensional province (WAEP) characterized by numerous E– W grabens and NNE-trending basins. The lignite bearing sedimentary basins in Western Anatolia arose resulting
* Corresponding author. Tel.: +90-242-310-4307; fax: +90-242-310-6306. E-mail address: [email protected]
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the GFZ German Research Centre for Geosciences doi:10.1016/j.egypro.2015.07.836
28
Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
from intra-continental extensional tectonic regime developing in Miocene (Fig.1). These lignite basins are bound by growth faults and contain sedimentary and volcanic rock assemblages [1]. The geology of the Soma coal basin was described and illustrated in detail earlier [2, 3, 4, 5, 6, 7, 8]. A simplified geologic map southern Soma and generalized stratigraphic sequence of the Soma basin are depicted in Fig. 2. The Soma and Denis Formations, which were characterized by nonmarine, laterally extensive, and lacustrine units dominated by limestone, marl, and claystone, form the sedimentary sequence of the basin [5, 7, 9]. There are three coal seams in the basin: upper-KP1, lower-KM2, and middle-KM3.
Fig. 1. Map showing geological setting of Western Anatolia and location of coal fields [1]
Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
Fig. 2. Geological map of study area and generalized stratigraphic column section of study area [8]
2. Organic Facies Investigations KM2 lower coal seam which is one of the two coal seams in the Miocene Soma Formation has been investigated with respect to organic facies characteristics. About 90 hole samples were collected from 10 wells. Type of lithology and other sedimentary characteristics were considered for selection of samples to be analyzed. In order to determine the facies and nature of the organic matter, a number of organic petrographic and geochemical analyses were made upon the kerogen isolated from the hole samples. Total organic carbon (TOC), Rock Eval pyrolysis, vitrinite reflectance (Ro) and microscobic analyses were realized to determine the organic chemical characteristics of the Soma basin. TOC values were measured on 30 samples from the KM2 lower coal seam (Table 1). The results show that TOC values are between 28.45% and 73.38%, with an average around 56.61%. Hydrogen Index (HI) is between 11 and 28 mgHC/gTOC, with an average of 21.4 mgHC/gTOC. The Production index (PI) ranges from 0.01 to 0.05, with an average of 0.02 and Tmax ranges from 403oC to 429 0C, with an average of 420 0C. Organic geochemical measurements of samples were plotted on a hydrogen index-Tmax diagram (Fig. 3). The results show that the samples contain dominantly Type III kerogen.
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Table 1. Results of TOC and Rock-Eval analysis Well No
Depth TOC S1 S2 S3 Tmax HI OI PI S2/S3 OF 624.80 32.51 0.64 21.79 9.26 421 67 28 0.03 2 CD ES332 626.40 63.16 1.2 83.29 16.81 427 132 27 0.01 4 C 641.90 38.87 0.98 47.49 9.78 416 122 25 0.02 4 CD ES334 584.90 32.97 1.08 50.30 8.71 422 153 26 0.02 5 C 769.00 50.05 1.6 75.07 10.25 425 150 20 0.02 7 C ES338 771.10 65.21 1.18 108.17 10.48 416 166 16 0.01 10 C 776.20 39.36 1 56.64 8.03 429 144 20 0.02 7 C 842.20 66.98 0.24 44.88 15.18 429 67 23 0.01 2 CD 852.00 66.62 0.89 57.35 12.28 416 84 18 0.02 4 CD ES331A 846.90 67.42 1.19 109.53 10.79 412 162 16 0.01 10 C 857.00 64.23 2.5 86.66 10.36 403 135 16 0.03 8 C 666.50 65.69 0.81 77.85 15.88 415 119 24 0.01 4 CD ES342 671.10 70.23 7.78 160.51 7.67 389 229 11 0.05 20 C 673.80 67.16 1.04 63.85 17.7 422 95 26 0.02 3 CD 835.90 69.69 0.92 48.18 19.61 425 69 28 0.02 2 CD ES340 843.70 52.62 1.31 45.48 14.59 430 86 28 0.03 3 CD 850.00 58.52 0.98 51.81 12.17 417 89 21 0.02 4 CD 770.40 28.45 1.68 33.35 6.49 419 117 23 0.05 5 CD 774.65 71.02 0.99 69.54 13.79 422 98 19 0.01 5 CD ES344A 781.70 64.71 1.76 10.,94 9.50 414 168 15 0.02 11 C 790.40 44.36 1.04 109.12 6.43 413 246 14 0.01 16 C 764.00 58.61 1.2 90.42 6.56 419 154 11 0.01 13 C 774.65 62.92 0.69 60.46 11.14 421 96 18 0.01 5 CD ES349B 779.75 43.61 0.73 43.05 9.7 429 99 22 0.02 4 CD 788.80 29.74 0.93 54.60 6.36 428 184 21 0.02 8 C 1059.40 64.12 1.02 77.86 10.04 423 121 16 0.01 7 CD 1064.10 73.38 1.12 87.20 11.45 417 119 16 0.01 7 CD ES352 1069.50 72.66 2.52 113.53 8.14 396 156 11 0.02 13 C 1074.20 66.67 0.99 67.85 8.77 415 102 13 0.01 7 CD ES359 541.70 46.92 0.9 67.17 12.06 405 143 26 0.01 5 C TOC; Total Organic carbon (wt %). S1; Free Hydrocarbons in rock (mg HC\g rock). S2; Hydrocarbon generated from the thermal breakdown of kerogen (mg HC/g rock). S3; CO2 value (mg CO2\g rock). Tmax; Maximum temperature (oC). HI; Hydrogen Index (mg HC/g TOC). OI; Oxygen Index (mg CO2\g TOC). PI; Production Index (mg HC\g TOC). S2\S3; Hydrocarbon Type Index. PY; Potential Yield (mg HC\g TOC). OF; Organic Facies.
Organic petrographic analysis, including reflected white light examination of organic matter concentrates and polished section of whole rock was carried out using coal petrographic techniques [10]. Measurements of vitrinite reflectance were carried out to characterize thermal maturity of the organic matter. The results showed that the average value of vitrinite reflectance ranging from 0.35 to 0.48. Organic matter is composed predominantly of woody material. As a result of investigation, we were able to differentiate two organic facies types [11]. The two organic types were type C and CD. The geochemical variations are sufficient to differentiate organic facies types C and CD in the Soma Formation. Organic facies C and CD are related to clayey coal and coal lithofacies. Organic facies C is the 'gas-prone' facies. The organic matter is dominated by terrestrial debris in various stage of oxidizition. Volumetrically, organic facies CD is most typically deposited as a massive unit containing moderately to well oxidized terrestrial organic matter and substantial amounts of residual organic matter. It also occur in carbonate sequences where the algal organic matter has been highly oxidized.
Selin Hokerek and Orhan Ozcelik / Energy Procedia 76 (2015) 27 – 32
Fig. 3. HI-Tmax diagram of the investigated unit
3. Conclusions TOC contents (between 28.45% and 73.38%) in the selected samples show that the Miocene coals have enough organic matter indicating poor hydrocarbon source rock. HI values of KM2 seam are around 11 and 28 mgHC/gTOC showing mostly characteristic of Type III kerogen. Rock-Eval Tmax and PI values are about 420 0C and less than 0.05 respectively. Tmax, PI and Ro values show that the organic matter in the samples are immature in terms of organic maturation. Organic facies type C and CD were identified in the Soma Formation.
Acknowledgements This study was supported by the Research Unit of the Akdeniz University (Project Number: 2013.03.0121.004). The authors would like to thanks Turkish Petroleum Corporation (TPAO) (Turkey) and Turkish Coal Entreprises (TKI).
References [1] Yagmurlu F, Inaner H, Nakoman E, Inci U. Age, tectonic setting, and quality distribution of the Neogene lignite deposits of western Anatolia. Geol. Belg. 2004;7(3-4):251-258 [2] Brinkmann K, Feist R, Marr WU, Nickel E, Schlimm W, Walter HR. Geology of Soma Mountains (in Turkish). Bulletin of Directorate of Mineral Research and Exploration 1970;74:41-57 [3] Nebert K. Lignite bearing Soma Neogene area, western Turkey (in Turkish). Bulletin of Directorate of Mineral Research and Exploration. 1978;90:20-70 [4] Karayigit AI, Whateley MKG. Properties of lacustrine subbituminous coal seam (k1) from the Soma Basin and investigation of contact metamorphic influence on this seam, western Turkey. International Journal of Coal Geology 1997;34:131-155 [5] Karayigit AI. Thermal effects of a basaltic intrusion on the Soma lignite bed in West Turkey. Energy Sources 1998;20(1):55-66.
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[6] Inci U. Miocene Synvolcanic Alluvial Sedimentation in Lignite-bearing Soma Basin, Western Turkey. Journal of Earth Science 1998;63-78. [7] Inci U. Depositional evolution of coal successions in the Soma coalfield, western Turkey. International Journal of Coal Geology 2002;51:129. [8] Tan T, Erturk I, Pekmezci F, Altınay A. Manisa-Soma-Eynez İzmir-Kınık-Yaylaköy Sahası (in Turkish). TKI 2010;report no:21.01.2010. [9] Bulut Y, Karayigit AI. Petrography of feed coals in the Soma power plant, Manisa, Turkey. Energy Sources 2006;28:1447-1459. [10] Stach E, Mackowsky M-Th, Teichmuller M, Taylor GH, Chandra D, Teichmuller R. Stach’s Textbook of Coal Petrology, Gebrüder Borntraeger, Berlin 1982;535 p. [11] Jones RW. Organic Facies. In: Advances in Petroleum Geochemistry, Brooks, J. and Welte, D. (eds.), Academic Press, London 1987;2:1-90.