Triassic of the Barents Sea shelf: depositional environments and hydrocarbon potential Daria A. Norina1,2 1TOTAL (Paris, France) 2The work is a part of PhD thesis conducted in Petroleum Department, Geological faculty of Lomonosov MSU (Moscow, Russia) FORCE workshop “Triassic and Jurassic reservoir development in the Barents Sea”, 9-10 June 2015 Presented evaluation of structure, depositional environments, cyclicity and hydrocarbon potential of Triassic complex in the Barents Sea shelf is based on interpretation of 2D seismic lines, well log data for 17 wells, descriptions of well sections and outcrops, source rock geochemical analysis and 2D basin modeling. Triassic clastic complex reaches the maximum thickness of 10.5-12 km within the South Barents basin and pre-Novaya Zemlya foredeep. Its lower boundary is represented by Permian- Triassic erosion unconformity in the south-eastern margin of the basin and marked by the downlap of Induan clinoforms. Upper boundary corresponds to the Rhaetian erosion unconformity best pronounced in the pre-Novaya Zemlya foredeep, Kola monocline and Pechora Sea. Interpreted Triassic reflectors – top Induan, top Olenekian, top Ladinian – are correlated with sequence boundaries in wells. Triassic sediments of the Barents Sea were deposited in deltaic, shallow-marine to deep shelf environments in the large epicontinental basin. Up to 8 transgressive-regressive sequences were identified in the well sections of the Eastern Barents Sea. Deltaic sediments coming from the main south-eastern (Timan-Pechora) and eastern (Novaya Zemlya and Kara land) provenances compensated the steady subsidence of the South- and North Barents basins and pre-Novaya Zemlya foredeep in Early and Middle Triassic. Progradation of Induan clinoforms is well-traced across the South-Barents basin towards the area of non-compensated deep shelf deposition in the west and north-west. Since Olenekian the clinoform break persisted in the western shelf; no clinoforms are observed in the Eastern Barents shelf where deltaic environments had prevailed. Periodic marine transgressions led to significant lateral shift of the shoreline: the delta plain was flooded and more shaly packages were deposited forming transgressive system tracts. In the Late Triassic the non- compensated area in the north-west was progressively filled with sediments. Cyclicity of Triassic section controls the alternation of marine shales containing a mix of marine and terrestrial organic matter (type II-III) and deltaic sediments with type III of organic matter. The proportion of marine organic matter (type II) as well as total organic matter content increases towards the west and north-west of the Barents Sea shelf where Lower and Middle Triassic source rocks have high oil and gas generation potential. Triassic source rocks in the Eastern Barents shelf contain predominantly type III of organic matter and have variable gas generation potential, except for the shales deposited during marine transgressions and capable of liquid hydrocarbons generation. Main Triassic source rock kitchens are situated within the South and North Barents basins, Saint Anna through and basins within the Western Barents shelf. Prospective zones of gas accumulation are related to these basins, where Triassic source rocks have high maturity. Zone of possible oil accumulations is situated in the north-west of the shelf. Zones of oil-gas accumulations are predicted on the basins margins and within the saddles. Fig. 1. Triassic seismostratigraphic complex of the Eastern Barents Sea shelf on seismic data and Triassic transgressive-regressive sequences in wells with results of source rock analysis FORCE seminar “Triassic and Jurassic reservoir development in the Barents Sea” Daria A. NORINA TOTAL (Paris, France) The work was conducted in Petroleum Department, Geological faculty of Lomonosov MSU (Moscow, Russia) Stavanger, 9-10 June 2015 Fields in Triassic reservoirs Oil fields – Goliath Gas-condensate fields - Peschanoozerskoe Gas fields – Murmanskoe, Severo-Kildinskoe 2D regional seismic (MAGE) – 12000 km, 10-12 s Well logs - 17 wells (MAGE, NPD) Outcrop and well section descriptions – 17 (biblio, reports) 20 samples from outcrops – Franz Josef Land, Svalbard (VSEGEI, MGU) Legend geochemical data (biblio) Geochemical data for 150 samples outcrop samples outcrop sections well logs and sections for Russian wells (MGU, VSEGEI, AMNGR) and Norwegian wells (NPD) Extensional Paleozoic Fold belts: depressions Baikalian , 2011 Relatively stable areas of the Caledonian Stoupakova ancient platforms Hercynian Syneclise Cimmerian Monocline Inverted swells Shoreline Depressions, extensional basins Seismic lines Domes and basement uplifts Study of structure, thickness, Identification of source 1 cyclicity, depositional 2 rock intervals environments Seismostratigraphic MFS identification Rock description Pyrolysis interpretation (seismic, logs) (macro, micro) Rock-Eval Luminescent test Extraction in Well log interpretation Paleogeographic of extracts organic solvent and correlation, sequence sketches (seismic, well stratigraphy analysis logs and sections, outcrops ) Gas Gas chromatography Chromatography Mass-spectrometry Identification of vertical and lateral variation of initial Triassic source rock 3 properties and hydrocarbon generation potential Reconstruction of HC generation Identification of present day oil 4 5 and migration processes and gas generation kitchens 2D basin modeling Ro Tmax (Temis Flow) NW SE Permian-Triassic unconformity A BJU Top of Permian 6s carbonates T P A Ia 730 km BJU –Rhaetian erosional unconformity Widespread in the basin Thickness up to 8-10 km Upper and lower boundaries are represented by regional unconformities S-Kildinskaya 82 Murmanskaya-24 Upper Triassic sub-complex Middle Triassic sub-complex Olenekian sub-complex А1’ А1 Induan sub-complex Horizon А1 – Induan/Olenekian boundary Horizon A2 – Lower/Middle Triassic boundary Horizon А3 – Middle / Upper Triassic boundary A1 5 A’ A 5 Model of clinoform progradation (Glorstad-Clark, 2010) 4 3 2 1 W E A ’ 1 0.6 km 3 km 3.6 km W SE ’ ’ A1 A1 540 m A ’ 1 785 m A 1.2 km 1 1.5 km 1.9 km А – top Рermian А1 – Induan/Olenekian >2 km А1’ – Lower/Upper Olenekian Transgressive cycle A2 – Lower/Middle Triassic Regressive cycle Shaly sandstone with coal lenses Fresmanovskaya-1, T1o Central Nagurskaya Svalbard (FJL) Hopen-2 Eastern Svalbard 100 m Bjornoya 500 m 150 m 600 m Progradation of clinoform break 30 m W SE 190 м 285 m Transgressive cycle 403 m Regressive cycle 441 m 425 m 640 m NW SE ’ 6s A1 A1 730 km Clinoforms are not observed on seismic in the Eastern Barents sector in Mid Triassic Less thick than Lower Triassic Marine transgression and corresponding transgressive tracts SW NE Middle Triassic thickness increase towards Novaya Zemlya ’ Middle Triassic thickness A1 A1 decrease on Admiraltey high (Krestovaya well) E W А3 350 m 810 m 705 m А2 Anisian age Ladinian age 2 1 2 1 Glorstad-Clark, 2010 NW SE A’ A Central Nagurskaya Svalbard (FJL) Eastern Svalbard Hopen-2 250 m 50 m 680 m 300 m Severnaya Bjornoya 50 m 1.6 km W SE N 200 m Transgressive cycle Regressive cycle 840 m No clinoforms observed in Eastern Barents Early and Late Carnian transgressions – shaly units Less thick than Lower & Middle Triassic SW NE Hopen-2 Eastern Svalbard Severnaya Clinoform break (Glorstad-Clark, 2010) 950 m Bjornoya 100 m 2 km Organic matter type Total organic carbon distribution, % Distribution of steranes С27, С28, С29 Ph/n-C18 vs Pr/n-C17 Alkane distribution (GC) isoprenoids n-alkanes to Organic matter type T2a - Svalbard Total organic carbon distribution, % х10 Distribution of steranes С27, С28, С29 Ph/n-C18 vs Pr/n-C17 Alkane distribution (GC) Alkane distribution (GC) isoprenoids init. init. n-alkanes init. init. to to Organic matter type Total organic carbon distribution, % Distribution of steranes С27, С28, С29 Ph/n-C18 vs Pr/n-C17 Alkane distribution (GC) isoprenoids n-alkanes to to to Line A Source rocks Line B Source rocks - Calculated Ro 2 profiles across South-Barents basin - Measured Ro calibration with Ro (%) data for 7 wells Top of oil window – 2,2-3 km, top of gas window – 4,2-4,9 km, base of gas window – 5,5-7 km Induan SR started to generate HCs at the end of Early Triassic no present day generation Olenekian, Middle Triassic and partly Upper Triassic SRs form present day hydrocarbon generation kitchens Line B Maturity was estimated using: Т1 Tmax – Rock Eval pyrolysis Ro (%) – vitrinite reflectance Results of basin modeling for South Barents basin Hydrocarbon generation kitchens: South-Barents basin North-Barents basin Basins on Norwegian shelf (Nordkapp, Hammerfest… ) St. Anna through Т2 Т3 4 perspective zones with different fluid type are identified: oil accumulation zone gas-oil accumulation zone (mostly oil) oil-gas accumulation zone (mostly gas) gas accumulation zone Triassic seismostratigraphic complex has a progradational character. Deltaic sediments coming from the south-eastern (Timan-Pechora) and eastern (Kara land) provenances compensated the subsidence of the South- and North Barents basins and pre-Novaya Zemlya foredeep in Early-Middle Triassic: maximum thicknesses are mapped During marine regressions deltaic plain prograded to the west and north-west feeding the deep shelf area with sediments. During marine transgression deltaic plain was flooded, and the shoreline moved landwards. Depositional cyclicity has resulted in the presence of up to 8 transgressive- regressive Triassic sequences in the well sections of the Eastern Barents Sea. Transgressive marine shales contain a mix of marine and terrestrial organic matter (type II-III) and regressive deltaic sediments - type III of organic matter. The proportion of marine organic matter (type II) and TOC content of Lower and Middle Triassic source rocks increases towards the west and north-west of the Barents Sea determining high oil and gas generation potential of the area. Triassic gas kitchens are situated within the South and North Barents basins, St.Anna through and western Barents basins. Zone of possible oil accumulations is situated in the north-west of the shelf. Thank you for attention! .