GEOCHEMISTRY OF OIL AND SOURCE ROCKS AND PETROLEUM POTENTIAL OF THE WESTERN PART OF THE BALTIC SYNECLISE Zdanaviciute, O., Dakhnova, M. V.

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1 GEOCHEMISTRY OF OIL AND SOURCE ROCKS AND PETROLEUM POTENTIAL OF THE WESTERN PART OF THE BALTIC SYNECLISE Zdanaviciute, O., Dakhnova, M. V., Zheglova,T. P.

2 Content of the talk Geological framework Data and methods Stratigraphic distribution and thickness of potential source rocks Organic richness, kerogen composition and thermal maturity Crude Oils composition Hydrocarbon generation, migration and entrapment in the eastern part of the Baltic Syneclise

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4 The structural map of the top of the Cambrian Compiled by Dadlez, R., Kanev, S., Modlinski, Z., Sakalauskas, K., Zdanavičiūtė, O. (Zdanavičiūtė et al, 1999) LEGEND 1 contour lines of the top of the Cambrian; 2 faults; 3 bounda-ries of the distribution of Cambrian deposits; 4 the folds without Cambrian deposits; 5 oil fields; 6 gas condensate fields; 7 oil in the boreholes.

5 Stratigraphic distribution and thickness of potential source rocks

6 The scheme of organic matter distribution in the Middle Cambrian and Ordovician (a) argillites and siltstones and in the Silurian dark-grey argillaceous complex (b). Modified after Kadūnienė et al. (2001)

7 Cross-plots of Rock-Eval S2 vs. TOC (a) and Hydrogen Index vs. Tmax (b)

8 Representative chromatograms shoving the alkane distribution in the oils from the Precambrian, Cambrian, Ordovician, Silurian and Devonian reservoirs The data of oil composition Well, (age) Density o API, Aliph. Arom. Polars Prist /Phyt CPI* Kulikovsk-1; (D) Bebirva-111; (S) Gusev-6; (O) Ablinga-2; (Cm) D5-1; (Cm) Girkaliai-2; (PreCm) * CPI Carbon Preference Index calculated for the n-c range;

9 Triangular plot of C27, C28, C29 regular sterane composition (left) and plot of regular sterane parameters C29 20S/(20S+20R) versus C29 ßß/(ßß+αα) (right)

10 3D models of oil migration and accumulation of the southwestern part of the Baltic Syneclise. a) b) Oil flow 70 to 00 Ma Oil flow 70 to 00 Ma The map of modeled oil flow (mill. Scum/sqm/My)for the 70-0 My plot: intensity of the oil flow indicated in colors (scale in the right side of the plot); a) regional faults are in red; histograms show the entrapped volume of hydrocarbons at 0 My: free capacity of the trap is shown in blue, entrapped oil - in green, gas solution - in yellow; free gas -in red; b) black blocky lines indicate contours of the traps; oil migration paths are shown in orange

11 Conclusions The organic matter of the source rocks can be attributed to the oilprone sapropel type, related to the sediments of the marine origin. Kerogen maturity varies from immature in the northeastern part of the Baltic Syneclise to the mature, peak oil window and post mature towards the Teisseyre Tornquist zone. A crude oil density, viscosity, asphaltene and resin content decreases with depth. Gas chromatograms of the alkanes are unmodal, dominated by C13 C19 homologs (with a peak maxima at C15), and decreases considerably in the range where the number of hydrocarbon atoms exceeds C20. Oils of the Baltic Syneclise are characterised by a very low concentration of sterane and triterpane biomarkers. The oil generation in the Baltic Syneclise started at the end of the Silurian, the major oil generation phase is thought to occur during the Devonian and Permian times. The oilfields formed during a long geological time and were recurrently recharged by the new oil from the Ordovician and Silurian source rock complexes.

12 Thank you very much for your attention The photo of exploitation site of well Pietų Šiūpariai-5