Seismic reflection synthetics and petrophysical properties.

Effective mapping of Parfenovo horizon top through seismic reflection data interpretation is due to dramatic difference between seismic P-wave velocities in terrigenous Parfenovo horizon and overlying carbonate Katanga formation. At this geological boundary P-wave velocity may increase from 4600 to 6500-7000 m/sec. The entire upper part of Vendian terrigenous complex is reflected on seismic time sections as a single composite wave (wavetrain M), mainly contributed by reflections generated on the Parfenovo horizon top and bottom as it is observed at Kovykta field. Earlier it was shown that at this area the averaged porosity values of Parfenovo horizon sandstones (either only P2 or both P1 and P2 units) have strong linear relationship with averaged wave-traveling time [3].

Within the area of Angara-Lensk and Levoberezhnoe fields the velocity differences between sandstones and underlying mudstones almost disappear. As a result, the main contribution in summary amplitudes of wavetrain M is made by the reflector at the top of Parfenovo sandstones. It was also concluded that some increase of amplitudes and time thicknesses of wavetrain M in Angara-Lensk field wells is due to thin layers (7-10 m) of sandstone characterized by relatively lower P-wave velocities than overlying and underlying deposits.

Fig. Crossplots of averaged porosity coefficient vs. averaged P-wave traveling time from wells of Angara-Lensk field (A) and from all wells of the studying area (B).

During this study the petrophysical parameter database was created using core data of A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS core collection. This database was used to make thick-layered and thin-layered models accordingly to the velocity models of wells. Figure displays crossplots of averaged porosity coefficient vs. averaged P-wave traveling time from wells of Angara-Lensk field (A) and from all wells of the studying area (B). Crossplotss analysis provided the conclusion that in Angara-Lensk field wells where lower-velocity layers are presented in the section there is stronger correlation of sandstone porosity values and its wave-traveling time.

Conclusion

Results of this study prove the conclusion that using prognosation criteria of Kovykta field for other perspective territories is not rightful enough. The strongest correlation of porosity and wave-traveling time is observed within the area nearest to the Kovykta field where the total thickness of Parfenovo horizon sandstones is up to 50-60 m. It is likely to be concerned with facies distribution. The thickness of sandstones of less than 30 m is a serious problem for 2D seismic survey that requires for futher investigations.

References

1. Khabarov Е.М., Varaksina I.V., Krotova М.М. et al. Lithologic-petrophysical characteristics of the Vendian Parfenovskiy horizon of the central part of Angara-Lena step // Collection of materials of V International scientific congress «GEO-Siberia-2009». – 2009. – P. 103-107. (in Russian)

2. Sovetov Y.K. The Upper Precembrian sandstones of south-western Siberian Platform. Novosibirsk: Nauka. - 1977. - 228 p. (in Russian)

3. Skuzovatov M.Y. Integrating of well-log, seismic and petrophysical data for prognosing reservoir properties of Parfenovo horizon of Kovykta field // Materials of all-Russian scientific conference with foreign scientists participation «Trofimuk readings of young scientists - 2011». - 2011. – P. 285-286. (in Russian)

Structural characteristic and tectonic evolution analysis of West Siberian basin northern areas in the Mesozoic and the Cenozoic (by results of regional seismic profiles 27 and 32 interpretation)

Surikova E.

A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia

[e-mail]

West Siberia is the largest gas-bearing province of the world. There are such unique gas giants, as Urengoi, Yamburg, Polar, Medvezhii, Bovanenkovo, Harasavei and other fields in this region. The main gas resources of this region are concentrated in apt-alb-senomanian unit and are controlled by high-peak anticlinal structures. The region is also rich with oil resources. Large oil pools are discovered on Southern Russian, Bovanenkovo, Urengoi, Vankor and other fields.

In spite of the fact that many hydrocarbon fields of the North of West Siberia are opened nearly half a century back questions of their formation still remain debatable. It concerns both genesis of hydrocarbons, and formation conditions of huge traps. This paper is about structural and tectonic aspects of this problem including creation of seismogeological model, studying of tectonic evolution of the region and establishment of large anticlinal structures – traps formation time in northern areas of the West Siberian petroleum province.

The basis of work was sublatitudinal No 27, 32 and submeridional No 109, 105 regional time sections of common depth point method and data of deep drilling of 70 wells located near lines of seismic sections. The pro section file No. 27 intersects Medvezhii, Urengoi, Russian and other fields. The section extent is 760 km. The section No. 32 located in 160 km to the North from a section No. 27, passes from Yamburg area in the West to the Yenisei folded belt in the east, crossing Yamburg, Yurkharovskii, Pyakyakhinskii and Vankor fields. The section extent is 440 km.

The interpretation of seismic data including stratification and correlation of the reflecting horizons, creation of depth seismogeological sections and paleosections was realized using W-Seis software developed in IPGG.

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