A.N. Gavrilov, E.V. Astaf'ev, G.V. Shakirova, Yu.I. Nikitin, N.N. Koryagin
 
Reducing the velocity anomalies effect on the accuracy of structural imaging: method of layer substitution in the stage of 3D seismic data interpretation
DOI 10.31087/0016-7894-2019-6-57-66

This paper discusses a methodology that allows minimizing the effect of velocity anomalies associated with lithological inhomogeneity of Kungurian halogenic-sulfate sequence of the Permian interval on structural imaging based on seismic data. These formations are widely occurring within the Volga-Urals Petroleum Province; their thickness increases considerably towards the south – to the Caspian Syneclise. The effect of velocity anomalies on seismic wavefield responds to the difference in acoustic properties of the rocks, which compose these intervals, namely, rock salt and anhydrite pinching out and replacing each other in lateral direction. Resulting from variations of total thickness of certain formations or their proportion, interval velocity of seismic waves propagation is respectively decreases of increases, as well as their traveltime in the rock formations. As a result, the wavefield becomes distorted and seismic artefacts occur below the zones of the reduced total thickness of salt, where sulfate component prevails in the section; high interval velocities are typical of these areas. As for the zones of increased salt thickness having lower density and therefore lower interval velocities, the underlying horizons are “forced through” thus forming the false troughs and smoothing the real structures. The authors made an effort to quantify the impact of these anomalies on structural position of underlying reflectors and, respectively, to determine structural geometry taking into account minimization of the distorting effect of velocity anomalies. This methodology was further developed in the Orenburgneft areas confined to the shoulder system of the Mukhanovo-Erkhovsky Trough (Kamsky-Kinel’sky system of troughs); high exploration maturity with 3D seismic and intensive deep drilling is typical of this area. Despite the long history of exploration activities in the Orenburg Oblast and the large amount of the explored reserves, application of new methodological approaches in seismic data interpretation allows discovering new fields annually.

Key words: halogenic-sulfate sequence; velocity anomalies; disconfirmation of structural geometry; 3D seismics; method of layer substitution; minimization of distorting influence; prospecting drilling; exploration; Volga-Urals Petroleum Basin.

For citation: Gavrilov A.N., Astaf'ev E.V., Shakirova G.V., Nikitin Yu.I., Koryagin N.N. Reducing the velocity anomalies effect on the accuracy of structural imaging: method of layer substitution in the stage of 3D seismic data interpretation. Geologiya nefti i gaza. 2019;(6):57–66. DOI: 10.31087/0016-7894-2019-6-57-66.

References

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A.N. Gavrilov

LLC TNNC, Tyumen', Russia;

ANGavrilov@tnnc.rosneft.ru

E.V. Astaf'ev

LLC TNNC, Tyumen', Russia;

EVAstafyev@tnnc.rosneft.ru

G.V. Shakirova

LLC TNNC, Tyumen', Russia;

GVShakirova@tnnc.rosneft.ru

Yu.I. Nikitin

LLC TNNC, Tyumen', Russia;

YINikitin@tnnc.rosneft.ru

N.N. Koryagin

AO «Orenburgneft'», Buzluk, Russia;

NNKoryagin@rosneft.ru