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Structural-tectonic interpretation of Stružec gas and oil field

The Stružec field is located at the northwestern, deep part of the Sava depression, along the southwestern margin of the Pannonian basin. Interpretation of three-dimensional seismic data on the Stružec field has been done using the Petrel software package. Interpretation has included mapping of characteristic horizons. Types of faults were determined according to the relative movement of the hanging wall with regard to the footwall. This way, the faults were interpreted as reverse and normal. Reverse faults interpreted in the area of Stružec anticline are generally oriented in the east-west direction, while normal faults are nearly perpendicular to them, extending in the north-south direction (Šumanovac, 2012). The basic structure observed at the Stružec oil and gas field is an elongated anticline, i.e. brachyanticline extended in the east-west direction. The anticline is bounded by two main reverse faults, and is faulted by a series of transverse normal faults. Other faults extending approximately parallel to the main reverse faults. Geodynamic evolution of the Pannonian basin has been described in many papers and has been commonly considered in relation to the Alpine and Carpathian orogeny (Tari & Pamić, 1998). The main extensional phase in the southwestern part of the Pannonian Basin ends between Sarmatian and Pontian. The extension ended during the Pontian, and during the Pliocene orientation of stress changed with the development of compressional forces. Transect through the Sava Suture Zone (Ustaszewski et al., 2010) depicts inversion of numerous normal faults after the Pontian, showing tilted and deformed Pontian sediments. That is in agreement with earlier work in adjacent parts of the Pannonian Basin suggesting compressional and/or transpressional reactivation of extensional faults (Tari & Pamić, 1998). Compressional stress is still going on, which causes the formation of flower structures and anticlines (Horvath, 2006). Structure formation in the Stružec field can be considered in two basic approaches. The first one defines two tectonic phases. First phase begins in the Pliocene where compressional forces cause reverse faulting and anticline forms by deformation of the hanging wall. Seismic amplitude and attribute sections show positions of the main reverse faults, which caused the formation of Stružec anticline. In the second phase, normal faulting of the anticline is caused by extension. The second approach considers only one phase. That is parallel formation of reverse and normal faults. The compression causes formation of reverse faults and strong deformations of the hanging wall with development of a steep anticline. At the same time at the crest of the anticline normal faults are formed under stress relief.

Interpretation of 3-D seismic data ; Pannonian Basin

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