Modelling of seismic reflection data for underground gas storage in the Pečarovci and Dankovci structures - Mura Depression

Abstract

Two antiform structures in the Mura Depression were selected as the most promising in Slovenia for the construction of an underground gas storage facility in an aquifer. Seventeen reflection lines with a total length of 157km were recorded, and three boreholes were drilled. Structural models corresponding to two different horizons (the pre-Tertiary basement and the Badenian-Sarmatian boundary) were constructed using the Sierra Mimic program. Evaluation of different velocity data (velocity analysis, sonic log, the down-hole method, and laboratory measurements on cores) was carried out in order to perform correct time-to-depth conversion and to establish lateral velocity variations. The porous rock in Pečarovci structure is 70m thick layer of dolomite, occurring at a depth of 1900m, whereas layers of marl, several hundred meter thick, represent the impermeable cap-rock. Due to faults, the Dankovci structure, at a depth of 1200m, where the reservoir rocks consist of thin layers of conglomerate and sandstone, was proved to be less reliable. ID synthetic seismograms were used to correlate the geological and seismic data at the borehole locations, especially at intervals with thin layers. The raytracing method on 2D models (the Sierra Quik package) was applied to confirm lateral continuity of some horizons and to improve the interpretation of faults which are the critical factor for gas storage.