Abstract: Improved concepts with first results for the imbricated molasse and triangle - zone in Austria based on 3D seismic

WAGINI, ALEXANDER

The first well drilled through the imbricates of the Upper Austrian Molasse-zone was Perwang 1 in the year 1958. The imbricates were not recognized as such before the well was drilled, but a 6-fold repetition of the Eocene changed the tectonic concept. Over the years, some more wells penetrated the imbricates in search for deeper targets, until in 1987 Berndorf 1 found commercial gas in a Puchkirchen Formation imbricate. In 1989 Muhlreith 1 followed with the first oil discovery in a Rupelian imbricate making the imbrictes more attractive and an object for more intensive investigations.

Not until the imbricates were covered by 3D seismic, a detailed analysis of the complex structure of the imbricates and especially the triangle zone became possible. The concurrence of different ray paths for neighboring seismic traces, very steeply dipping layers and extensive faulting in an area of limited geologic knowledge represents a real challenge. The transfer of models from the Canadian Rocky Mountains, the integration of the results of theoretical and plaster models together with local knowledge resulted in the concept for the triangle-zone well Strassrwalchen 1. The drilling-results of Strassrwalchen 1 verified this concept; however, all tested gas layers have turned out not to be commercial as yet. FMI-logs show a certain influence of the high tectonic stress on the reservoir, but high flow rates and good permeabilities counter the effect. A further, more-in-depth analysis of the seismic revealed additional subtle detachment surfaces that could have compartmentalized the reservoirs.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria