Stratigraphic Trap Exploration in a Mature Basin:Examples for New Concepts from the Austrian Molasse Basin

摘要

In the Molasse foreland basin of Upper Austria gas is produced from deep-water sandstones and conglomerates of the Puchkirchen and basal Hall formations (Oligocene-Lower Miocene).The basin is mature,with >750 wells drilled by RAG to date.An extensive 3-D seismic reflection dataset that covers much of the paleo-basin foredeep has been acquired in the study area over the last 15 years.Seismic strati-graphic analysis has revealed that deep-water sedimentation in the basin was dominated by a channel belt up to 5 km wide that transported sediment derived from the Central and Eastern Alps eastward along the basin axis [11,12].Based on these findings,a detailed sedimentary fades model has been developed,outlining several distinct depositional elements that reveal numerous possible stratigraphic trap types (de Ruig and Hubbard,2006).This depositional model is currently being applied and tested in exploration and refined by ongoing research.Channel abandonment and migration are important processes that resulted in strati-graphic configurations consisting of Coarse-grained sandstones and conglomerates overlain by channel and overbank mudstones (Hubbard et al,in press).This represents ideal reservoir architecture,including porous reservoir fades sealed by impermeable deposits.Additional strati-graphic trapping conditions can result from special spatial arrangements of depositional elements,for example a sandstone-filled tributary channel that is sealed by an overlying mudstone-filled abandonment channel.Recognizing and further improving such stratigraphic trapping configurations are important for future exploration in Upper Austria,where most of the structural traps have been drilled.