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Matzen Field Redevelopment, Pitfalls and Ways to Improve

Abstract

The giant Matzen Field is located 30 km north-east of Vienna, Austria. The multi-pool oil and gas field was discovered in 1949 and is the largest in the Vienna Basin. The structure is a shallow anticline with an axis in the ENE-WSW direction and an extension of 12×5 km. It is bounded to the North and West by a system of normal faults and delimited to the South and East by a shale-out in the basinward direction. The field consists of multiple clastic reservoirs; two of them, the 8. TH and 9. TH are subject of an ongoing redevelopment program. Both reservoirs are of Middle Miocene age, were deposited in a shallow marine environment and are characterized by complex reservoir architecture. In order to prepare a redevelopment after more than 60 years of production, various integrated G&G studies consisting of seismic, regional geology, sequence stratigraphy and core analysis (e.g.) were carried out and integrated in separate 3D geologic models that were repeatedly revised and enhanced. Results from reservoir simulation were used to further improve static models (and vice versa). The findings of a recent six well drilling campaign with a tailored data acquisition and analysis program allowed an in-depth reality check of work carried out so far and the planning of follow-up G&G work. The aim of this approach was a holistic view of the two reservoirs with the purpose of identifying the best remaining drilling locations. The secondary objective was to build more precise static models implementing workflows agreed and accepted by all disciplines involved. Extensive comparison of the models with newly acquired data resulted in an improved understanding of the reservoir and also in the abandonment of ‘established’ knowledge. Examples of successfully applied working techniques range from a sequence stratigraphic interpretation system to depositional environment maps. Some analytical techniques applied did not produce good results; the geoscientific reasons for this were analyzed; the less successful approaches identified will be avoided in the future. Structured and repeated reality checks were found to be crucial for the continuous improvement of the subsurface models. Workflows to be followed were developed; they led to a prioritization of work, allow faster updates of models and enable an optimized selection of future well locations.