| Popis: |
The 16th Torton horizon of the Matzen Field is the largest oil reservoir in Austria. Oil production commenced in 1949. Up to now, 42 mn m3 have been produced from this reservoir. The reservoir is characterised by transgressive sands and calcite layers extending laterally several meters to several tens of meters. These layers are effective vertical flow barriers. To optimise oil recovery, wells were first completed in deeper sections of the sands which are up to 70 m thick and later perforated in upper sections. To identify infill drilling locations in this 58 year old field, an integrated study was performed 2005 – 2006. To achieve a good history match, permeabilities and the extent and presence of thin limestones, the so-called "hard layers", were modified (vertical flow barriers). Four infill drilling locations were identified. To assess the uncertainty in the production forecast for these four wells, assisted history matching and forecasting was performed. Assisted history matching achieved several good matches. Using history matches with the smallest error, several forecasts were generated. In all of the forecasts, the production rates from the infill wells would result in economically attractive projects – hence the four drilling locations were included in the drilling schedule for 2007. Comparing results of the manual and assisted history matching shows that assisted history matching leads to as good as or better global matches for production rates and pressures. Furthermore, assisted history matching gives a range of forecasts which can be used to quantify uncertainty. However, in this reservoir with multiple re-completions and small scale heterogeneities, the well by well history match was better in manual history matching than in assisted history matching. In addition, manual history matching resulted in significantly improving the understanding of the reservoir behaviour and in identifying wells which suffer from poor cementation. |
