Probabilistic Modeling of Subseismic Faults in the Pelican Field (Block 211/26a), North Sea, Offshore U.K.

Abstract

Small scale faults are believed to play an important role in compartmentalizing the Jurassic (Brent Group) reservoir in the Pelican field, yet not all these faults can be resolved even with the available modern 3-D seismic. Fault prediction below the limit of seismic resolution has therefore been attempted, using a detailed statistical analysis of the 3-D seismic fault pattern combined with probabilistic modeling techniques. The statistical fault map analysis provides orientation distributions and length and throw frequency diagrams as well as length versus throw relationships. Subseismic fault occurrence (smaller than 40 ft fault throws) is then extrapolated using a fractal model of fault growth and fault distribution. Probabilistic fault patterns are generated and subsequently a Monte-Carlo approach is used to construct probability maps of nonresolved small scale faults. The fault pattern of the Pelican field comprises three main fault orientation sets. A good scale invariance is demonstrated for each set both in terms of length frequency and spatial distribution. This can form the basis for validation of the 3-D seismic interpretation. To test the assumptions of the model, the smallest observed faults are simulated using only the larger observed faults. A good comparison is then obtained between the interpreted andmore » the probabilistic fault patterns. The probability maps highlight the clustering of the small faults and their variation as the minimum size of simulated faults is altered. These maps are used as input for 3-D reservoir simulations. The results lead to an optimization of field development and well planning.« less