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West Brae Field Reservoir Model: from Example of a Petrophysical Simultaneous Inversion from Eocene Turbidites, Central North Sea, UK

Schwab, Anne M.1; Buckner, Steve 1; Cass, Julie 1
1 Marathon International Petroleum G.B., Aberdeen, United Kingdom.

Reservoir understanding of the West Brae Field has improved due to the results of a Petrophysical Simultaneous Inversion (PetroSI). The field was discovered in 1975 with initial production in 1997 from two levels of Early Eocene turbidite sands in the Balder and Sele Formations (Flugga sand member). Both turbidite sands are good quality with average porosity of 30%, an average N/G of 85%, and permeability up to 7500mD. The field produces mainly oil (22°API) with a dry gas cap, and has two distinct oil-water contacts. A high quality 4D seismic data set was acquired in 2007, which was parallel processed with the 1993 baseline seismic. This new data prompted a rebuild of the reservoir model to assess the potential for by-passed hydrocarbons.

The Petrophysical Simultaneous Inversion (PetroSI) technique reconciles an existing geologic model with actual seismic measurements using rock physics. An initial geologic model, in depth, with petrophysical properties (i.e. porosity and Sw) is converted to an elastic time model (Vp, Vs, RhoB) using Petro-Elastic Models (PEMS). This elastic model is converted into synthetic seismic angle stacks. The synthetic seismic angle stacks are then compared to actual seismic angle stacks, from the 1993 baseline seismic, and analysed for matching criteria. A simulated annealing algorithm is used to minimize the residuals of this criteria through perturbations of the initial petrophysical property model (i.e. porosity and Sw). The output is an updated geologic model, in depth, containing petrophysical properties consistent with actual seismic measurements.

The current West Brae Geomodel is the result of a multidisciplinary reservoir characterization study using the PetroSI technique. This presentation will review the methodology adopted to integrate 3D seismic data into the West Brae static geological model. This model was used as a starting point for further optimisation utilising reservoir simulation and the results of the 4D seismic. The resultant Geomodel is currently being used to optimize new well locations in West Brae.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009