Using 4D Seismic Data to Understand Production-Related Changes in Enfield, NWS Australia

Abstract

The Enfield oil field, located in the North West Shelf, Australia, began production in July 2006. In 2007 a 4D monitor survey was acquired to obtain a better understanding of injector pathways, stratigraphic and fault controlled reservoir connectivity, reservoir pressures and water front movement. A dedicated baseline survey was acquired in 2004 with good image quality. The monitor survey, acquired 7 months after production, is the first dedicated 4D monitor survey in Australia. Both base and monitor optimise 4D repeatability and they were processed in parallel to enhance production-related effects. A series of 4D modelling studies were conducted to decide the criteria for successful 4D interpretation. Pressure and saturation changes were modelled to determine the impact of production-related effects on the 4D. The competing effects of pressure and saturation on seismic amplitudes are complex, therefore an additional 3D swath was acquired over a water injector whilst injecting. This approach helped to calibrate pressure and saturation effects and identify preferential pathways within the main producing interval. The rock properties vary across the field with the eastern most area requiring AVO interpretation to determine fluid movement. In this paper we will present the initial 4D interpretation results using both conventional seismic and AVO volumes and describe how the results were integrated with production and geological data.