Modelling Fluid Distribution in a Chalk Field Using Elastic Inversion

The strong correlation between porosity and P-impedance observed in carbonates fields has allowed us over the years to use seismic inversion as a reliable way to estimate porosities. It is widely accepted that estimating fluid distribution in carbonates using seismic is a rather difficult task. We have shown that it is possible to map fluid distributions in chalk reservoirs using elastic inversion and Bayesian classification constraint by wells and detailed rock physics. This study was carried out over a field in the Danish North Sea, where the main producing reservoir unit is a 50ft thick chalk with high and almost constant porosity; allowing us to associate most of the changes in the seismic to changes in fluid type and saturations. A seamless integration of petrophysics, rock physics, geomodelling and seismic elastic inversion; has allowed us to improve the definition of the top of the reservoir unit and guide the fluid distribution; hence providing a significant more reliable saturation model away from well control in the reservoir model. A blind well showed a good match between the observed saturation and the predicted saturation based on inverted seismic and other wells. We were also able to predict the OWC with good accuracy.