Seismically constrained petrophysics in the Scarborough area^*

Abstract

Despite continued improvements in acoustic logging technology, logs often remain influenced by formation damage and mud-filtrate invasion. Seismic data, another type of measurement that is not affected by drilling, can be integrated in the understanding of incorrect log readings resulting from damage in the immediate vicinity of the wellbore. An iterative workflow of log conditioning, petrophysical interpretation, rock physics modelling, and synthetic-to-seismic matching is applied to ensure the P-sonic and density logs represent the true in situ properties of the rocks. Key to this integration is the development of consistent petrophysical interpretations and rock physics models.

In this paper, we discuss how we arrived at a seismically constrained petrophysical interpretation in the Scarborough gas field in the Exmouth Sub Basin, offshore North West Australia. The logs of these relatively old wells were badly affected by deep invasion of the drilling fluids into the gas sand reservoirs. Conditioning of the well logs was essential to replace the poor quality data. The conditioned logs were used to create an initial rock physics model. Synthetic seismograms were then created using the conditioned logs from the rock physics modelling. Through iterating between petrophysics, rock physics, and synthetic-to-seismic matching we arrived at the final interpretation that is consistent with all available subsurface data. The final synthetic-to-seismic matches for the wells were significantly improved. The integration of different subsurface data types through rock physics modelling significantly reduced the uncertainty in the reservoir properties of the Scarborough gas field.