Abstract

This case study explores rock physics properties of heavy oil reservoirs subject to the steam-assisted gravity drainage (SAGD) thermal enhanced recovery process (Butler, 1998; Butler and Stephens, 1981). Previous measurements —e.g., Wang et al. (1990) and Eastwood (1993)—of the temperature-dependant properties of heavy oil-saturated sands are extended by fluid-substitution modeling and wireline data to assess the effects of pore fluid composition, and pressure and temperature changes on the seismic velocities of unconsolidated sands. Rock physics modeling is applied to a typical shallow McMurray Formation reservoir (depth of 135–160 m) within the bituminous Athabasca oil-sands deposit in western Canada to construct a rock-physics-based velocity model of the SAGD process. Although the injected steam pressure and temperature control the fluid bulk moduli within the pore space, the effective stress-dependant elastic frame moduli are the most poorly known, yet most important, factors governing the changes of seismic properties during this recovery operation. The results of the fluid substitution are used to construct a 2D synthetic seismic section to establish seismic attributes for analysis and interpretation of the physical SAGD process. The findings of this modeling promote a more complete description of 11 high-resolution, time-lapse 2D profiles over some of the earliest steam zones.

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