Evolution of seismic velocities in heavy oil sand reservoirs during thermal recovery process

TL;DR

This paper investigates how seismic velocities in heavy oil sand reservoirs evolve during thermal recovery processes, using numerical simulations and laboratory data to improve interpretation of 4D seismic monitoring.

Contribution

It extends poroelastic theory to model seismic velocity changes in oil sands during thermal recovery, validated with laboratory measurements.

Findings

Good agreement between model predictions and laboratory velocity data.

Velocity changes can be used to locate steam chambers in reservoirs.

Modeling helps interpret 4D seismic data for enhanced reservoir management.

Abstract

In thermally enhanced recovery processes like cyclic steam stimulation (CSS) or steam assisted gravity drainage (SAGD), continuous steam injection entails changes in pore fluid, pore pressure and temperature in the rock reservoir, that are most often unconsolidated or weakly consolidated sandstones. This in turn increases or decreases the effective stresses and changes the elastic properties of the rocks. Thermally enhanced recovery processes give rise to complex couplings. Numerical simulations have been carried out on a case study so as to provide an estimation of the evolution of pressure, temperature, pore fluid saturation, stress and strain in any zone located around the injector and producer wells. The approach of Ciz and Shapiro (2007) - an extension of the poroelastic theory of Biot-Gassmann applied to rock filled elastic material - has been used to model the velocity dispersion in the oil sand mass under different conditions of temperature and stress. A good agreement has been found between these predictions and some laboratory velocity measurements carried out on samples of Canadian oil sand. Results appear to be useful to better interpret 4D seismic data in order to locate the steam chamber.