Oil production in the province of Alberta will be increasingly dependent on Enhanced oil recovery (EOR) technology in the next decade. Successful implementation of an EOR process requires a thorough understanding of the reservoir flow behavior. The most difficult parameters to assess in EOR operations are the vertical and areal sweep efficiencies in the reservoir. Spatial and temporal distributions of the injected fluids between existing well locations are necessary quantify these parameters. Contemporary EOR monitoring schemes such as tracer or cased hole logging surveys can only provide flood information after inter-well communication is established. Knowledge of poor sweep conformance prior to breakthrough would allow time for corrective measures to be implemented. A three year joint research program has just been completed and results suggest that repeat seismic surveys can be selectively used to monitor the movement of injected EOR fluids between wells in the reservoir, and thus dramatically improve the opportunity for timely reservoir management.
Some EOR processes impart a change in the acoustic velocity and density of the reservoir rock that can be measured using seismic methods. Laboratory tests have been performed on a wide variety of carbonate and clastic core samples to determine the acoustic effects caused by EOR processes.
The laboratory results show that thermal, miscible or immiscible hydrocarbon solvent, and CO2 floods can all cause significant change in the acoustic properties of the reservoir. Pore pressure variations and water injection can also cause an acoustic change under some circumstances. The magnitude of the acoustic velocity dependency on pore fluid saturation varies considerably in different rock-types. This suggests that laboratory testing should be performed to determine the amount of acoustic change like to occur in the reservoir before seismic monitoring a field is considered.
Seismic modeling has been implemented to predict sismic monitor response based on the acoustic properties measured in the laboratory. Modeling results indicate that solvent, CO2, steam and fire flooding should all be detectable in a wide range of reservoir situations.
Repeat seismic methodology should also be applicable to monitoring of gas production under aquifer or water drive. Gas production during the blow-down phase of a miscible flood is another excellent candidate for this type of monitoring.
Research results indicate that miscible EOR monitoring should be technically successful. Economic justifications must also be met before this technology will become widely used. Geophysical EOR monitoring must be fully integrated with the standard tools of reservoir management in order to demonstrate the increased production efficiency that could offset the cost of the monitoring program. A reservoir management plan that incorporates the use of seismic monitoring information with standard engineering techniques will be presented and contrasted against current exploitation strategies. While the role of geophysical monitoring can be examined in the context of the EOR production, its ultimate value can only be assessed Through the course of actual field trials.
As conventional oil recovery in the province of Alberta declines, there is an increasing need to implement Enhanced Oil Recovery (EOR) techniques in order to maximize production from our existing fields and oilsands deposits.
