Daniel T. Georgi, David W. Pritchard, and Paul A. Hemingson
Esso Resources Canada Limited, Calgary, Alberta
ABSTRACT
In 1987, Esso Resources implemented a vertical sweep pilot in the Judy Creek field to evaluate the impact of gravity override on conformance in the hydrocarbon miscible flood. The pilot pattern is formed by an injector well and three producers and a fiberglass-cased monitor well. Over a period of two years, some 58 induction logs and 30 neutron porosity logs were run to delineate the water and solvent-swept zones and to monitor the evolution of water, oil and solvent saturations during the water, solvent and chase-gas injection.
The interpretation of the log data has relied primarily on the evaluation of the differences between the base logs and subsequent monitor logs. With the use of insitu calibration zones, we have reduced the uncertainty of the differences in deep resistivity measurements to less than 0.2mmho/m. Assuming that formation-water resistivities and the Archie saturation exponent do not vary, we are able to detect changes in water saturations as small as 1%. Although water salinities do not vary significantly, it has been necessary to account for gradual changes in the reservoir temperature. By averaging multiple passes and using insitu calibration data, we have reduced the uncertainty of the epithermal neutron porosity to less than 0.35 p.u. and are able to compute changes in solvent saturations to +/- 5%.
The observation well data permitted us to estimate the flood’s volumetric sweep and to monitor the dynamic changes during the various stages of the flood. The computed water saturations allowed us determine when the residual oil saturations had stabilized. Once the residual oil saturations had stabilized, solvent injection was initiated. During solvent injection, the monitor well permitted us to observe the insitu formation and passage of a tertiary oil bank and the development of the steady—state water-solvent commingled zone. Finally, the observation well data showed the replacement of solvent with chase gas.
The observation well data in conjunction with other reservoir engineering data have played a key role in the management of