Abstract
The CT imaging technique together with temperature and pressure measurements were used to follow the steam propagation during steam and steam foam injection experiments in a three dimensional laboratory steam injection model. During the design period, the advantages and disadvantages of different geometries were examined to find out which could best represent radial and gravity override flows and also fit the dimensions of the scanning field of the CT scanner. As a result of this analysis a 3D rectangular box with dimensions 20x20x7.5 cm was constructed. This box simulates one quarter of a five spot pattern. Aluminum, Teflon™ and Fiberfrax™ were chosen as supporting and insulating materials. Teflon™ was placed between the porous medium and the aluminum shell so that the rate of heat transfer in the porous medium would be much faster than that in the aluminum during a steam injection run. During experiments, steam was injected continuously at a constant rate into the water saturated model and CT scans were taken at six different cross sections of the model. Pressure and temperature data were collected with time at three different levels in the model. CT pictures and three dimensional temperature distributions were compared and analyzed in terms of observed steam zone at each section. To do that, CT numbers within the scan section were used to determine the steam and water zones, and with the aid of x-ray pictures the position and propagation of the steam zone were determined. In addition, using the three dimensional temperature distribution measurements at the same times, steam displacement fronts could be drawn at the scan section locations. These pictures and drawings were used to compare the results obtained from classical temperature-pressure monitoring and from CT scans.
During steam injection experiments the saturations obtained by CT matched well with the temperature data. That is, the steam override as observed by temperature data was also clearly seen on the CT pictures.
During the runs where foam was present, the saturation distributions obtained from CT pictures showed a piston like displacement. However, the temperature distributions were different depending on the type of steam foam process used. During the experiment which included non-condensible gas (nitrogen) injection, the temperature distributions, contrary to the saturation distributions, still indicated the presence of steam override, although the override was reduced by the foam. However, when there was no nitrogen the temperature distributions followed the saturation distributions. This may possibly indicate that the nitrogen foam ahead of steam foam caused the difference between temperature and saturation distributions. These results clearly show that the pressure/temperature data alone are not sufficient to study steam foam in the presence of non-condensible gas.
