​Saturation Monitoring

Saturation profiles are becoming more and more important for the selection of representative samples for laboratory testing, and for the interpretation of displacement processes in the laboratory. Most of the advanced experimental testing at full reservoir conditions are now performed using either X-ray or gamma attenuation for in-situ saturation monitoring. Normally this will give a saturation profile along the plug sample (as shown in the figure below).

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The example above really illustrates the importance of in-situ-saturation monitoring for proper interpretation of obtained experimental results (the difference in counts shown are proportional to saturation change at each location). Normally, interpretation methods rely on assumptions such as uniform saturation profile (i.e. homogeneous material and no capillary end effects). As can be seen from the figure above, this composite core sample is neither homogeneous nor without capillary end effects. The use of multiple pressure ports and numerical simulation of the displacement are two frequently used methods to correct for non-uniform saturation profiles.

Further, many of the advanced R&D laboratories now uses CT technology to obtain a 3D image of the sample and the displacement process. The following video shows CT scans of different radial cross sections along a whole core sample. Such scans are frequently used to avoid heterogeneous zones and fractures when selecting core plugs for Special Core Analysis.

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The photo below shows an EOR unit utilizing a Medical CT to monitor displacement efficiency by injection of different fluid systems in core samples, using live fluids at full reservoir conditions: