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Swell Test Experiment

In the context of miscibility, a swell test can be used to estimate the first constact minimum miscibility pressure (MMP\(_{FC}\)). The general concept of a swell test is to take an initial reservoir fluid and mix an injection fluid (typically a relevant injection gas) to estimate the miscibility effects of the given injection fluid with the reservoir fluid. Normally the results are given in a swell test plot (see Figure 1). A swell test plot shows the saturation pressure and type with respect to the relative moles injected (RMI). The definition of the RMI is given by

where \(F_{inj}\) is the fraction of injected gas with respect to the entire number of moles in the mixture (i.e. \(F_{inj}=n_{inj}/(n_{inj}+n_{RF})\)).

Procedure

Animation of the swell test PVT experiment

Animation 1: Animation of swell test procedure.

The procedure of the swell test is given as a step-by-step guide below and is shown in Animation 1 for a single step in the procedure.

  1. Initiate reservoir fluid at pressure and temperature.

  2. Mix fluid in step 1 with increment of injection gas.

  3. Pressurize mixture in step 2 to some pressure above the saturation pressure.

  4. Decrease the pressure by applying a CCE to estimate the saturation pressure and saturation type.

  5. Record saturation pressure estimate and saturation type with the relative moles injected and add to the swell test plot (see Figure 1).

  6. Take the new mixture at its saturation pressure and return to step 2.

Results

Once the swell test data is found, the MMP by first contact is determined by the largest value of the swell test data. An example of the swell test data and the MMP by first contact is given in Figure 1.

Example figure of swell test data

Figure 1: Example of swell test data and indicated MMP by first contact.

Note that there is some experimental evidence showing asymptotic behavior of the swell test curve (i.e. the curve "blows up") which yields no MMP\(_{FC}\).