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The next figures illustrate the ‘skin versus rate’ plot, which is used to evaluate the rate
dependency and the skin if no turbulence was present. From this we can determine a rate
dependent skin model. Finally we see n the history match plot that the model is consistent
with the measured data.
Fig. 6.C.3 – Skin vs. rate plot
Fig. 6.C.4 – History match, rate dependant skin
6.C.2
Time dependent well model
After a stimulation job or a full workover, there is often a voluntary change from one well
model to another. This can typically be the change of the well conditions from a wellbore
storage and skin type to a fracture model after a ‘frac’ job. The skin can also change but the
transformation of the model is more radical than just an improvement or deterioration of the
skin. The other well models are discussed and developed later in this chapter but since the
change of the full well model is similar to that of just a straight forward time dependent skin,
we will briefly discuss it here.
The most common example of a well model transformation is when a well is subject to fracture
stimulation. Typically the well is damaged and no fracture is intersecting the well during the
first status or time period of a well test. Then the well is subject to the ‘frac’ job and the well
model is changed to fracture model. It is possible to model this using a time dependent well
model. The history is divided into time periods with a certain status, and each status can have
the following definitions:
Status with constant wellbore storage and skin
Status with changing wellbore storage
Rate dependent skin for each status
Status with infinite, uniform flux or finite conductivity fractures
Each status can have a different geometry limited entry
Each status can have a different horizontal well geometry