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6.B
Vertical well with Constant Skin
The simplest model is a vertical well fully penetrating the reservoir producing interval.
This is the model used to derive the basic equations in the chapter on ‘Theory’. This model is
sometimes called ‘wellbore storage & skin’, reference to the original type-curves of the 1970’s.
The reason is that the two only parameters affecting the loglog plot response will be the
wellbore storage and the skin factor. However, wellbore storage is a wellbore effect and skin is
used in complement of all other models.
So we will stick to the term ‘vertical well’, considering that ‘fully penetrating’ is the default
status of a vertical well, otherwise the model will be called ‘limited entry’ or ‘partial
penetration’ (see other sections in this chapter).
The behavior of a vertical well in a homogeneous infinite reservoir has already been presented
in previous sections and is shown here as a reminder. The loglog and semilog plots below show
the response for various values of the skin factor (S).
On the loglog plot, the shape of the derivative response, and with a much lower sensitivity the
shape of the pressure response, will be a function of the group C.e
2S
.
Fig. 6.B.1 – Effect of skin, loglog plot