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2.H.3.d
Viscosity
The next figure illustrates the response with default parameters but varying the fluid viscosity.
Values for
are 0.2, 0.5, 1, 2 and 5 cp. If we compare the response with the
Fig. 2.H.8illustrating the effect of a permeability change (above), we see that the sensitivity to viscosity
is exactly opposite to the sensitivity to permeability. At early time (Storage) and middle time
(IARF), the derivative responses have the same shape but translated along the wellbore
storage line of unit slope. When the viscosity is lower, the reservoir reacts faster and deviates
earlier from pure wellbore storage. The levels of stabilization of the derivative and the semilog
slopes are proportional to
. At late time all derivative signals merge to a single unit slope. In
other words, the sensitivity on 1/
is the same as the sensitivity to k on all parts of the
response. This means that we have another governing group with k/
also called the mobility.
Fig. 2.H.17 – Effect of the fluid viscosity, loglog plot
Fig. 2.H.18 – Effect of the fluid viscosity, semilog and history plot