Determining the viscosity of a hydrocarbon reservoir fluid that is present
in a formation layer traversed by a borehole, which method involves the steps of
selecting a location in the formation layer; lowering in the borehole to the location
a tool that has a central conduit having an inlet, means for displacing fluids
through the central conduit, and an optical fluid analyzer; making an exclusive
fluid communication between the formation and the inlet of the central conduit;
obtaining a spectrum of the optical density; calculating a first factor that is
the maximum optical density in a predetermined short-wavelength range multipled
with the length of the short-wavelength range, calculating a second factor which
is the integral over the same short-wavelength range of the spectrum, subtracting
the second factor from the first factor to obtain a hydrocarbon oil property; and
obtaining the magnitude of the in-situ viscosity from the oil property using a
relation that has been obtained by fitting a curve through previously obtained
data points having the measured magnitude of the actual viscosity as a function
of the oil property.
