Page 210 - Handbook Of Multiphase Flow Assurance

208 7. Flow assurance deliverability issues

Another cold flow design is static mixer. The static mixer design has been validated in
the field (Turner and Talley, 2008) to control the hydrate formation and to keep hydrates dis-
persed and flowing.
None of the cold flow methods have been implemented for continuous field use due to
novelty and lack of historic performance. Operators are not yet certain whether either cold
flow technique can deliver 100% reliability over the life of field. Cold flow technology may be
useful where the use of chemicals is restricted by local regulation.

Heavy oil viscosity

Heavy oils provide increased resistance to flow not only by being heavy but also by having
higher viscosity.
Over 20 methods are available in literature for estimating oil viscosity. These methods have been
summarized by Bergman and Sutton (2007) who correlated dead oil viscosity with temperature
and density based on 9837 viscosity measurements from 3047 fluids which ranged in API gravity
from 0.45° to 135.9°. The Bergman and Sutton correlation was discussed earlier in Chapter 3.
A recent correlation for estimating the viscosity of heavy oil in mixtures with water has
been presented by Wen et al. (2016). The method proposed by Wen may be used together with
the correlation provided by Bergman and Sutton (2007).

Emulsion rheology
Oil and water emulsion may be more viscous than just oil by a factor of 10 or more. Several
correlations for emulsion viscosity had been developed including Smith & Arnold, Woelflin
Loose, Woelflin Medium and Woelflin Tight.
Emulsions may exhibit peak viscosity around 50–85% water cut. The inversion point from
oil-external to water-external emulsion depends on the character of the crude, the character
of the brine, and the degree of emulsification. The inversion points corresponds to maximum
viscosity (Fig. 7.1).

Emulsion Viscosity
100,000

Effective Emulsion Viscosity, cP 10,000

1000
Smith & Arnold
Woelflin Loose
Woelflin Medium
Woelflin Tight
100
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Water Cut
FIG. 7.1 Effective emulsion viscosity correlations comparison.