Page 86 - Handbook Of Multiphase Flow Assurance

Thermal effects 81

25 mN/m and 60–65 mN/m for gas-water, in field units these are 0.17 lb f /ft and 0.44 lb f /ft.
The authors suggested that heavier water is more likely to accumulate downhole, thus mini-
mum gas velocity to lift water should be used. In an example calculation it equals about 7 ft/s
or 2 m/s for a well with 1000 psi upstream of the tree choke. As pressure drops to 500 psi gas
becomes less dense and can entrain less water so the minimum velocity increases to 10 ft/s
or 3 m/s.
A recent overview for multiphase flow correlations for inclined and horizontal flow in
pipelines is provided in Jerez-Carrizales et al. (2015).
The correlations implemented in commercial software have been extended to use 3-phase
correlations with water, and sometimes with entrained solid particles.
A solids transport model has been presented by Warner and Letizia (2001).
Transient pressure hydraulic analysis is associated with surge calculations and HIPPS
systems. HIPPS systems can provide economic alternative to installing a thick-wall pipe-
line rated to the maximum pressure which may be experienced in the production system.
Instead, only a portion of the system which will definitely experience high pressure will
have a pipe rated to higher pressure for example during a shut-in, whereas the portion
of the production system which will experience lower pressure during production can be
equipped with a pipe rated to a lower operating pressure. The two portions of the pro-
duction system would be separated by a fast acting HIPPS valve which can close in a few
seconds. A short portion of the production system downstream of the HIPPS valve would
still be rated to the higher pressure to account for the pressure increase while the HIPPS
valve is closing. Flow assurance uses transient analysis to determine the length of the rein-
forced pipe downstream of the HIPPS valve. Flow assurance hydraulic analysis for HIPPS
for subsea and for onshore or topsides facilities may rely on API 17TR13, section 10.8, and
API 17O standards.
Flow energy dissipation in gas-dominated systems and in multiphase systems is influ-
enced by conduit roughness. Values for commonly used materials are summarized in the
chapter on reference information.

Thermal effects

Heat transfer

Typical average values for seawater flow velocity is 0.1 m/s and for air 1 m/s. Typical
seawater temperature is 4 °C at depth greater than 1000 m worldwide. Actual values must be
obtained from the recent meteorology and oceanography (metocean) report for the region of
interest, with seasonal variation.
As produced fluids flow from a warm reservoir through progressively colder environ-
ment, heat transfer occurs by conduction and convection. Changes in produced fluid tem-
perature cause phase transitions which cause multiphase flow, solids precipitation and other
engineering challenges. Insulation helps maintain heat in the produced fluid.
Thermal properties of various materials commonly used in production systems are summa-
rized below. These values in Table 4.3 are indicative only. Actual values should be verified for
relevant conditions.