Page 76 - Handbook Of Multiphase Flow Assurance

Hydraulic restrictions boundaries and management 71

EXAMPLES OF UNSTABLE FLOW MITIGATION
An example of a Deepwater system properly designed for hydraulic management may be a flow
line selected with predominantly uphill geometry to mitigate terrain slugs to ensure flow stability
for a longer portion of the field life and with a separator sufficiently sized to receive liquid surges
in late life. Another example as in Table 4.1 is a single line tieback with an artificial lift to mitigate
severe slugging.

Other considerations

Transient commercially available or custom-developed models should to be used for hy-
draulic analysis, upon performance verification against publicly available or commercial
flow data sets and after approval of the relevant project authority.
In general it takes between 3 and 10 years to develop a multiphase flow analysis tool, so the
task is manageable for a capable individual in an academic setting or for a large corporation
research team.
Transient multiphase flow analysis is complex, and tools which have not been verified by
the user should not be considered for application in production system design. Verification
itself is a complex and time consuming undertaking, and it may need to be outsourced to
qualified engineering vendor which has experience in multiphase flow analysis but no vested
interest in a particular tool.
Impact on production should be determined and accounted for if the choking option was
selected in early design for slug mitigation.

Typical pressure drop
One commonly used frictional pressure drop correlation applicable to single-phase flow is
Darcy-Weisbach:
[
∆PPa] = Lf Moody ρ V / (2 D)
2
3
L = pipe length [m], f = friction factor, ρ = fluid density [kg/m ], v = fluid velocity [m/s],
D = inside diameter [m].

TABLE 4.1 Examples of hydraulic instabilities and their mitigation and remediation
Hydraulic examples (from reservoir to
process) Mitigation examples Remediation examples
Flow instability in wet gas wellbore (i.e., Reduce wellhead choke opening Reduce tubing size or use
FBHP < Lift curve minimum P) Artificial lift (boost)
Flow instability in wet gas flowline (i.e., Periodically sweep liquids to Use partial separation
FWHP < P_dew) slugcatcher
Flow instability in riser (severe slugging) Reduce boarding choke opening Artificial lift (gas lift or boost)