Flow assurance is an engineering analysis
process to assure hydrocarbon fluids are transported through pipelines in an
economical manner from the source to the destination in a given environment
over the life time of the project.
Flow assurance
covers the whole range of possible flow problems in pipelines such as hydrate
formation, wax & asphaltene deposition, corrosion, erosion, scaling,
emulsions, foaming, and severe slugging.
The avoidance or
remediation of these problems is the key aspect of flow assurance that enables
the design engineer to optimize the pipeline system for the complete operating
envelope including start-up, shutdown & turndown scenarios.
Flow assurance is
a recognized critical part in the design & operation of both onshore &
offshore oil/gas systems.
Following are the
flow assurance concerns that need to be examined:
o
Pipeline rupture from corrosion
o
Pipeline blockage from hydrates
or wax
o
Severe slugging can damage
separator
o
Large pressure drop in
pipelines can cause lower flow than should be
Following
are the flow assurance strategies that need to be adopted:
o
Hydraulic Analysis : acceptable
pressure drops, pipeline size, erosion & corrosion limits
o
Thermal Analysis : temperature
distribution, heat loss
o
Inhibition Analysis : hydrate
inhibitors, wax inhibitors, corrosion inhibitors, scale inhibitors
When is flow assurance required?
The bulk of the flow assurance analysis is
done during the Front End Engineering & Design (FEED) stage.
During detail engineering phase a verification
process may be undertaken based on the following:
o
Changed product specifications
including composition, phase change (GOR, water cut)
o
Change in pipeline routing
o
Changed operating procedures
o
Change in local health, safety
& environmental regulation
Why modeling of pipeline systems is required for flow assurance?
Modeling is a cost effective & tested tool
for flow assurance. Some benefits are:
o
Ease of studying &
optimizing new and existing pipeline systems
o
Facilitates rigorous screening
of various options in existing and potential systems
o
Reduce uncertainty in design
& operation
o
Reduce downtime by giving a
realistic picture of how the system will be
How is modeling of pipeline systems done?
Steady State Modeling:
o
Software such as PIPESIM &
HYSYS can be utilized for steady state modeling
o
Objectives of Steady State
Modeling
o
Determine the relationship
between flow rate and pressure drop along the pipeline and decide the size
based on the maximum allowable flow rate & the minimum allowable flow rate.
o
Check temperature and pressure
distributions along pipeline in steady condition to ensure that the pipeline
never enters the hydrate region during steady state operation.
o
Determine the maximum flow rate
in the system to assure that the arrival temperatures do not exceed any upper
by the separation and dehydration processes or by the equipment design
Transient Modeling:
o
Software such as OLGA and
ProFES can be utilized for transient modeling
o
Transient Cases or Scenarios:
o
Start-up and Shut-down
o
Emergency shut-down
o
Blow-down and warm-up
o
Ramp up or down
o
Pigging / slugging
Objective of transient analysis is to ensure
that the pipeline conditions are maintained to prevent dangerous surge
conditions and to prevent conditions (pressure and temperature) for hydrate
formation.
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