For the last 4 to 5 weeks I am preparing a presentation on pipeline flow assurance for some young engineers of my company.
Now I would like to present an abridged form of that presentation on my blog for the benefit of the forum readers.
Here is how it goes:
"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:
- Pipeline rupture from corrosion
- Pipeline blockage from hydrates or wax
- Severe slugging can damage separator
- Large pressure drop in pipelines can cause lower flow than should be
Following are the flow assurance strategies that need to be adopted:
- Hydraulic Analysis – acceptable pressure drops, pipeline size, erosion & corrosion limits
- Thermal Analysis – temperature distribution, heat loss
- 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:
- Changed product specifications including composition, phase change (GOR, water cut)
- Change in pipeline routing
- Changed operating procedures
- 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:
- Ease of studying & optimizing new and existing pipeline systems
- Facilitates rigorous screening of various options in existing and potential systems
- Reduce uncertainty in design & operation
- Reduce downtime by giving a realistic picture of how the system will be
How is modeling of pipeline systems done?
Steady State Modeling:
- Software such as PIPESIM & HYSYS can be utilized for steady state modeling
- Objectives of Steady State Modeling
- 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.
- Check temperature and pressure distributions along pipeline in steady condition to ensure that the pipeline never enters the hydrate region during steady state operation.
- 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
- Software such as OLGA and ProFES can be utilized for transient modeling
- Transient Cases or Scenarios:
- Start-up and Shut-down
- Emergency shut-down
- Blow-down and warm-up
- Ramp up or down
- Pigging / slugging
Comments from valued readers of the forum are most wecome.