Pipeline Decommissioning Process in Oil and Gas
Oil and gas pipelines are designed to serve as a conduit for the recovery and channeling of natural hydrocarbon products. However, like with any other process equipment, these structures will undergo retirement at the end of their useful lifespan.
Decommissioning pipelines ensures all components of a network are safely dismantled/neutralized to prevent a lasting environmental hazard.
What Is Pipeline Decommissioning and Abandonment?
Pipeline decommissioning refers to a series of properly planned and executed actions required to safely remove a pipeline or network of pipelines from activity. Commonly employed methods of decommissioning include pipeline nitrogen purging, pipeline pigging, filling, and plugging.
Pipeline abandonment is another term used to describe a decommissioning procedure. For a pipeline to be accurately designated as abandoned, activities eliminating all the combustible fluids it conducted during its service life must be carried out. Additionally, all connections to active production channels must be severed and all associated facilities sealed.
Pipeline decommissioning and abandonment are generally conducted for two main reasons:
- A pipeline has reached the end of its useful lifespan and further use is no longer economically viable.
- The oil and gas reserves it serves has been exhausted and as such, there is no longer a product for conveyance.
Offshore vs. Onshore
Pipeline decommissioning procedures vary depending on the location in which they are carried out. These activities can be broadly divided into offshore and onshore groups based on the location of the pipelines.
Offshore pipeline groups include subsea pipelines and oil rig lines. The procedure for decommissioning oil rigs or subsea pipelines are similar and include pipeline retrieval, retirement in-situ, and preservation on-site for future reactivation. In many cases, offshore operators favor the preservation and retirement in-situ approaches as pipeline retrieval is a very costly engagement in terms of capital and manpower expenditures.
Onshore pipeline decommissioning activities follows a similar pattern to offshore decommissioning but is often a less complex and more inexpensive process.
What Is Pipeline Abandonment in Place?
An abandonment in place strategy refers to the practice of leaving an “inactive” pipeline in the area where it was installed after it has served its purpose. Pipelines left in-situ will undergo standard measures to eliminate fire and explosion hazards including flushing, and pipeline cleaning before they are disconnected from the oil or gas supply and sealed at both ends.
Although the term abandonment is used loosely to refer to pipelines no longer actively trasnporting gas, the Pipeline and Hazardous Material Safety Administration (PHMSA) strictly defines the criteria for abandonment to include purging of all combustibles and irreversible discontinuation of pipeline use.
Is Pipeline Removal Required?
The physical removal of a decommissioned pipeline is not necessary for all structures at the end of their service life. Pipeline recovery is typically reserved for flow lines maintained above the ground targeted for refurbishment and reuse.
Drawbacks to complete pipeline evacuation include:
- Significantly higher costs in terms of capital/manpower expenditure
- Increased risk of environmental/human safety hazards during removal
- Disruption of surrounding ecosystems with possible contamination from residual pipeline contents leaked during excavation
Who Is Responsible for The Pipeline Decommissioning Procedure?
The responsibility for the installation, operation, pipeline safety, and eventual decommissioning of gas pipelines resides solely with the pipeline owners/operators. Dependent on unique legislation, various government agencies mandate the compliance of oil and gas industry players with standards that prioritize the health and safety of its workers and citizens residing in host communities.
In the U.S, the Federal Energy Regulatory Commission regulates all aspects of active pipeline operation and discontinuation of use.
Pipeline Abandonment Regulations – FERC and 49 CFR 192.727
The FERC laid down conditions for pipeline abandonment or deactivation in section 49 CFR 192. 727. Criteria for abandonment include compulsory disconnection, filling, and sealing of pipelines at end of their useful lifetime.
Additionally, the relevant section on pipeline deactivation also mentions exceptions to standard pipeline abandonment procedures and outlines the method of data submission on abandoned facilities.
Onshore Pipeline Decommissioning Process
These processes are conducted for pipeline networks installed on land or below the ground surface. Onshore pipeline retirement approaches include:
- Pipeline flushing with inert gas (typically nitrogen)
- Pipeline cleaning with pig devices
- Disconnection of retiring pipelines from product supply sources
- In-situ abandonment or pipeline recovery, and reuse in alternative processes
For onshore decommissioning where pipeline recovery is favored, operators can channel the materials into scrap metal for reworking into other useful components or refurbish/recycle them for use at another location.
Pipeline decommissioning requires all pipeline operators to disconnect all flow lines intended for retirement from gas reservoirs and other active storage and transport components. This stage of decommissioning is critical to ensuring a safe transition of lines from active to inactive status.
Purging gas lines can be done with an inert gas preferably nitrogen to force out any residual oil/gas left within the pipeline lumens. Inert gas purging limits the risk of fire/explosion from a decommissioned line by eliminating volatile materials and inerting the flow lines.
National Pipeline Mapping System (NPMS) Reporting
The FERC tasks all pipeline operators to submit and continually update data on the status of their pipeline networks. In the U.S, information on all pipelines and associated facilities abandoned after October 10th, 2000 is to be submitted using the National Pipeline Mapping System (NPMS) in compliance with the Standards for Pipeline and Liquefied Natural Gas Operator Submissions.
Data reports can be submitted via mail, fax or emails addressed to the Office of Pipeline Safety, Pipeline and Hazardous Materials Safety Administration, U.S. Department of Transportation.
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