Decommissioning of offshore

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Decommissioning oil and gas installations can cost operators anaverage of $4-$10 million in the shallow water Gulf of Mexico. Thuswhen the US Department of the Interior Bureau of Ocean EnergyManagement, Regulation, and Enforcement (BOEMRE) Gulf ofMexico OCS Region issued a new decommissioning regulation inSeptember 2010, operators knew they'd take a hit.

NTL 2010-G05 requires wells that have not been used for the last fiveyears to be to be permanently abandoned, temporarily abandoned, orzonally isolated within 3 years after Oct. 15, 2010. If wells are zonallyisolated, operators have 2 additional years to permanently ortemporarily abandon the wellhead. Plus, platforms and supportinginfrastructure that have been idle for five or more years must beremoved within 5 years as of the Oct. 15, 2010 effective date.

This new NTL on top of the typical volume of decommissioning workin the GOM will increase demand for contractors and, in turn, theirdayrates.

According to a BOEMRE statement, the MMS (former name of theBOEMRE) conducted an Alternative Internal Control Review (AICR) ofidle structures and wells on active leases in the GOM OCS in 2008.The review identified a significant number of idle platforms that need tobe permanently plugged and removed. Why? Idle structures and wellscould be damaged in a hurricane and cause an environmental disaster.Plus, damaged platforms and wells cost more to decommission thannon-damaged wells.

How Is An Offshore Rig Decommissioned?

There are 10 steps to the process: Project Management, Engineeringand Planning; Permitting and Regulatory Compliance; PlatformPreparation; Well Plugging and Abandonment; Conductor Removal;Mobilization and Demobilization of Derrick Barges; Platform Removal;Pipeline and Power Cable Decommissioning; Materials Disposal; andSite Clearance. Each step is discussed below.

Project Management

Project management, engineering and planning for decommissioningan offshore rig usually starts three years before the well runs dry. Theprocess involves:

review of contractual obligationsengineering analysisoperational planningcontracting

Due to the limited number of derrick barges, many operators contractthese vessels two to three years in advance. In addition, much of thedecommissioning process requires contractors who specialize in aspecific part of the process. Most operators will contract out projectmanagement, cutting, civil engineering, and diving services.

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Permitting And Regulatory Compliance

Obtaining permits to decommission an offshore rig can take up tothree years to complete. Often, operators will contract a localconsulting firm to ensure that all permits are in order prior todecommissioning. Local consulting firms are familiar with theregulatory framework of their region.

An Execution Plan is one of the first steps in the process. Included inthis plan is environmental information and field surveys of the projectsite. The plan describes a schedule of decommissioning activities andthe equipment and labor required to carry out the operation. Anexecution plan is required to secure permits from Federal, State, andlocal regulatory agencies. The BOEMRE will also analyze theenvironmental impact of the project and recommend ways to eliminateor minimize those impacts.

Federal agencies often involved in decommissioning projects includeBOEMRE, National Marine Fisheries Service, US Army Corps ofEngineers, US Fish and Wildlife Service, National Oceanic andAtmospheric Administration, US Environmental Protection Agency, USCoast Guard, and the US Department of Transportation, Office ofPipeline Safety.

Platform Preparation

To prepare a platform for decommissioning, tanks, processingequipment and piping must be flushed and cleaned and residualhydrocarbons have to be disposed of; platform equipment has to beremoved, which includes cutting pipe and cables between deckmodules, separating the modules, installing padeyes to lift themodules; and reinforcing the structure. Underwater, workers preparethe jacket facilities for removal, which includes removing marinegrowth.

Well Plugging And Abandonment

Plugging and abandonment is one of the major costs of adecommissioning project and can be broken into two phases.

The planning phase of well plugging includes:

data collectionpreliminary inspectionselection of abandonment methodssubmittal of an application for BOEMRE approval

In the GOM, the rig-less method, which was developed in the 1980s, isprimarily used for plugging and abandonment jobs. The rig-lessmethod uses a load spreader on top of a conductor, which provides abase to launch tools, equipment and plugs downhole.

Well abandonment involves:

well entry preparationsuse of a slick line unitfilling the well with fluidremoval of downhole equipmentcleaning out the wellboreplugging open-hole and perforated intervals(s) at the bottom ofthe wellplugging casing stubsplugging of annular spaceplacement of a surface plugplacement of fluid between plugs


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Plugs must be tagged to ensure proper placement or pressure-testedto verify integrity.

Conductor Removal

According to BOEMRE, all platform components including conductorcasings must be removed to at least 15 ft below the ocean floor or toa depth approved by the Regional Supervisor based upon the type ofstructure or ocean-bottom conditions.

To remove conductor casing, operators can chose one of threeprocedures:

Severing, which requires the use of explosive, mechanical orabrasive cutting

1.

Pulling/sectioning, which uses the casing jacks to raise theconductors that are unscrewed or cut into 40 ft-long segments.

2.

Offloading, which utilizes a rental crane to lay down eachconductor casing segment in a platform staging area, offloadingsections to a boat, and offloading at a port. The conductors arethen transported to an onshore disposal site.

3.

Mobilization/Demobilization And Platform Removal

Mobilization and demobilization of derrick barges is a key componentin platform removal. According to BOEMRE, platforms, templates andpilings must be removed to at least 15 ft below the mudlline.

First, the topsides are taken apart and lifted onto the derrick barge.Topsides can be removed all in one piece, in groups of modules,reverse order of installation, or in small pieces.

If removing topsides in one piece, the derrick barge must havesufficient lifting capacity. This option is best used for small platforms.Also keep in mind the size and the crane capacity at the offloadingsite. If the offloading site can't accommodate the platform in onepiece, then a different removal option is required.

Removing combined modules requires fewer lifts, thus is a time-savingoption. However, the modules must be in the right position and have acombined weight under the crane and derrick barge capacity.Dismantling the topsides in reverse order in which they were installed,whether installed as modules or as individual structural components, isanother removal option and the most common.

Topside can also be cut into small pieces and removed with platformcranes, temporary deck mounted cranes, or other small (lessexpensive) cranes. However, this method takes the most time tocomplete the job, so any cost savings incurred using a smaller derrickbarge will likely be offset by the dayrate.

Removing the jacket is the second step in the demolition process andthe most costly. First, divers using explosives, mechanical means,torches or abrasive technology make the bottom cuts on the piles 15 ftbelow the mudline. Then the jacket is removed either in small pieces oras a single lift. A single lift is possible only for small structures in lessthan 200 ft of water. Heavy lifting equipment is required for the jacketremoval as well, but a derrick barge is not necessary. Less expensivesupport equipment can do the job.

Pipeline And Power Cable Decommissioning

Pipelines or power cables may be decommissioned in place if they donot interfere with navigation or commercial fishing operations or posean environmental hazard. However, if the BOEMRE rules that it is ahazard during the technical and environmental review during the


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Source: gomr.boemre.gov

permitting process, it must be removed.

The first step to pipeline decommissioning in place requires a flushingit with water followed by disconnecting it from the platform and filling itwith seawater. The open end is plugged an buried 3 ft below theseafloor and covered with concrete.

Materials Disposal And Site Clearance

Platform materials can be refurbished and reused, scrapped andrecycled or disposed of in specified landfills.

To ensure proper site clearance, operators need to follow a four-stepsite clearance procedure.

Pre-decommissioning survey maps the location and quantityof debris, pipelines, power cables, and natural marineenvironments.

1.

Post decommissioning survey identifies debris left behindduring the removal process and notes any environmentaldamage

2.

ROVs and divers target are deployed to further identify andremove any debris that could interfere with other uses of thearea.

3.

Test trawling verifies that the area is free of any potentialobstructions.

4.

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Decommissioning of offshore

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