Decommissioning

Decommissioning

Pipeline Cleaning Fluid Recovery

Overview

Axis Energy Projects provide a fully engineered turnkey supply of loading and fluid transfer systems to capture and dispose of the contents of trunk or in-field pipelines, including operational procedures, risk assessments and offshore support.

Pipeline Cleaning and Fluid Capture

Operators face considerable expenditure when preparing a pipeline for decommissioning.   One challenge is how to capture and dispose of the pipeline contents, the cleaning fluids, pipeline effluent, and gels, resulting from pipeline cleaning operations, either by pigging or flushing, in a safe and cost effective manner.

Axis Energy Projects provide fluid transfer systems to evacuate the contents of trunk or in-field pipelines offshore via flexible hose systems.  A connection can be made at any suitable location on a platform, PLEM or production manifold and then exporting the fluid to a tanker.  The systems are provided with passive breakaway connectors and actuated release.

We have a rich heritage, over a period of more than 20 years, and a long and successful track record in the provision of loading and offloading systems to the oil and gas industry.   This includes extended well test export systems - where stabilised crude is transferred via a flexible hose, in many different possible configurations, from a drilling rig or EWT vessel to a tanker.  This technology has been adapted for the capture and disposal of fluids produced in cleaning pipelines as part of their decommissioning process.

Entire pipeline contents can be accommodated in a single pigging or flushing run; volumes up to 110,000m3 can be accommodated in a spot market tanker.  Alternative, lower cost non tanker, options are available where handling of smaller volumes of fluid is required

There is potential to knock much of the water put offshore to reduce onshore fluid disposal costs.

These systems can equally be used in conjunction with pigging to and/or from, for example, a Light Well Intervention vessel (LWI).

We have the necessary equipment to provide a complete fluid transfer system available from stock, based on 1,800m Manuli riser grade hose.  Other hoses and equipment can be sourced as may be required for a specific project.

Our solutions allow pipeline cleaning fluids to be efficiently and safely handled offshore.  The ability to knock water out offshore and dispose of the remainder onshore reduces environmental impact and disposal costs.

Associated Decommissioning Services

Axis Energy Projects has specific decommissioning expertise in the following areas:

Structural design and analysis:

  • FE analysis of structural integrity of the platform/jacket as work progresses
  • design of work platforms to enable work to proceed, to support decommissioning equipment
  • design and analysis of lifting equipment, spreader beams, lift points, etc
  • design of grillages and seafastening
  • design assistance regarding load-in (drawing on our civil engineering expertise)
  • design of equipment handling systems
  • barge deck strength checks
  • barge stability analysis
  • mooring of work boats and accommodation modules
  • analysis of equipment to permit re-use
  • design of fluid offtake systems
  • engineering work packages for the removal of topside modules

Subsea Structure Removal:

  • as above but with additional assessments of structure foundations and structure/soil interaction to develop a suitable removal methodology

Moorings, Pipelines & Flowlines:

  • development of fully engineered removal solutions
  • development of subsea chain and wire cutting procedures for moorings removal
  • specification of equipment for chain and wire cutting operations
  • riser laydown analysis and procedures
  • jumper wet parking engineering

Safety:

  • attendance at Hazid/Hazop/HIRA
  • presentation of procedures at the above

Case Studies

FPSO/FSO Decommissioning - Banff Reinstatement Project


Disconnection and crosshauling the production riser from the FSO to the CSV to enable its laydown on the seabedAxis Energy Projects was contracted by DOF Subsea to provide engineering and operational procedures for the Teekay Petrojarl Banff FPSO reinstatement project. The first phase of the project focused on the disconnection and tow in of the STL buoy, used to moor the Apollo Spirit FSO.

Riser Disconnect and Laydown

This commenced with the disconnection of the 12” flexible riser from within the STL buoy so that it could be laid down on the seabed and secured in place with mattresses. Axis Energy Projects provided full structural engineering analysis and design, prepared rigging drawings, equipment lists and deck layouts, developed the operational procedures and storyboards, and presented the procedures to the pre-operational HIRA. 

Subsea Chain Cutting


ROV cutting a mooring chain using a diamond wire sawFollowing the laydown of the riser each 120mm mooring chain was severed subsea using a diamond wire cutter, with the free end of the chain and upper mooring wire being recovered to deck, leaving the lower wire and lower chain segments undisturbed on the seabed. Axis Energy Projects personnel were also responsible for writing the procedures and specifying the equipment for cutting the 120mm chains subsea and cutting the 113mm wires on deck into 12m lengths for recycling.  Once all eight mooring lines were severed, the final upper mooring wire was transferred to an AHT and used to tow the STL Buoy to Invergordon for refurbishment onshore.

The final phase of the project mobilized in April 2014 and encompassed the full reinstatement of the STL buoy in the field.

 Detailed Inspection of a Damaged Pipeline 


During a routine inspection a gas export pipeline in the central North Sea, the pipeline was found to have sustained damage warranting further investigation. DOF Subsea was asked to undertake the work to survey and expose the pipeline, and assist the selected contractor to undertake the detailed inspection of the damage on a fast-track basis. Axis Energy Projects was contracted by DOF Subsea to provide support and assistance with the development of operational procedures and storyboards for diverless dredging, weight coat removal, and detailed inspection of the damaged 28” pipeline.

As Found Survey and Diverless Dredging


An ROV was utilized with a low pressure water jet to clean marine growth and loose concrete coating from the areas of damage. Following this a visual survey of the damaged areas took place.  

An excavation tool was then employed to expose the area beneath the pipeline to provide access for the inspection activities. Following this a dual head multibeam sonar system was used to carry out a multibeam survey of the excavated area. 

Concrete Weight Coat Removal


The ROV was then deployed with a pipeline coating removal tool to remove the concrete weight coat around the damaged area, with a hydraulic cutter being used to cut through the exposed metal rebar and enable the sections of weight coat to be lifted clear.  The coating removal tool was then used to ensure the exposed pipe was sufficiently clean for the required inspection tasks.

Detailed Inspection of the Pipeline

A visual inspection of the pipeline was then carried out, followed by a various detailed inspections using a “ROV-it” inspection tool.  

Note:  Although this scope was not to decommission the pipeline, it does demonstrate the required expertise in many of the tasks necessary to do so. 

Bespoke Drilling Stack Handling Frame - Geoprober

Geoprober Drilling Limited (GDL) supported Shell UK with engineering services associated with the decom   missioning of the Brent Delta GBS platform in the North Sea. Geoprober’s special drilling package was designed to drill through the 1.5m thick reinforced concrete dome of one or more large vertical cylindrical storage tanks surrounding the bottom of the platform’s three legs and to recover the concrete core(s) to the surface. 

Bespoke Drilling Stack Handling Frame

It was envisaged that the drilling tool package would be transported by road from the fabrication yard to an onshore location for testing and thence to the quayside for embarkation on to the vessel Normand Subsea for transit to the Brent Field. Axis Energy Projects was commissioned to design the drill stack’s transportation and handling frame with a tool package cradle to support and manipulate the drilling package whilst in transit on road and at sea, during lifting and testing operations, for embarkation on to the vessel, and for raising the package from horizontal to vertical for overboarding by the ship’s crane and subsequent lowering to horizontal again after recovery. The frame was fitted with walkways, a drilled core recovery system, and a hydraulic system for upending and lowering the drilling package. 

Vessel Modifications and Further Structural Design

The scope of work also included design of the base plate frames, rigging design and the seafastening design of the equipment. 

Kharg Island Jetty Dismantling, Iran


The Kharg Island facility was at one time the world’s largest oil terminal and was the principle sea terminal for exporting Iranian oil. In 2004, the team at Axis Energy Projects were contracted to write the procedures for the dismantling of the eastern T jetty of the terminal, capable of supporting 7 tankers, prior its refurbishment and re-instatement. 

Removal of Subsea Piles

The scope of work included the writing the procedures for the diving scope of the demolition and removal of the piles. 

Reinstatement of Subsea Piles

Axis Energy Projects also wrote the procedures for the reinstatement of the piles, pile heads and primary steelwork, and designed the moorings for the transportation barge and installation barge. As of 2012 the Kharg oil terminal handles roughly 98% of Iran’s crude exports.

Chain Condition Assessment – SEREPT, Tunisia


SEREPT is the operating company of the Ashtart oil field located in the Gulf of Gabes, offshore Tunisia to the East of Sfax. Two offloading single point mooring systems are available on the Ashtart site, PC1 and PC2. Both are able to perform offloading operations. Axis Energy Projects was contracted by SEREPT to review the condition of the PC1 mooring chain which had been removed from the field, sandblasted and stored in two sites onshore to determine if the chain was fit for re-use. 

Chain Inspection 

A close visual inspection of both lengths of chain was carried out, as well as diameter and pit corrosion depth measurements. On the basis of these tests it was found that the one length of chain was not suitable for re-use. The other length of chain showed more consistent measurements, however, it was suggested that the chain be properly cleaned of marine growth to enable more accurate checks.

Recommendations 


In addition to the dimensional criteria investigated onsite, it was recommended that other aspects of the chain characteristics be considered by carrying out a comprehensive MPI test and fatigue life assessment.