Decommissioning entails the safe plugging of holes used for offshore oil or gas extraction in the earths surface and disposal of all the equipment used. In the petroleum sector, decommissioning is rapidly developing as a market with huge potentials as well as risks. This sector is a source of liability for the contractors, operators, counties and public. Therefore, managing it cost effectively calls for a complete understanding. Gas and oil industries create a circular economy since most of the petroleum products almost serve similar purposes. After extraction has taken place and abandonment of their extraction has taken place, decommission must take place. Decommissioning can be carried out using various techniques such as piece small, piece large, single lift, refloating and other techniques depending on the costs related to the facilities involved.
Petroleum sector provides significant opportunities ranging from decommissioning and reuse to unlock the value of the facilities and other materials that were used in the gas and oil extraction. Globally, there is a wide range of structures and platforms that makes the array of decommissioning techniques a consideration while selecting the best method for the size, stage, and kind of asset. Various methods can be applied to jacket structures and platform topsides. Removal of these structures depends on some factors such as overall costs, availability of resources and the nature of the platform structure.
This technique involves the removal of platform topsides in smaller pieces that dont exceed twenty tons. The pieces are later lifted by either temporary cranes or existing platform cranes onto the barge or supply boat . However, this technique may not be the most appropriate for platform jackets that involve concrete or steel. Such platform jackets need to be removed separately and if possible by not this method. Due to the fixed steel on the earths surface, a single lift is challenged due to the huge mass and dimensions of the structure . This challenge is solved by having the piece small shit that removes small pieces of the components. The small piece lift also solves the problem of removing the reversed installation methods .
Fig. 1. An image for piece small technique
Piece large technique includes the reverse installation methods and modular removal. The platforms are removed in large masses that exceed twenty tons but with a maximum of approximately 5000 tons . The top side equipment is first mechanically separated and installation of lifting points installed. Various modules are separately lifted onto a barge directly. This method is appropriate for the removal of the steel jackets . While under the water, the steel jackets can be cut into subsections and these subsections collected separately onto a barge or the supply vessel. Piece large decommissioning technique is a very effective technique since it may provide more than 95% recycling percentage which is an ecologically best way for the management of redundant offshore installations.
Fig. 2. An image for the piece large technique
Single lift methodology applies when the structure entire topside platform can be lifted as a single unit and removed. The current machines can hold a maximum weight of 48,000 tons . Single lift method necessitates that the topsides design possesses a structural integrity to allow the functioning of the lift or else structural reinforcements are employed. This technique is the most suitable for the steel jacket platforms even though most concrete jackets are usually heavy and dont have sufficient structural integrity. The single shit technique offers a game-changing methodology to the offshore decommissioning since it can easily transfer a complete structure entailing the production platforms within a single movement from the onshore to offshore.
Fig. 3. An image for the single lift technique
The refloating technique applies to the removal of the jackets after the topside platform has been lifted. In the removal of the steel jackets, buoyancy tanks are attached to the pillars of the structure and used to remove the structure from the bed of the sea . Then the Jackets are floated onto the water shelter where they can be easily cut up into pieces either large or small and lifted. At the end of their lives, some engineers designed some concrete jackets to refloat. However, this has not been critically reviewed and therefore unknown whether the technique will be technically feasible. During the decommissioning the floatation concept is insignificant. It worth noting that majority of the offshore decommissioning in the UK uses the single shift technique due to its cost and labor effectiveness.
Fig. 4. An image for the refloating technique
Purging and Cleaning Technique for Pipeline Decommissioning
Pipelines can be decommissioned through purging and cleaning. Cleaning is considered as the most efficient way in which mechanical pigs and if pig receivers and launchers arent available it is important to provide them temporarily . Pigging doesnt apply to lines that have a diameter of fewer than four inches due to the fear of blockage. It is necessary to create small bore lines that enable the clearance of the product with a cleaning agent before the final decomposition of the line takes place. The two liquids or gasses should be separately kept in the line by the use of soft pigs that are deformable.
It might be necessary to many trains of the cleaning pigs as the limitation of the length of a train being the pressure exerted to move a train including the residue that it displaces should not be more than the maximum pressure that should work in a pipeline . It is important to also consider the likely conditions and the age of the line. In instances of flexible connections, the particular solvents for the elimination of the residue have to be compatible with the horse materials and soft lining.
Fig. 5. Purging and Cleaning Pipeline Decommissioning
Fusion bonded proxy and paint among others thin film linings are supposed to be softened by the use of cleaning pigs and solvents. Thin materials come out of the pipe wall as a scale that could block the pipe if too much of it loosens . A suspension gel is smeared in the slugs ahead in case the loosening is likely to happen before the first three moves of the cleaning pig train.
For the purpose of protecting the environment and safety, it is crucial that the decommissioning and pre-commissioning process are fixed by caution setting down of the relevant procedures that list the aim of each stage and the roles of all the personnel involved . It is also imperative to include the actions, equipment, and materials that will be used.
Decommissioning costs after Abandonment
Removal of the abandoned facility involves high costs due to risks involved in the process. The cost for removing the equipment revolves around various critical factors. The list is long, but the main determinants for the gas and oil equipment depend on the location, functions involved, time and the depth of the extraction be it on water or earth surface . There are other factors considered before engaging in the decommissioning market. The main relative factors in the decommissioning platform directly related to the mass of the materials that need to be removed. Operations that focus on removal and disconnection save on extra costs for the decommissioning process . However, almost two-thirds of the costs used for decommission come from the removal costs that makes it important to find contractors with experience, service and great equipment.
In the case of bankruptcy, every party is accountable for the decommissioning costs for the gas and oil goods abandoned. Low prices of both the gas and oil have led to the tremendous increase of energy firms who seek to abandon or sell interests in gas and oil assets in insolvency proceedings . Whether firms strive to abandon or sell its assets, the costs related to the abandoning and plugging or decommissioning not only occurs for the debtor and the potential buyers but also for the joint interest holders, lessors of the debtor and interest predecessors . Every party holds a potential liability for the costs related to decommissioning not met by the debtors estate.
Due to the high costs involved in the decommissioning process, there are other alternatives to the process. Operators may decide to reuse some parts of the offshore equipment. On consideration, some of the factors such as the wear and tear, parameters and the intent of use the operators have to choose some components or the entire equipment for reuse. Examples of such parts include the production of wellheads and manifolds.
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"Offshore decommissioning -", Petrowiki.org, 2015. [Online]. Available: http://petrowiki.org/Offshore_decommissioning. [Accessed: 07- Apr- 2017].
 John Brown Engineers and Constructors Limited, "The Abandonment of Offshore Pipelines: Methods and Procedures for Abandonment," Crown Unit., p.1- 229, 1997.
R. Oran and D. Reiner, "Who Is Responsible for Decommissioning Costs for Oil and Gas Assets Abandoned or Sold in Bankruptcy? | Energy Litigation | ABA Section of Litigation", Apps.americanbar.org, 2016. [Online]. Available: http://apps.americanbar.org/litigation/committees/energy/articles/winter2016-0216-who-is-responsible-decommissioning-costs-oil-gas-assets-abandoned-sold-bankruptcy.html. [Accessed: 07- Apr- 2017].
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