Decommissioning of oil and gas infrastructure will increase over the next decades. Many oil and gas fields are mature and will eventually cease production as they have reached the end of their economic life cycle. A reduced contribution of hydrocarbons is expected in the future energy mix. The decommissioning of infrastructure and the restoration of production and processing sites are part of the exploration and production lifecycle. Similar to the exploration and development activities, the operating company is responsible for the safe, sustainable and environmentally sound execution of this work.
Decommissioning typically takes several years of careful planning before execution starts. It takes many steps involving different stakeholders. Often the operator relies on technical and logistical services from the service industry.
The actual plugging of a single well typically has a duration of several weeks depending on the complexity of the operation. The physical removal of an offshore platform can take anywhere from weeks to months, depending on the complexity and size of the installations. The restoration of an onshore site is a much longer process, often lasting several months. Foundations, cables and pipelines are removed before the location is restored, in agreement with the wishes of the landowner, to its original state.
Decommissioning activities are bound to national and international legislation to which operators must fully comply. Prior to decommissioning a work plan must be submitted for approval by the authorities. The presiding authority is the State Supervision of Mines (Staatstoezicht op de Mijnen).
International agreements are in place regarding the removal of offshore mining installations. OSPAR Decision 98/3 regulates the removal of mining installations after use. The specific requirements are set out in the Dutch Mining Decree (article 5.2.3). For onshore installations and locations, private agreements with the land owner(s) typically govern the decommissioning process. Before decommissioning and removal a work plan must be submitted for approval. In the case of offshore installations, the topsides are typically cut and lifted from the supporting structure by large crane vessels. The supporting structures (jackets) are then separately lifted from the seabed and transported together with the topsides either for re-use elsewhere, or back to shore for dismantling and recycling.
After use, pipelines on the Dutch Continental Shelf must be cleaned and subsequently flushed with sea water, and buried or secured in such a way that other users of the sea are not adversely affected by their presence. Onshore, private agreements with the landowner(s) determine how a pipeline has to be decommissioned after use.
The required measures for the decommissioning of wells are set out in article 8.5 of the Mining Regulations. To permanently seal wells several cement plugs of 100 meters in length are typically placed at various intervals in the well. The well bore is closed off just below the surface and the steel casings are cut several meters below ground level (or below the seabed in the case of offshore wells).