A prediction and management tool has been developed to predict the long term development of the vertical positions of a decommissioned or abandoned offshore pipeline with respect to the surrounding seabed. The tool has been developed on the basis of the existing PIPESIN model. It enables the model calibration using the actual historical data regarding pipeline seabed interaction. It consists of a management module which enables a comparison of the predicted behaviour of a decommissioned pipeline against the requirements. The tool can be used:
to determine the required measures to minimise inspection frequency and maintenance of a decommissioned pipeline;
to optimise measures to avoid or minimise the risk to pipeline and/or external activities, such as fishing;
to assist in the development of an adequate policy with respect to abandonment of offshore pipelines.
There are today about 3000 km offshore pipelines on the Dutch Continental Shelf of the North Sea connected to the production and transport of oil and gas. For pipelines in operation, annual surveys are required to inspect the pipeline status to be prepared for seabed changes affecting the pipeline integrity. On the basis of survey reports, it is assessed whether the burial depth or cover thickness of a pipeline still meets the requirements. If not, remedial measures are required. If a field is running down and production stops, then relevant pipelines will be decommissioned. Pipeline operators who are now responsible for regular surveys and maintenance of the pipelines may want to stop these activities. There are today no generally accepted international regulations with respect to the decommissioning of oil and gas pipelines. In the Netherlands it is required to empty and clean the pipelines before they are decommissioned but other measures are to be negotiated and depend on the circumstances.
