Pipeline Loads and a Design Approach in Areas of Seabed Subsidence

Abstract

Seabed subsidence may sometimes be a consequence of the drainage of the oil and gas reservoir. The subsidence process results in changes of the seabed level as well as displacements of the seabed horizontally. The horizontal displacements may impose significant axial compression or tension loads on seabed pipelines installed in the area. This paper focuses on the engineering challenges of pipelines subject to seabed subsidence. The paper deals with the design issues of the pipelines. It will be seen that for pipelines in areas of seabed subsidence an overall design approach applies where pipeline integrity management may be an important part of the solution. The present paper describes the phenomenon of seabed subsidence including a typical subsidence field and the time history of vertical and horizontal displacements of the seabed. An example pipeline route is defined for the purpose of illustration of displacements along the route. A pipeline to be designed and installed in the subsidence area is defined. The load transfer mechanism from seabed to pipeline is described and the resulting compression or tension loads from seabed subsidence on the pipeline are then derived. An approach for designing a solution for the pipeline to accommodate the loads from seabed subsidence is established and discussed. The discussion involves spool design, mitigation measures and integrity management issues. The paper concludes by recommendations for future applications in actual design cases.