The design of HP/HT pipelines to account for the phenomena of pipeline stability, ratcheting and lateral buckling is often complex and time consuming, requiring extensive use of Finite Element Analyses. At the FEED stage of a project the well locations often change and the pipeline routes need to be quickly reassessed. In this case simpler but reliable methods to assess the potential issues need to be employed. This paper outines the methodology employed to perform these assessments at the early stages of a project. The development of a program to assess lateral stability of curves is an important feature of the toolkit, along with a program to assess the impact of bathymetry and freespans. These programs giveresults that closely match equivalent Finite Element Analyses, but in a significantly shorter time. The final verification of only the critical cases can then be performed by Finite Element Analysis. A method to assess the potential for lateral buckling and to define required mitigation is also presented.
In the early stage of a project, in the conceptual or feasibility studies, the field layout is defined by well positions and the host facility will be placed at different locations in order to assess the development costs. As the study moves into the Front End Engineering and Design (FEED) phase, the pipeline routing is looked at in more detail, but the well positions and even host facility may continue to move. For each alternative layout the pipeline stability needs to be verified efficiently but rapidly in order to fix a robust field layout. Depending on the development this may require verification of production and injection pipelines and maybe an export line.
The main issue met at this stage is the lack of precision or even absence of soil data, which is one of the main parameters for verifying pipeline stability. Indeed, different sets of soil parameters are often used in sensitivity studies, and so the number of calculations is multiplied.
The problems to be tackled are at a minimum:
free span identification;