Geotechnical Considerations in Well Casing Design

Offshore well casing must be designed to be not only structurally, but also geotechnically stable in accordance with API or other similar standards. Understanding the interaction of well components with the surrounding sediments is imperative, as it is these sediments that provide the resistance to applied vertical, lateral and torsional loading during both installation and operation of the well. At each stage of construction, from the placing of the temporary guide base to the completion of the well, the surrounding sediments need to resist the loads applied by the self weight of each well component and possible live loadings caused by snagging of any exposed well components or flow lines. The stages of component installation and, most importantly, the geotechnical properties of t h e surrounding sediments must b e fully understood before any loading can be considered.

It has been found that the well and flow line layout also has a significant effect on the governing load combination and careful consideration must be given to possible snag load locations. This paper will outline the different types of geotechnical analyses that must be undertaken for the verification of offshore wells.