Recent developments in design procedures for drilling conductors and for well conductors at fixed platforms have led to an increase in the allowable free spans for conductors. This increase, however, has given rise to new problems, for instance vulnerability to dynamic excitation. The stability criteria for conductors are presented and procedures for calculation of dynamic response, including response due to vortex shedding induced vibrations are presented. The application of these methods for load response in both extreme and fat1gue analyses are outlined. Application of the methods are presented for analyses of a conductor on a fixed platform and for fat1gue analysis of a drilling conductor. Design procedures are described.
Offshore well conductors at fixed platforms comprises an outer casing with several smaller casings inside. This is often referred to as the casing programme. The space between the casings is either filled with cement or taken up by sea water. A number of centralizers may be applied for the inner casings. The inner casings are hanging in the outer casing, thus generating a Compressive load in the outer casing. To this compressive load is further added the weight of the Christmas Tree (or blow-up preventer when drilling). Often this compressive load is large and leads to considerations concerning the buckling stability of the conductor. Recent developments in design methodologies for slender well conductors have taken advantage of the fact that the internal casing strings do not cause buckling of the integrated system. By utilization of these design methods the conductor system will become more slender compared with previous designs and thereby more vulnerable to dynamic excitations. The dynamic behaviour of the well conductor can be divided into two classes: vortex shedding induced vibrations dynamic behaviour due to resonance with wave loading.
