The number of subsea production systems placed in deepwater locations in the Gulf of Mexico (GOM) has increased significantly in the last ten to fifteen years. Currently, API-RP2A (2000 a,b) designates the GOM as a Zone 0 seismic risk area, indicating an area of low seismic activity with an expected horizontal ground motion of less than0.05g, and thus does not require seismic effects to be considered during the design process .However, there have been a number of seismic events with Richter magnitudes between 3.0and 4.9 that have occurred in this region. As a result, questions have been raised regarding the seismic performance of deepwater subsea systems.
This study presents an analytical parametric study where a prototype subsea structure was selected based on a survey of subsea systems. The baseline analytical model consisted of a single casing embedded in soft clay soils, which supported a lumped mass at a cantilevered height above the soil. A number of the model characteristics were varied in the parametric study to simulate the structural response of a range of subsea structures. This study examined the impact of API-RP2A Zone 1 and 2 design seismic demands for the performance of subsea structures to provide a conservative bound for the performance of a Zone 0 area such as the Gulf of Mexico. The results from the subsequent analyses show that the stresses and deflections produced by the Zone 1 and2 peak ground accelerations fall within the allowable design limits.