Numerical Simulation in time domain of a surface casing under platform motion forced oscillation, current and waves loadss

The Santos Basin Pre-Salt Cluster has the deepest production well off Brazil. The wellheads are in more than 2000 m of water depth. From the seafloor, the wells must cross over 1000m of sedimentary formation and about 2000 m of salt layer to reach the carbonatic reservoir. This makes the Pre-Salt wells deeper than a Post-Sal well located in the Campos Basin. A typical development well in Santos Basin is drilled in 4 phases. In this article, our focus is the dynamic response of the surface casing, which is the casing string installed in the second phase of drilling. A Pre-Salt well has a surface casing of about 1000 m long and a Post-Salt well has 400 m long surface casing. In both cases, the surface casing is exposed to wave and current in addition to the platform motion during its installation inside well. In this article, we assumed a semi-submersible platform, which the first order motion was calculated using WAMIT. The platform motion timeseries, current, wave data were used as input in the Orcaflex. We calculated the time-domain simulation assuming the surface casing string in hangoff condition. The results show that the current bends the casing resulting in a higher Von Mises stress on the top part . In the other hand, the wave has effect only at sea surface resulting in a clear peak. Further, the lower end of the string has a peak of Von Mises stress because the axial tension is reduced in this region what reduces the geometric stiffness and increases the bending stress.