Petrobras Experience On the Mooring of Conventional Shuttle Tankers to Dynamically Positioned FPSOs

The record-breaking Roneador Early Production System entered operation in January 1999 when the FPSO Seillean started production through a rigid riser of a subsea well in 1853m waters. It was foreseen that in the first four months of operation, a conventional shuttle tanker would offload the oil produced by Seillean. However, the mooring of a large tanker to a Dynamically Positioned vessel, like Seillean, represented an enormous challenge. The major problem was the possibility of the shuttle tanker pulling the FPSO out of position during offloading operations causing an undesirable disconnection from the subsea well. In order to avoid this, it would be necessary to keep the tension in the mooring hawser below some pre-defined limits. First, some studies were performed to predict the maximum tensions in the hawser, using real data acquired from similar installations in Campos Basin. Then, when Seillean arrived at the location, some tests were carried out with the shuttle tanker moored to it, before starting production. These dummy runs were monitored and they allowed us to tune Seillean DP system and to define the best operation strategy for the shuttle. Finally, the first offloading operation using a conventional, non- DP shuttle moored to a DP FPSO was successfillly carried out in February 1999. This operation was also fully monitored and gave us more confidence to perform other 16 successful crude lifiings in Roncador. After that, as planned, a dedicated DP shuttle arrived in July 1999 to offload Seillean from the beginning of Brazilian winter onwards. This paper will focus on the studies and tests that were carried out to allow this pioneer operation. The results from the monitoring of the operations will be also presented.