Definition of Well Operating Envelope for Floating Rig During Well Testing Operations

Abstract

The purpose of this document is the definition of the operational areas for floating rig during well testing operations, depending on the depth of water and meteorological conditions. The main problem for a floating system is the station keeping. In order to operate, in fact, the rig must be located around the well. Considering the Rig-Riser-BOP system, the latter is fixed to the bottom, while the rig is subject to the forces of the wind, waves and currents that cause it to move from the vertical of the well. As the rig moves, the riser tilts and lowers relative to sea level. At the same time, the telescopic joint and the tensioners extend up to their maximum available. Once these limits have been exceeded, the riser-rig connection is no longer guaranteed because either the telescopic joint goes out of travel, or the tension cables break. In the Well Testing phase, this situation is aggravated by the presence of the string inside the riser. Its position is fixed; therefore, a lowering of the riser corresponds to a lowering of the string at the end of which is the flowhead. It must be ensured that the lowering of the riser is less than the maximum distance flowhead – rig floor. Therefore, while the operational limits of a rig are dictated by the telescopic joint and by the tensioners, the operational limits for the test phase are dictated by the flowhead-rig floor distance. In order to avoid reaching these limits and endangering the safety of the system, areas are defined in which it is possible to operate, carry out the test, or areas where it is necessary to disconnect the riser and make the system safe.