Through collaboration among TOTAL, TRANSOCEAN and 3DENT TECHNOLOGY, an initiative was launched to investigate the capabilities of the GSF Galaxy I jackup to perform a rig move in waves with periods greater than 6 seconds. The objective was to improve the rig move performance by reducing waiting on weather time.
GSF Galaxy I, is a Friede & Goldman-designed Mod VI harsh environment jackup. The generic Class-approved wave conditions for emplacement, preloading and leg extraction are simply stated in the operating manual as 6-foot wave height at 6-second period.
Consulting for TRANSOCEAN, 3DENT started the study by conducting so-called "Going on Location" studies in regular waves and random waves to establish permissible wave heights as a function of period. 3DENT later developed a methodology for analyzing the coming off location and preloading at large draft conditions. This paper discusses the various analyses, techniques and results of the studies conducted by 3DENT in the development of a user-friendly response assessment program to assist TRANSOCEAN rig personnel in the decision to carry out Going on Location, Preloading and Coming off Location operations with known information about the environmental conditions.
The response and therefore the limiting wave heights under which the various operations can safely be undertaken, requires a clear definition of the waves. Utilization of a wave radar, providing much-improved information on the waves when compared to either estimates by human observers or weather forecasts, was key to providing a verified and reliable input.
The response assessment program was successfully used while moving the GSF Galaxy I from the north to the south side of the TOTAL Elgin platform, saving 10 days of waiting on weather over a 15-day rig move. This application demonstrated it is possible to safely increase the environmental envelope for rig moving operations.