The conductor design for subsea wells has not been studied to the same extent as the design of tie subsequent casing strings. To overcome this, models have been developed which Incorporate riser and pile foundation analysis techniques, however the models rue dependent on a number of assumptions on the installed conditions, applied load, and resultant behaviour which have not all been fully validated. There have also been cases where the structural failure of the conductor has resulted in the loss of a well.
To enhance the understanding of conductor design, a project was initiated to install sufficient instrumentation on the conductor of a subsea well, together with a data acquisition system, to enable the recording of the significant conductor parameters for comparison with model predictions. This paper describes: the objectives of the measurement program; the design and testing of the instrumentation systems; the offshore installation and operation; the results obtained ;and how they have been interpreted.
The critical importance of the conductor to the structural integrity of a subsea well has long been recognizedl. Previous work has emphasized the need to transfer the loads applied to the wellhead to the conductor, and out through the cement into the soil. The loads are the result of the environmental forces of wind, waves and currents acting on the rig and riser, together with the static loads imposed by the subsea equipment. The potential for catastrophic conductor failure has also been confirmed2, and failure can occur from an excessive single load or from the cumulative â??fatigueâ?? damage of a large number of smaller cyclic loads.
The need to include conductor design in the design of a well has resulted in the development of analysis models which combine riser analysis and soil-pile interaction analyses to simulate the loading on a conductor3. Such models are invaluable for sensitivity analyses of a conductor to evaluate the effect of a range of parameters when precise values are not available. The parameters which typically need to be considered include: soil stiffness; cement height; hole diameter and environmental loads (figure 1).
A significant weakness of the analytical models is the absence of any field data against which hey can be validated. For inner string casing design the applied loads and installed conditions am reasonably well understood, conductor design has relied on assumptions of effective cement height and load transfer mechanics. Therefore it was decided to instrument a conductor for a North Sea well to measure the installed conditions and behaviour under load. The well would be a typical North Sea well using a standard well head system and casing scheme.
The primary objectives of the Instrumented Conductor Project (ICP) were:
to record sufficient data on the installed conditions and response of the conductor to calibrate the analytical model analyses;
