The Instrumentation of the Conductor of a Subsea Well in the North Sea To Measure the Installed Conditions and Behavior Under Load
- G.W. King (Mobil North Sea Ltd.) | I.J. Soloman (Fugro-McClelland Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1995
- Document Type
- Journal Paper
- 265 - 270
- 1995. Society of Petroleum Engineers
- 4.5 Offshore Facilities and Subsea Systems, 4.5.5 Installation Equipment and Techniques, 1.14 Casing and Cementing, 1.6 Drilling Operations, 4.3.4 Scale, 1.10 Drilling Equipment, 1.7 Pressure Management, 4.5.10 Remotely Operated Vehicles, 4.2.4 Risers, 4.1.5 Processing Equipment, 1.14.1 Casing Design, 4.5.7 Controls and Umbilicals, 1.3.2 Subsea Wellheads
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The conductor design for subsea wells has not been studied to the same extent as the design of the subsequent casing strings. Models have been developed that incorporate riser and pile foundation analysis techniques to overcome this shortcoming. However, the models are dependent on a number of assumptions about the installed conditions, applied load, and resultant behavior, 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, we initiated a project to install sufficient instrumentation on the conductor of a subsea well, and 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 the results have been interpreted.
The critical importance of the conductor to the structural integrity of a subsea well has long been recognized. 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, along with the static loads imposed by the subsea equipment. The potential for catastrophic conductor failure has also been confirmed, and failure can occur from an excessive single load or from the cumulative "fatigue" 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 that combine riser analysis and soil/pile interaction analyses to simulate the loading on a conductor. 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 that typically need to be considered include soil stiffness, cement height, hole diameter, and environmental loads (Fig. 1).
A significant weakness of the analytical models is the absence of any field data against which they can be validated. For inner-string casing design, the applied loads and installed conditions are reasonably well understood; conductor design has relied on assumptions of effective cement height and load-transfer mechanics. Therefore, we decided to install instrumentation on a conductor for a North Sea well to measure the installed conditions and behavior under load. The well would be a typical North Sea well with a standard wellhead system and casing scheme.
Objectives of the Conductor Instrumentation Project
The following are the primary objectives of the instrumented conductor project (ICP).
1. To record sufficient data on the installed conditions and response of the conductor to calibrate the analytical model analyses.
2. To validate the assumptions of the model.
3. To assess the adequacy of the conductor design.
The data acquisition focused on three areas: the installed conditions, the applied loads, and the conductor response.
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