Session: 04-02-02 Rigid Risers II

Paper Number: 81117

81117 - Conductor Instability – Experience From 10 Years of Monitoring Drilling Operations on Subsea Wells in Harsh Environments 

Subsea production and exploration wells are subjected to loads from the drilling riser and subsea BOP.  Over time BOPs have grown in size and weight resulting in larger wellhead loads.  The main task of a subsea conductor is to act as a foundation for the transfer of these loads into the seabed.  The bending loads applied on the wellhead will be transferred into the conductor, which again will transfer the loads through the cement into the soil. 

In cases where the load exerted on the soil and cement exceeds the capacity, the soil around the conductor fails and the cement filling the cavity between the conductor and the soil can crack and lose its intended function as a consequence.  Degradation of the support of the upper sections of the conductor reduces the conductor's ability to support the well. More load will have to be taken by the conductor and casing structure.

4subsea has delivered the Subsea Wellhead Integrity Monitoring (SWIM) service for operations on subsea wells for over 10 years.  Sensors monitoring the motion and loads near the subsea wellhead have been mounted on more than 300 drilling campaigns.  For the last couple of years, more than 70% of the drilling operations with semi-submersible drilling rigs on the Norwegian Continental Shelf have been monitored using this SWIM service.  As a part of the SWIM system, integrity parameters showing whether the conductor gives the intended amount of support are calculated.  Loss of conductor support during drilling operations has been observed in several of these campaigns.  A brief introduction of these integrity parameters will be presented together with a brief discussion on the integrity issues that can be detected using these parameters. 

The main purpose of this paper is to summarize the observations of conductor instability over the last 10 years.  Examples of monitoring results showing how the instability issues were detected will be presented. Examples of actions taken to react to conductor instability will also be discussed.  The different instability occurrences will be classified by severity.  Finally, statistics on some core metadata such as water depth, rig type, region, and soil conditions will be summarized and discussed. One of the main findings is that the number of conductor instability issues over the last couple of years might be an indication of weaknesses in the up-front foundation design methodology.

Presenting Author: Håkon Molven 4Subsea

Authors:

Håkon Molven 4subsea
Per Kristian Pöcher 4Subsea
Vegard Martinsen 4Subsea
Harald Holden 4Subsea