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

Abstract 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 transfer 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 and into the soil. In cases where the load exerted on the soil and cement exceeds the capacity, the soil around the conductor fails. Further can the cement filling the cavity between the conductor and the soil crack and consequently lose its intended function. Support degradation 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 (NCS) have been monitored using this SWIM service. As a part of the SWIM service, 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. An introduction to these integrity parameters will be given together with a 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. Finally, statistics on some core metadata such as water depth, region, and well type will be summarized and discussed.