Although thankfully not a common occurrence, when a BOP stack is dropped, it is most often a catastrophe. With the understanding of the causes of dropped stacks provided in this paper, one will be able to identify specific steps to minimize the likelihood of this type of failure on future projects in any floating drilling operation.


Every dropped BOP stack is a significant event for all parties involved in the drilling program. In many cases, the retrieval process and subsequent equipment review to identify and rectify damage results in significant delays. The severity is further exacerbated if the dropped object lands on production equipment in the case of development drilling. As a result, a major operator conducted a study for a world class development project to enable them to identify and mitigate prospective dropped objects, with the primary emphasis on dropped BOPs. This paper will:

  • categorize causes of documented dropped stacks and significant near misses,

  • identify root causes within each category, and

  • recommend steps that can be taken to reduce the likelihood of reoccurrences.

Data Sources

Unfortunately from a quality enhancement perspective, difficulties in the drilling industry are neither well documented nor widely circulated. This makes gathering information difficult. Nevertheless, the 219 cumulative years of industry experience of eight WEST staff was pooled to identify both incidents and near misses. To the extent possible, contact was made with other individuals who had personal involvement with the incident under investigation. Because this methodology in general is subject to the recollections of the parties involved rather than documented analyses, one might not be surprised to learn that some of the details could be somewhat inaccurate. Nevertheless, the author believes that the major issues surrounding significant events such as dropped stacks are retained with a high degree of accuracy, thus supporting the validity of the overall conclusions.

Definitions and Acronyms

The data analysis focused on grouping incidents by a) systems that were the root or major cause of failure, and b) the cause of that failure. Definitions of each of the categories and causes are stated below.

  • Riser system - any part of the riser string, from the telescopic joint to the flex or ball joint, inclusive.

  • Accidental unlatches - incidents that caused an accidental unlatch of the riser connector.

  • Topside systems - any rig system, other than parts of the aforementioned riser system, that remain dry.

  • Well - problems with wells. Rather than create another category, one incident whose major cause was weather was included in this already small group.

This content is only available via PDF.
You can access this article if you purchase or spend a download.