Subsea power cables are crucial for transmitting electrical power between offshore installations, islands, and onshore infrastructure. The demand for these cables has surged with the expansion of offshore wind farms. Despite mechanisation, divers are still needed for tasks such as installation, inspection, and remedial work, facing hazards like entanglement, equipment damage, and those to the environment. Therefore, analyzing accidents in diving operations during subsea cable installation is essential to develop safety measures that protect divers and ensure successful installations. This document reports an analysis of the hazards and accident events linked to diving operations during subsea cable installation. Few risk assessments of these operations have been made publicly available.
Various methods can be used to analyze diving accidents, but this document reports on the use of the Accident Anatomy (AA) method. The AA method combines fault trees and cause-consequence diagrams to map accident causes and consequences. In the AA method, evidence-based (post-accident) analysis is used jointly with predictive analysis to identify deviations from normal conditions that could lead to accidents.
To exhaust the identification of hazards, the AA method is additionally powered by an error mode classification checklist, which classifies errors that produce similar effects on a system. Analysts used this checklist to identify hazards for each basic diving operation task identified.
As a data source, 163 documents were analyzed, including accident records, regulations, manuals, and scientific papers. Basic tasks associated with diving operations are identified, along with hazards for each task. Predictive analysis identifies potential events and unwanted consequences when normal conditions (specified in safety procedures and specifications) deviate. The unwanted consequences that were found include delays, technical problems, injuries, and fatalities. Ultimately, safety measures are identified for each basic task to reduce the effects of hazards.
The upstream offshore multi-phase well-pipeline-riser installations are facing huge challenges related to slugging flow: An unstable flow regime where the flow rates, pressures and temperatures oscillate in the multi-phase pipelines. One typical severe slug is induced by vertical wells or risers causing the pressure to build up and hence originates the oscillating pressure and flow. There exist many negative consequences related to the severe slugging flow and thus lots of investments and effort have been put into reducing or completely eliminating the severe slug. This paper reviews in detail the state-of-the-art related to analysis, detection, dynamical modeling and elimination of the slug within the offshore oil & gas Exploration and Production (E&P) processes. Modeling of slugging flow has been used to investigate the slug characteristics and for design of anti-slug control as well, however most models require specific facility and operating data which, unfortunately, often is not available from most offshore installations. Anti-slug control has been investigated for several decades in the oil & gas industry, but many of these existing methods suffer the consequent risk of simultaneously reducing the oil & gas production. This paper concludes that slug is a well defined phenomenon, but even though it has been investigated for several decades the current anti-slug control methods still have problems related to robustness. It is predicted that slug-induced challenges will be even more severe as a consequence of the longer vertical risers caused by deep-water E&P in the future.