Restriction Diagram: Realibility Study of Drilling Ships with Dynamic Positioning System

The Restriction Diagram is a tool that delimits the minimum distance between a dynamic positioning (DP) drilling rig and surface or subsea obstacles (Platforms, anchor lines, subsea equipment) for safe operation. These diagrams are used for risk analysis and well operations restricting the operation of some rigs in some locations or avoiding very large drilling operations next to each other. They are also used as one of the parameters to determine the best position of the platform in relation to the wells, impacting any subsea layout of a new field development. The analysis of restriction diagrams are essential for risk assessment involving drilling rigs. It is important to improve the quality and robustness of the methodology presented due to safety distances. This proposal of the new model of the Restriction Diagram aims to support the risk analysis of Drilling Rigs operations including the probability of drilling rigs failure, recovery times and hydrodynamic probabilistic modeling. There is integration between all the parameters involved in the process and the propagation of its uncertainties. The reliability analysis of the dynamic positioning drilling rigs used an extensive database of incident logs, from which was extracted the occurrences of total loss of propulsive capacity of the drilling rigs that resulted in a drift-off. It was considered the operating time and failures that have occurred since 2010, as well as the drilling rig recovery time. The drift-off analysis are represented by means of hydrodynamic modeling coupled to a probabilistic simulator. This risk-based analysis from reliability and environmental conditions will give the chance of collision with obstacles for drilling operations or well intervention. This paper presents a risk assessment approach according to the new emphases that are beginning to be considered by regulatory authorities such as the Petroleum Safety Authority (PSA) in Norway, considering the integration between decision processes and uncertainty analysis.