Risk-Based Case Study of Floating Facility Drilling Riser Design Concepts in Deepwater Gulf of Mexico

Abstract

Regulatory changes in recent years have shown more stringent drilling riser inspection and maintenance criteria with the objective of minimizing Health, Safety and Environmental (HSE) risks, as evident with the December 2009 draft MMS NTL on integrity issues surrounding dedicated drilling risers used on floating production facilities. Additionally, the catastrophic Macondo incident has brought to the forefront the risks associated with traditional offshore drilling, which lends an added emphasis to clear assessment and management of HSE risks for all drilling and production risers. This paper presents the methodology proposed for the risk-based comparison of different production and drilling riser system configurations. The methodology is recommended for the concept selection phase of any new drilling riser development to enable a side-by-side comparison of the critical risks within each system. This risk approach facilitates the identification of required mitigation measures to reduce risks to As Low As Reasonably Practical (ALARP). In addition an Integrity Management Strategy is proposed and recommended mitigation measures are compiled in different categories: design, inspection and operating measures. An action tracking database then assigns the implementation of mitigation measures to appropriate development phases (including the operations phase) to allow traceability and ensure risks remain ALARP. The authors will demonstrate the implementation of this methodology for three drilling riser configurations: a monobore drilling riser (base case), a drilling riser with an insert casing riser system, and a monobore drilling riser with a Subsea Isolation Device (SID) system. The case study will consider a deepwater, normally pressured Gulf of Mexico field, taking into account the following scenarios: running the drilling riser; running of drill string and casing; drilling, before and in the hydrocarbon payzone; simultaneous operations (SIMOPs); and other vessel-related activities. Following typical practices for deepwater developments in the Gulf of Mexico, a surface blowout preventer (SBOP) is assumed to be employed for managing well control. The insert riser system and the SID system will be considered by comparison to the monobore system to facilitate the presentation of each option. The most critical risks associated with all three drilling riser systems will be determined in a clear and transparent manner, along with the measures that are required to mitigate these risks to ALARP.