Tools and Techniques for the Selection and Design of Safe Deepwater Riser Systems for Mobile Offshore Drilling Units

Abstract

The deepwater drilling industry has been rocked by the tragic Deepwater Horizon event in the Gulf of Mexico. The incident identified a number of possible failings by operator, service contractors and the regulator which combined to lead to the ultimate results which were evident in mid 2010. This paper will assess the options available to the deepwater drilling industry in assessing the risk of various riser and BOP configurations for drilling and completing deepwater wells in moderate metocean environments. The paper will address two different systems:1. A classic subsea BOP stack configuration, 2. A surface BOP stack with a subsea isolation device (SID). Both of these configurations have merits depending upon a number of factors which include rig availability and schedule, project economics, riser integrity, BOP configuration, geological issues and, most importantly, the hazard and risks associated with each concept. This paper will identify the various technical analyses and risk analysis techniques that must be undertaken to assure the operator of the system is comfortable with each system. These include riser analysis, rig mooring and station keeping analyses, system HAZIDs and HAZOPs, and more. The idea of the paper is to provide the operator and drilling contractor with a 'road map' which will allow them to navigate their way through the various issues to be addressed. This road map will start with the concept stage (rig contracting early well planning) where issues such as project economics, rig availability and risk tolerance will provide input into the overall decision making process. The paper will next address the preliminary and detailed design stages where issues surrounding metocean criteria, rig characteristics and rig configuration and geological conditions will play a part in the overall input. The paper will describe how a project team would approach the issues. Finally as the project moves to the implementation stage the paper will describe the techniques for final assurance that the concept can be managed in the implementation stage.

Subsea blowout preventer (BOP): Design, reliability, testing, deployment, and operation and maintenance challenges

“…[14] Use of qualitative risk assessment (QRA) to prioritize areas of greater reliability concern [15] Evaluating failure statistics and testing time consumption for 83 GOM wells in 400-2000m water depths [16] Positive effects of inspection and testing for high-pressure high-temperature (HPHT) BOPs [17] Evaluation of downtime caused by BOP failures and testing [18] DW BOP reliability and failure rate evaluation. BOP failure calculations based on drilling cycle [19] Reliability analysis across different activity phases and operating conditions for subsystems [20] BOP control system reliability relative to maintenance goals [21] Risk management of surface blowout preventers (SBOPs) in DW and comparison with SSBOPs [22] New hybrid electro-hydraulic control system development for DW BOP applications [23] Limitations in accumulator design [24] Comparing risks of different configurations on DP rigs [25] Design challenges and solutions for BOPs (ram preventer in particular) [26] Experience with SBOP and its advantages [27] Automatic monitoring of BOP state to improve maintenance Post-Macondo [12] Forensic investigation of the Macondo BOP [28] Detailed DW SSBOP reliability evaluation and kick data for 259 wells in the GOM OCS [29] Risk assessment options for operating different BOP configurations (SSBOP and SBOP with SID) [30] Risk analysis of drilling in DW with considerations to leakage in ram preventer in particular [31] Condition and performance monitoring of a pressure regulator employed on deepwater BOPs…”