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Riser Analysis

We specialize in riser analysis of the overall riser system in combination with a detailed model of the top side equipment, non-standard riser system or optimization of riser system configuration. Key objectives are operating conditions and feasibility of critical components. We also analyze the riser tensioning systems capability to lift the Riser Stack and LMRP of the BOP in a controlled motion during a disconnect sequence. A detailed hydraulic model of the tensioning system and mud flow is made specific for each project.

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Global Riser Analysis

The Global Riser Analysis describes the operational limits for offshore operations in different environmental loads. These limits are found according to criteria described in API RP 16Q , ISO 13624 or similar recommended practice / standards. The global analysis is a FEA of the complete riser structure, and a dynamical riser model is built based on the actual riser joints for offshore operations, like Telescopic Joint, Upper/Lower Flex Joint, Bare Riser Joints, Riser Joints with buoyancy elements, LMRP and BOP.

Cases for the Riser Analysis are:

-Connected Drilling mode
-Connected Non-Drilling mode
-Deployment & Retrieval of BOP, supported in Gimbal/Spider and Derrick
-Hang-Off at Gimbal/Spider

Typical input data required for an analysis would be riser joints, riser configuration, vessel configuration/layout of tensioner, drillfloor and relevant equipment in derrick, vessel RAO data and environmental data for the offshore location.

The software used for the Riser Analysis will be Orcaflex. OrcaFlex (www.orcina.com) is the world's leading software package for the design and analysis of a wide range of marine systems, including all types of:

-Riser systems: SCRs, TTRs, hybrids, flexibles, umbilicals, hoses.
-Mooring systems: spread, turret, SPM, jetty, etc.
-Installation planning with capabilities across the full range of scenarios.
-Towed systems: bundle dynamics, seismic arrays, towed bodies, etc.
-Defence, marine renewables, seabed stability and many other types of system.
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Deployment and Retrieval Analysis

Several deployment and retrieval stages for the riser system are analysed for stresses and physical clearances. The riser is analysed for hangoff in drillfloor and the lifting equipment, typical a Top Drive in a Derrick structure. The images here show the Riser Running Tool delivered by CDS.

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Riser Disconnect - Recoil Analysis

CDS performs disconnect and recoil analysis to show the riser tensioning systems capability to lift the Riser Stack with the LMRP of the BOP in a controlled motion during a disconnect. The output is allowable riser tension settings and closing curves for the Riser Tensioners valves such that the LMRP do not fall back on the BOP/Wellhead and the Telescopic Joint is not collapsed at high speed or jump out of the Tensioner Ring.

The analysis is performed by 3D multi-body system model with full 6 degre of freedom for critical parts like the LMRP, Tensioner Ring and Telescopic Joint. Multi-discipline simulation is used for a detailed hydraulic model of pressure losses in tensioning system and discharge of mud column in riser.

BOP Landing

The landing of the BOP and the complete riser stack on the wellhead is a critical operation where several systems are involved. The load of the riser stack is typical divided on the riser tensioning system, the top compensator, an active heave compensator and also the drawwork that lowers the riser stack.

The BOP Landing performance at different evironmental loads are analysed in a multi-discipline simulation of the 3D mechanical system, hydraulic system for tensioners and compensators, and the control system for the AHC.

Hard and Soft Hangoff

CDS performs dynamical analyses under storm environment and annual wave scattering where a disconnected riser stack is hung off in the Spider or supported by the tensioning system. The criteria is to have allowable stresses and clearances in a storm.

CDS also finds operational limits for a vessel/rig transit operation with supported riser stack for cases where other wells are nearby.

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Riser Configuration Optimization

CDS builds a modular and easy configurational set-up for the riser analysis model. Several riser model configurations are picked from a library and simulated in batches for finding optimized configuration data for riser stack-up, locations, environmental loads, vessels and also vessel layouts.