Subsea System Engineering and Operations Consulting

Posts tagged Riser analysis GRA

Global Riser Analysis – “Creating a Bridge between Riser Analyst and Operational Consultant”

Key Messages of Blog:

  • Providing Operational input (**)  to support the analyst create the GRA (Global Riser Analysis)  model is essential and can result in lower cost , and improved quality of results.
  • System boundary conditions between riser /landing string need to be defined early to ensure GRA analysis is accuracy
  • Understanding Subsea Equipment functional and structural capacities factor into GRA and adjustments to operability ranges for various uncontrolled events like weather , sea state and currents.
  • End user should have a quality program to ensure that GRA model accurately depicts the “system” which includes the MODU (Mobile Offshore Drilling Unit), Riser / landing string, and compensation systems.
  • Assisting the riser analyst understand the significant aspects of the GRA model and ensure that boundary conditions and constraints are identified working as a team will deliver the best overall result.

Open water deployed Completion and Work-over Riser systems (CWOR)  and Specialized Landing strings with SSTT (Subsea Test Trees) run inside Marine Drilling riser systems are two modes to establish bore access to a subsea production tree.   Deployment is either from a MODU or MSV (Multi-Service Vessel) with motion compensation hoisting systems to decouple vessel heave from the riser or landing string.

Riser analyst are often contracted to provide a global riser or landing string analysis which defines allowable operational envelopes for the completion and intervention system.  A typical challenge is many of the riser analyst do not have full understanding of the offshore boundary conditions and constraints and need technical / operational input from operator / consultant (eg DeepMar).

Creating a global model of the subsea equipment, wellhead , Subsea tree and riser  with appropriate stiffness factors at each transition is vital to ensure screening results are estimated accurately.   Additionally, building an interface model with the vessel compensation system to ensure stiffness of compensation during heave, stroke limits , and offset limits are established to ensure riser does not contact MODU /MSV hull all are contributing factors in the GRA analysis.

Typically the end user (eg Operator) has to provide oversight to ensure appropriate boundary conditions  (e.g.  accurate compensation stiffness factors, soil stiffness factors, specific to the well)   are key factors in the analysis process.   Offering practical and operational guidance early in the build of the GRA model can be invaluable and result in an overall lower cost solution. Training and mentoring analyst to improve operational boundary condition understanding  is essential to creating an analytical tool with value.

** DeepMar has provided riser / landing string Design and Operational Assurance service on behalf of major operators to improve safety and operability.