NOV CTES - Zeta - Riser Monitoring & Safety System

The Zeta Safety System consists of an advanced job design and a real-time monitoring gauge for well intervention operations. The system utilizes a proprietary 3D finite element analysis (FEA) model in combination with highly accurate measurements from fiber optic gauges. This approach enables accurate modeling of changing stress levels across the entire riser/wellhead lubricator intervention stack. The system can be used for pre-job modeling to optimize and verify the safety margin of the job design. It can also be used in a real-time mode in the field, to monitor and issue a warning when stresses are approaching unsafe limits.

Pre-Job Modeling

Probability of exceeding pre-set safety limits
during the operation
Need for additional intervention stack supports
and their location
Stress changes as a result of stack loading changes
Maximum stress location
Weight required to buckle the stack
Stack vibration frequency
Optimized rig-up configuration

Field Monitoring

Monitor intervention stack stress levels
Impact of changing surface, downhole, and/or offshore field conditions
Suspend operations if maximum stresses approach unsafe limits
Resume safe operations following remediation
of problem

WHY (ZETA) IS NEEDED

Zeta was developed due to potential safety concerns associated with the use of longer and more complex intervention stacks. These tall stacks are more susceptible to bending excitation forces from crane, production riser, and platform movements. At present, a judgment call (based on little or no hard data) is made regarding how much lubricator sway or wellhead movement is acceptable, when to add supports, or even when to halt operations due to safety concerns. Motion associated with TLP’s and Spars only compound this problem. The Zeta Safety System eliminates guesswork and provides a tool for optimal rig-up configuration.

EQUIPMENT

The Zeta Safety System is comprised of two basic components, the Zeta Model
and the Zeta Gauge.

(Zeta) Gauge

2’ lubricator spool built to API requirements
Uses fiber-optic strain gauges to measure
- Axial force
- Internal pressure
- Bending moment (left and right)
- Bending moment (forward and backward)
Calculates Von Mises stress in the gauge
Displays force, pressure, moment and stress values
Communications with the Model software in real-time
No electricity to the gauge - no certification issues
Fiber optic gauges are very stable - remains calibrated

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Zeta Model

Used during job design to ensure safe stack design
Models entire wellhead/lubricator stack with its supports and applied loads
Calculates:
- Displacement (motion) of the stack
- Von Mises stresses in the stack components
- Vibration frequency of the stack
- String weight required to buckle or yield the stack
- Static or dynamic loading in the guy wires or support structure
Real-time input from the Gauge can be used to determine maximum stresses in the stack
Warning when pre-set stress levels are exceeded

For detailed information on the Zeta Model, click here.

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In the Zeta screen capture above,
the blue curve represents stress in the intervention stack.

For additional information, the following are available for download:

Literature

Zeta Brochure

Technical Papers, Articles & White Papers

SPE 89502 Finite Element Analysis of Coiled Tubing Forces
SPE 89515 IRISS - Intervention Riser Integrity and Safety System
Zeta Model Validation (analytical solution vs. the Zeta Model output)

Software

Zeta Model Software (fully functional demo software)