viv monitoring enhancing the safety of drilling operations in high current environments

www.pulse-monitoring.com

VIV Monitoring: enhancing the safety of

drilling operations in high

current environments

August 2014


Agenda

• Environmental loading

• Vortex induced vibration

• GOM loop currents

• Riser monitoring

• Case study: VIV monitoring


Vortex induced vibration

• Caused by strong, steady currents when

vortices shed by current flow around the riser

matches a natural frequency of the system,

resulting in amplified lateral motions (resonance)

of the riser;

• Generally the governing environmental load in

water depths exceeding 250m;

• Can cause excessive motion of the riser.

Overview


Industry issues

Vortex Induced Vibration

BOP stack excitation

Seabed

BOP

LMRP

Wellhead

36” / 20" pipe

38” / 36"pipe

Conductor_____

Connector

Drilling Riser BOP Stack Excitation

• High amplitude movements in

riser system can lead to:

• Accelerated fatigue;

• System degeneration;

• Riser failure.

BOP stack natural frequency

excitation has been observed

during relatively high-speed loop

currents;

This can result in high

accumulated fatigue damage at

the fatigue critical conductor

connector below the mudline.


VIV in the Gulf of Mexico

• The loop current in the deep water Gulf of Mexico is

the primary driver of high speed ocean currents;

• Excessive loop currents have been observed a

number of times over the past decade, causing

drilling operations to be halted and risers to be

retrieved;

• Some of these loop currents have led to current

speeds of up to 4 knots. Historically, current speeds

of over 1.5 knots have been seen as problematic;

• In the strongest currents it may not even be

possible to unlatch the BOP and retrieve the riser

due to issues with excessive riser motion during

hang-off.

Effects of the loop current



• Data loggers using a combination of accelerometers and

angular rate sensors located at predefined strategic

locations along the length of the riser, on the BOP stack and

on the vessel;

• Data loggers along the riser measure riser motion to identify

mode shape;

• Strain sensors can also used for localized strain

measurements at fatigue critical locations:

• Bonded strain gauges;

• Subsea strain sensors;

• Dynamic curvature sensors.

Riser Monitoring


Standalone Acoustic Hardwired Eexd

Vortex Induced VibrationData logger technology

There are a number of data logger options available, the choice of which will depend on monitoring parameters,

logging location and communication preference;

Hardwired and acoustic communication provides real time operational data to the rig, allowing for improved

decision making based on accurate information. .

Off-the-shelf rental systems are available at short lead time


Logger 56

x/L= 0.000

Logger 55

x/L= 0.112

Logger 54

x/L= 0.160

Logger 53

x/L= 0.208

Logger 52

x/L= 0.257

Logger 51

x/L= 0.305

Logger 50

x/L= 1.000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

0.10.20.30.40.5

Frequency (Hz)

Accele

ration

Am

plit

ude (

m/s

2)

Schiehallion Event 91 - Magnitude of Peak Response vs. Frequency

Accelera

tion

Amplitud

e (m/s2)Logger 56

x/L= 0.000

Logger 55

x/L= 0.112

Logger 54

x/L= 0.160

Logger 53

x/L= 0.208

Logger 52

x/L= 0.257

Logger 51

x/L= 0.305

Logger 50

x/L= 1.000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

0.10.20.30.40.5

Frequency (Hz)

Accele

ration

Am

plit

ude (

m/s

2)


Accelera

tion

Amplitud

e (m/s2)Logger 56

x/L= 0.000

Logger 55

x/L= 0.112

Logger 54

x/L= 0.160

Logger 53

x/L= 0.208

Logger 52

x/L= 0.257

Logger 51

x/L= 0.305

Logger 50

x/L= 1.000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

0.10.20.30.40.5

Frequency (Hz)

Accele

ration

Am

plit

ude (

m/s

2)


Accelera

tion

Amplitud

e (m/s2)

INTEGRIpods

Riser Monitoring


Data loggers installed along the riser allow

visualisation of riser mode shape;

Using a placement strategy based on preliminary

analysis, these motion loggers do not have to be

located along the entire length of the riser. Instead,

a strategic clustering of loggers at one or both

ends of the riser can still allow prediction of global

riser response with the required accuracy



• Using an online monitoring system provides

real time data on the rig allowing operational

decisions to be based on observed riser

behavior;

• Post processing is conducted on the measured

data in time and frequency domain, allowing

for the source of motions to be identified;

• Amplitude and frequency of stress cycles is

used to obtain fatigue calculation;

• Data also allows for calibration of analysis

model.

Data analysis

Real time data displayed on the rig


Case Study: VIV monitoring in the Gulf of Mexico


Deep Water VIV monitoring

• Drilling campaign in Gulf of Mexico

• 2000m water depth using 6th

Generation semisub

• Analysis showed conductor fatigue life

of just 8 days

• Conductor top weld shown as fatigue

critical location

• Standalone monitoring requested to

record actual motion responses of the

system

Project Background


Monitoring System


12

• Eexd-rated INTEGRIpod on vessel

to measure vessel motion

• 10 standalone INTEGRIpods along

riser to measure riser motion

• 2 standalone INTEGRIpods on BOP

to measure angular rate of BOP/

LMRP

• Subsea data loggers installed using

magnetic interfaces


ROV INTEGRIpod installation


13



• Monitoring data used to determine actual conductor fatigue incurred during operation;

• Data showed acceleration threshold for conductor top weld not exceeded;

• None of VIV events resulted in above-threshold riser fatigue damage;

• Client did not have to undertake detailed fatigue analysis of drilling campaign.

Results & Lessons Learned

14


Summary

VIV issues and solutions:

• Environmental loading can cause fatigue

damage to subsea risers, wellheads and

conductors;

• In the deep water Gulf of Mexico, the loop

current can lead to vortex induced vibration

and thus excessive loading in the riser

system;

• Structural monitoring systems can be

installed to provide a detailed

understanding of asset behavior. Real-time

data can provide instant warning of

excessive motion.

viv monitoring enhancing the safety of drilling operations in high current environments

Technology