Transcript Deepwater Meets the Shelf

Deepwater Meets The
Shelf.
Paul Stevenson
Regional Manager
Fugro Structural Monitoring
September 9, 2009
Deepwater Meets The Shelf
Production from Deepwater Developments
rely on the existing older infrastructure on
the Shelf to come to Market.
 Expanding development in deepwater will
inevitable put more strain on the existing
older infrastructure.

GOM Pipeline Routing
Safeguard Structural Integrity of Shelf
Platforms
There is a growing need to further
safeguard the structural integrity of the
shelf platforms.
 This is done by regular inspection on
typically 5 year interval but can be longer.

Current GOM Inspection Approach

Majority of platforms are on a five year
underwater inspection interval alternating
 Level
II - primarily general visual inspection (GVI)
 Level III - GVI and close visual inspection (selected
nodes and some FMD Flooded Member Detection)


MMS administers this process following Federal
law 30 CFR 250.901 which generally adheres
to API RP 2A guidelines
Underwater inspection of platforms is primarily
performed by divers
What Happens to Production When a
Hurricane Comes Through The GOM

Similarly an inspection process is enforced after
an event such as a hurricane.
 Production is shut-in (stopped at source)
 Hurricane Passes
 Topside Visual inspection is carried out
 Assessment done to establish what further
level of
inspection is required, and carried out.

Pursuant to 30 CFR 250.919 which generally adheres to API
RP 2A guidelines and more recently extracts from API BUL
2HINS
 Production
is started if deemed safe to do so.
Which Platforms Are Selected to be Inspected
The Post Hurricane Inspections
Approximately 3400 platform
Inspections were required and
has taken many years to
complete
Why so long?
Mainly Due to Lack of Resources After
Hurricanes
GOM Workboat DayRates
WorkBoat Survey of 34 Offshore Vessel Supply Companies
4
100
Utilization Maxed
Normalized US $ / Day
Katrina Shut-in
Hurricane Katrina/Hurricane Rita/Hurricane
Wilma Shut-in
3
AHTS Quadrupled in
Price Since Nov 04
Average Price 15 to 60
$K
Hurricane Dennis
Shut-in
2.5
2
90
85
80
Supply and Crew Boats
Doubled in Price Since Nov
04
75
Average cost 7 to 10 $K
1.5
1
20-Sep-04
95
% Fleet Utilization
3.5
70
9-Nov-04
29-Dec-04
17-Feb-05
8-Apr-05
28-May-05
17-Jul-05
5-Sep-05
25-Oct-05
14-Dec-05
AHTS Dayrate
200' Supply Boat Dayrate
125' Crew Boat Dayrate
AHTS Utilization
200' Supply Boat Utilization
125' Crew Boat Utilization
2-Feb-06
What Happened To Production
What Can we do to Ease The Inspection
Burden
World Trends to Inspection:




Move away from detailed weld inspection and towards
less invasive methods (e.g., FMD)
A stronger focus on the overall Structural integrity
Acceptance that some level of damage can be shown to
be permissible
Structural Integrity Response monitoring as an
alternative to subsea inspection
What is Structural Integrity Response
Monitoring
Structural Integrity Response Monitoring is considered to
be the process whereby:

Response characteristics of a structure are measured
(either continuously or at regular intervals)

With a view to comparing the measured characteristics
with a previously measured baseline or trend.
Structural Response Characteristics
Mode Shapes, Natural Frequencies
Offshore Fixed Jacket Structural Response
Characteristics
1 Torsional Mode
st
Sway Mode
Typical Acceleration Power Spectrum
0
10
-1
2nd Sway Mode
Power Spectral Density
10
Higher Order Modes
2nd Torsional Mode
Sway Mode
-2
10
Torsion Mode
-3
10
Dominant
Wave
Excitation
-4
10
0
0.5
1
Frequency (Hz)
1.5
How do we Assess the Structural Response
Characteristics

Sensors on structure
 For
an offshore fixed platform it can be
something as simple as a vibration
sensor
Acquire Structural dynamic data
 Perform Structural Analysis
 Compare results with model or Trend

The Basis to Structural Integrity
Monitoring
The frequency response of the structure is determined from the
stiffness and mass properties of the structure. In the over simplified
form:
f
1

2
k
M
•Single Degree of Freedom Oscillator
where k is the stiffness of the ‘spring’ returning the mass, M,
to its equilibrium position.
On a platform, k is a measure of both jacket and foundation
stiffness.
How Does Structural Response Monitoring
Work?

Change in stiffness leads to a detectable shift in
response frequency of the platform.

Structures loaded periodically by wave loading.
(Excitation force)

Accelerometers detect movement on topsides.
(response to excitation force)

PC collects and processes data to show
frequencies of dynamic response of structure.
Some Examples of Where Response
Measurements Are Used?

One of the oldest systems is installed on the CNR’s (formally
Chevron’s) Ninian Southern Platform in the North Sea in 1986.







The most recent Fugro OLM systems :
ExxonMobil Thames field (4 platforms)
Statoil’s Kvitbiorn Platform
Chevron’s Benguela Belize Compliant Tower offshore West Africa
(about to be commissioned).
ExxonMobil Thebaud Platform (Sable Island)
CNR’s East Espoir
Pemex AKAL H and C1 (includes shallow gas and seismic
monitoring)
Other OLM systems previously in the North Sea: Shell’s
Goldeneye, Tern A, BP’s Magnus, Forties Alpha and Bravo,
Total’s MCP01, Statoil’s Gulfaks, Oseberg A and C, 16/11 E
Fugro have performed over 200 of these measurements worldwide
Advanced Eigen Analysis
Combining the advanced computer structural modeling
with the advances in measurement technologies
Major Benefits of Response Measurements

To reduce periodic sub-sea structural inspection.
 Either by extending the time between regular inspection or by omission after
an event.

Instant detection of subsea structural failure after seismic event, storms,
hurricanes, impact etc
 Allow the operator to focus on damaged platforms.

Reduce the time the structure is at risk to a failed member.
 Hence reduce the probability of catastrophic failure.


Assess the effectiveness of a repair to platform
 Show that the platform stiffness has returned to an acceptable level

Tune Structural Model, for assessing effect of modifications and damage to the
structure.

Risk-based inspection methods can demonstrate the influence of the damage on
a structure.
Secondary Benefits
It can be used as an alarm system on
unmanned platforms in the event of a
collision with a vessel.
 Where marine growth is a problem the
system may show a significant change in
structural response.
 Ensuring no further degradation in
robustness during platform abandonment

Case Study of Subsea Structural Failure
4-legged Jacket
 100 meters of water depth
 Long term OLM system
 Inverted K configuration

On-line Detection of Structural Failure

4-legged Platform with
permanent On-Line Structural
Integrity Monitoring system
onboard
F4 NS
B4 NS
F4 EW
B4 EW
North
F2 NS
B2 NS
F2 EW
B2 EW
Sudden Change in Natural Frequency
Results Data
0.4
NS1-F4NSA C.FREQUENCY
0.395
Sudden change in
NS frequency
Statistics (Hz)
0.39
0.385
0.38
0.375
0.37
F4 EW
F4 NS
0.365
B
4
B4ENS
W

North
0.36
Dec2006
0.4
Jan2007
Results
Data
Date
Feb2007
EW1-F4EW A C.FREQUENCY
0.395
F2 NS
B2 NS
Statistics (Hz)
0.39
0.385
0.38
0.37

B
2
E
W
Results Data
0.535
0.365
0.53
0.36
Dec2006
0.525
Statistics (Hz)
F2 EW
NO Change in EW
0.375
TOR1-F4NSA C.FREQUENCY
Jan2007
Date
0.52
Feb2007
Sudden change in
Torsional frequency
0.515
0.51
0.505
0.5
0.495
Dec2006
Jan2007
Date
Feb2007
Summary of Change
Natural
Frequency
Change
NS1
-2.8%
EW1
No Detectable
change
TOR1
-1.2%
Comparison of Measured With Model Analysis
Frequency
D NS1
(%)
D EW1
(%)
D TOR1
(%)
Observed
2.8
0.0
1.2
Possible brace severance with high probability
MD41
2.31
0.57
0.88
MH21
2.46
1.00
1.26
MH41
2.46
1.00
1.26
Possible brace severance but with less probability
MB41
1.48
0.19
0.53
MD21
1.76
0.22
0.50
Natural Frequencies After Repair
Hourly
Natural Frequency Values
24-hour Mean
0.38
NS1 (Hz)
Guide
0.37
28-day mean
LoLo
0.36
Absolute Low er Limit
03 04 05 06 07
08 09 10 11
12 13 14 15
16 17 18 19 20
21 22 23 24
25 26 27 28
29 30 01 02
03
Guide
EW1 (Hz)
0.39
0.38
Absolute Low er Limit
28-day mean
LoLo
0.37
03
04 05 06 07
08 09 10 11
12 13 14 15
16 17 18 19 20
21 22 23 24
25 26 27 28
TOR1 (Hz)
0.515
29 30 01 02
03
Guide
0.51
0.505
Absolute Low er Limit
0.5
28-day mean
LoLo
0.495
03 04 05 06 07
08 09 10 11
12 13 14 15
16 17 18 19 20
Date: Sep - Oct 2007
21 22 23 24
25 26 27 28
29 30 01 02
03
Major Benefits of Response Measurements

To reduce periodic sub-sea structural inspection.


Instant detection of subsea structural failure after seismic
event, storms, hurricanes, impact etc


Hence reduce the probability of catastrophic failure.
Assess the effectiveness of a repair to platform


Allow the operator to focus on damaged platforms.
Reduce the time the structure is at risk to a failed member.


Either by extending the time between regular inspection or by
omission after an event.
Show that the platform stiffness has returned to an acceptable
level
Tune Structural Model, for assessing effect of modifications
and damage to the structure.
Consideration
Consideration should be given to applying
this technology to the 40 or so shelf
installations that the deepwater production
relies on.
THE END
Thank you