Zero Visibility Operations Planning - DrillSafe

Petrel-7 Zero Visibility Operations Planning
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Chris Wilson
September 2011

Glossary of Terms
• TGB – Temporary Guide Base
• PGB – Permanent Guide Base
• ROV – Remotely Operated Vehicle
• Compatt – Acoustic Survey Beacon
• Bucket – Item that holds a Compatt
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What Causes Zero Visibility at Petrel
• Active Sedimentary Basin – ongoing sediment deposition
• Strong Currents
- Surface Currents
- Mid water currents Various directions and magnitudes
- Seafloor currents
• Soft seabed
• As a result of the above - offset wells have had to wait on
currents or current induced visibility
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Petrel Field Location
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Seabed Survey
Water Depth ~98m LAT
Petrel 7
Water Depth ~94m LAT
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Petrel 7 Shallow Seismic
Main Line
Petrel 7
Location
8m
200m
Ancient River Channel
In-filled with recent
sediments
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NW Field Seismic
Main Line
Multiple Ancient River
Channels In-filled
with recent sediments
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Impact of Environment on Operations
• Running TGB
- May end-up away from rig centre – due to strong currents
- May be landed on an angle if seabed soft or uneven
- Could sink in the soft seabed
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Impact of Environment on Operations
• Running 30” & 20” with PGB
- Could be pushed away from well centre
- PBG angle might be unknown if bulls eyes aren’t visible with ROV
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Impact of Environment on Operations
• Running the BOP
- With zero visibility – difficult to determine if rig is over well
centre
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Impact of Environment on Operations
• Shallow Gas Monitoring
- Unable to detect gas bubbles with ROV
Uh Oh!
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Impact of Environment on Operations
• ROV Damage
- Greater risk of ROV collision and entanglement
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Solution Criteria
• To overcome the potential problems associated with
Strong Currents and Zero Visibility a solution had to meet
the following criteria;
1. Determine Relative location of equipment on seabed
(not absolute location)
2. Wireless inclination measurements on TGB and PGB
3. “Pictures” in a zero visibility environment
4. ROV Friendly
5. Easily Deployable
6. Cost Effective (Stena Clyde spread rate on Petrel-7
~$25,000/hour)
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The “Vision”
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Recommended Solution - Positioning
• Long Base Line (LBL) array on the seabed
- Provide acoustic “relative” positioning of
subsea components (TGB, PGB, Casing etc.)
• Acoustic Inclinometers
- Provide real time wireless inclination of TGB
and PGB
- Even if the ROV can’t see the bullseyes the
inclination would be known
• LBL beacons on the TGB, PGB and Casing
- LBL beacons can “talk” to the LBL array
triangulating their relative positions
- LBL beacons house the Acoustic
Inclinometers
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Recommended Solution – Visibility (ROV)
• Ultra Short Base Line (USBL) positioning beacon on the ROV
- ROV’s position can be tracked real time – even if the ROV becomes
disoriented or gets lost with zero visibility
- USBL beacon on ROV used to position LBL array on the seafloor
• Multi-beam Sonar on the ROV
- A multi-beam sonar provides a 3D sonar image even in zero visibility
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USBL vs LBL
• Ultra-short Baseline (USBL)
systems calculate the position of
a subsea target by measuring
the range and bearing from a
vessel mounted transceiver to an
acoustic transponder fitted on
the target e.g. ROV.
• With Long Baseline (LBL)
systems. The baseline is on the
seabed instead of the transceiver
hence the name ‘Long Baseline’.
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2D Sonar vs Multi-Beam Sonar
2D Sonar
Multi-Beam Sonar
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Operational Challenges
• Deploying LBL array
- Soft Seabed
- ROV friendly Bucket Structures
- Accurate Positioning
• Acoustic Inclinometer Installation
- Modify TGB and PGB to house Inclinometer
- Perform full Dimensional Check
- ROV Friendly
• ROV Modifications
- Multi-beam Sonar installation and checks
- Installation of a positioning beacon
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Acoustic Inclinometer Calibration
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Installation of the LBL Array
• Beacons lowered to seafloor through moonpool on a tugger
• ROV complete with USBL beacon deployed each beacon
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Array location on the Seabed
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Multi-Beam Sonar
• Initial results not encouraging
• Visibility better than anticipated – main focus was on LBL
system
• Field testing and fault finding difficult due to critical path
operations
• Post operational analysis indicated an earth fault between the
sonar and the ROV which lead to spurious images
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Mobile Transponder on 20” Casing
• 1 x Mobile Transponder compatt installed on the 20” casing
shoe – inverted to allow easy removal with the ROV.
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Actual Results – Running Casing
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Acoustic Inclinometer Performance
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Acoustic Inclinometers
• Inclinometers moved within the buckets – either caused by
currents or drilling induced vibration
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Outcomes & Lessons
• LBL Array was easy to deploy
• Rig based USBL beacon not designed to work on ROV –
positioning of LBL beacons not accurate
• Absolute Calibration of the LBL array from a MODU is difficult,
however this was only required this time due to USBL beacon
on ROV not functioning as intended
• Multi-beam sonar did not work as expected (earth fault)
• Inclinometers were effected by currents &/or Drilling Vibration
– giving erroneous readings initially
• Tracking of casing location worked well
• LBL Technology was proven as viable for this application
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Lessons
• Allow time to field trial multi-beam sonar
• Ensure acoustic inclinometers need to have a snug fit in the
buckets
• ROV positioning beacon to be a field proven dedicated USBL
system – don’t rely on the rigs BOP beacon
• Beacon on the shoe of the 30” casing would not allow casing
to fit through PGB.
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Questions
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