part of section 15

Prakash Bahadur Thapa Memorial University, St. John’s, NL, Canada, A1B 3X5 Corresponding author: Email: [email protected]; Tel: +1(709) 330-8666

Abstract In this tandem offloading simulation and Risk Bow tie Approach analysis I am taking the three offloading systems evaluated, a base case has been determined with SPM CALM buoy as a primary offloading system and a tandem offloading as a back-up/contingency system. The objective of this tandem offloading study is to simulate the tandem offloading operations under representative met ocean conditions identified from the preliminary operability assessment for the tandem offloading system. Eight representative met ocean cases were selected from the site specific conditions. The vessel particulars and hydrodynamic characteristics were scaled from the established database in SHUTTLE. Time domain simulations were made for tandem offloading operations using MARIN software SHUTTLE. This numerical simulation study on the contingent tandem offloading system to suggest that it is feasible to transfer the cargo under selected representative met ocean cases with up to 3 tugs (1x100 tones BP and 2x60 ton BP). 

In no cases considered for this study, the maximum hawser load exceeded 150 ton or 1,471 kN. The specified operating limit on cyclic hawser load, a maximum 100 ton or 981 kN load occurring no more than 5 times/hour, could be achievable by appropriately deploying the tugs.



In most selected cases, 2 tugs (1x 100 ton BP and 1x 60 ton BP) are required to maintain the off take tanker heading and position. These included the cases under the cross wind and current conditions, and cases under beam on wind and current in parallel.



In case of strong wind (15 m/s) from the beam with cross current stern on, three tugs (1x100 ton BP and 2x60 ton BP) were needed to meet the operating criteria.

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When metocean conditions are collinear with stern on wind and current, 1x100 ton BP astern pulling tug was required to control the heading and position of the off take tanker.



Only 1x60 ton BP tug or 1x100 ton tug with reduced BP) was needed when all environmental elements action on bow with quartering wind and current on either side of the FPSO .



The SHUTTLE analysis for more metocean conditions stretched beyond the environmental limits, different loading conditions of the FPSO and the off take tankers updating the predefined limiting metocean conditions.



Study on hawser configuration (composition and length) and installation of constant tension winches with an aim to reduce cyclic peak load of the hawser design through numerical simulation.



Assessment of the tug performance in field conditions and installation of constant tension winches better understanding of the tugs’ capability of controlling the off take tanker heading and position through numerical simulation and bridge simulation/physical model test.



Implementation of monitoring, inspection and maintenance programs during operations (Operation).

1.0 INTRODUCTION From the three alternative offloading systems evaluated, a base case has been determined with SPM CALM buoy recommended as a primary offloading system and a tandem offloading as a backup/contingency system. It is expected that the operability of the SPM system is over 95% uptime. The tandem offloading system, however, offers much lower uptime below 60% (mainly due to the strong currents). The operability assessment for tandem offloading was performed by applying predefined operating criteria to time traces of met ocean conditions. Generally the reliability of the offloading operability could be improved by time-domain simulation of the recurring offloading operations over representative met ocean time traces. The objectives of this tandem offloading study are: 

Simulate the tandem offloading operations under representative metocean conditions identified from the preliminary operability assessment for the tandem offloading system,



Verify if the limiting metocean conditions identified are acceptable in terms of hawser loads, tanker excursions and tug operations,



Confirm the feasibility of the tandem offloading as a backup/contingency offloading system



Conduct an

initial assessment of the system behaviour under selected representative

environmental conditions 

Provide operational guidance to improve the safety of the tandem offloading system.

2.0 Study Basis Data 2.1 Operating Criteria for Tandem Offloading Tandem Offloading Criteria are: Distance Floating production Storage and Offloading (FPSO) tanker: >= 40 m Hawser load:

981 kN /hr 0

Min Heading (deg) 205.01

Max Heading (deg) 205.16

Min Heading (deg) 197.99

Max Heading (deg) 198.64

Within ±60 deg sector Yes

Table 4.6 Results of case 3 with 1x60 tones tug assistance 5.0 Conclusions and recommendations

5.1 General This numerical simulation study on the contingent tandem offloading system suggested that it is feasible to transfer the cargo under selected representative metocean cases with up to 3 tugs (1x100 ton BP and 2x60 ton BP). 5.2 Tug Requirement In most selected cases, 2 tugs (1x 100 ton BP and 1x69 ton BP) are required to maintain the off take tanker heading and position. These included the cases 6 ~ 8 under the cross wind and current conditions, and cases 1 ~ 2 under beam on wind and current in parallel. In case of strong wind (15 m/s) from the beam with cross current stern on (case 5), three tugs were needed to meet the operating criteria.

When metocean conditions are collinear with stern on wind and current (case 4), 1x100 tons BP astern pulling tugs was required to control the heading of position of the offtake tanker. Case 3 represents the metocean condition when all environmental elements action on bow with quartering wind and current on either side of the FPSO. In this case, only 1x60T BP tug was required. 5.3 Hawser Load In no cases selected for this study, the maximum hawser load exceeded 150 ton or 1,471 kN. The specified operating limit on cyclic hawser load could be achieved by appropriately deploying the tugs. It should be noted that an increase of the BP of the astern pulling tug could help reduce the heading difference of two vessels, but also increase the occurrence of excessive cyclic hawser load. Alternatively, it is worthwhile to explore the different composition and length of the hawser to reduce the cyclic load and thereby optimize the tug BP requirement. 5.4 Recommendations The following recommendations for this study on the tandem offloading for FPSO: 

Metocean conditions stretched beyond the environmental limits, different loading conditions of the FPSO and the off take tankers – updating the pre-defined limiting metocean conditions.



This study on alternative hawser configuration (composition and length) and installation of constant tension winches with an aim to reduce cyclic peak load of the hawser – design through numerical simulation and physical model test.



Assessment of the tug performance in field conditions and installation of constant tension winches – better understanding of the tugs’ capability of controlling the off take tanker heading and position through numerical simulation and bridge simulation/physical model test.



Monitoring the hawser load, the tanker heading position during any offloading operation to providing better communication to and feedback control of the assisting tugs (Operation), regular inspection and maintenance of the hawser and other mooring equipment. (Operation).

6.0 Bow tie Risk assessment Approach

6.0 Bow Tie Analysis Hazards, Threats and Barriers

Figure 6.1 off take Tanker Approach

HAZARDS

THREATS

BARRIERS AND CONTROLS

Offtake Tanker

Ocean Current Conditions

Berthing Procedure

Wind and Sea Conditions Berthing Procedure

INPUT Current Monitoring Equipment (Redundancy of monitoring equipment requested in MOC 75) INPUT Berthing Tugs Specifications (Set at 120 ton bollard Pull for purpose of review)

Ocean Current operations limit set in Berthing Procedure INPUT (Wave info received from wave buoy) Wind and Wave Monitoring Equipment fitted to FPSO requested in MOC 75

Pilot Training and Competence

Wind and Wave operations limit set in Berthing Procedure

Tanker Loss of Power

Berthing Tugs 2 x 100 %

Pilot Training and Competence Berthing Tugs 2 x 100 %

Offtake Tanker Vetting Process Tanker uncontrolled powered approach

TOP EVENT Berthing Procedures

Loss of Communications with tanker

Lack of training/experience of Pilot or Berthing Tug Crews

Squalls

Duplication of Radio Equipment on tanker and FPSO (Vessel Vetting Process)

Pilot and Tug Crew Selection Process

Secure power Supplies on tanker and FPSO Vessel Vetting process)

Training plans and Competence Assurance System

Pilot Training and Competence

Berthing Procedures

Berthing Tugs 2 x 100 %

Dedicated radio Channels

Tandem Offloading Simulator Training

Weather Radar Surveillance on Tanker, Berthing Tugs, and FPSO Berthing Procedures (Squalls)

Collision between FPSO and Offtake Tanker on approach under pilotage

Figure 6.2 off take Tanker Approach (Continued)

HAZARDS

Offtake Tanker


THREATS

Agreed manning level for operation (Service Level Agreement required for back up Pilot)

Shortage or incapacity of Pilot

Fitness and health checks and monitoring of Pilots’ health

Human Error leading to inappropriate tanker approach

Berthing Procedures (Duties of Pilots FPSO/Tanker Navigation Instrumentation Competence of Pilots Berthing Tugs 2x100%

MOC Differential GPS on FPSO linked to portable DGPS on Offtake Tanker

Towline and/or fixing failures on tug or Off take tanker

Distraction caused by FPSO (ESD, blow-down to flare or other FPSO operation, process upset or emergency situation

TOP EVENT Collision between FPSO and Offtake Tanker on approach under pilotage

Towline Specifications Tug and tanker vetting process (vessels and crews

Towline and fixing inspection and maintenance

FPSO Operating procedures for Simultaneous Operations and Tandem Loading Operations

Berthing Procedures Tug connection and towing

Berthing Tugs 2x100%

Berthing Procedure Emergency Response

Figure 6.3 off take Tanker Approach Continued Recovery Measures

CONSEQUENCES

Emergency Procedures for Tanker Collision

Structural Damage to FPSO Hull

ESCALATION

Vessels Continues to cause damage after impact (possible damage to risers

Note Riser Protection not designed to withstand energy levels of drifting Offtake Tanker

FPSO Mooring Design FPSO Hull Design

FPSO Double Hull Construction No outboard hydrocarbon tanks

TOP EVENT Collision between FPSO and Offtake taker on approach under pilotage

Emergency Response Procedures (Pollution Incident Control)

Emergency Response Training (Pollution incident Control) Self-Sealing Hose Breakaway Coupling

Fire Fighting Capabilities of FPSO and Tugs

FPSO ESD and Emergency procedures

Tug Assistance and Vessels Engines

Remote Loading ESD controlled by FPSO and Tanker

Emergency Disconnect System and Procedures

Fire

Pollution


Tug Assistance and Vessels Engines Note Riser Protection not designed to withstand energy levels of drifting Offtake Tanker

Escalated explosion due to hydrocarbon leakage from Offtake Tanker

No Explosion Protection on Aft of FPSO to mitigate an escalated event from Offtake Tanker

Figure 6.4 off take tanker Approach Continued Recovery Measures

CONSEQUENCES

Emergency Response procedure

Operating procedure limiting access to aft deck of FPSO during berthing

Loss of life

Personal Injury

SIMOPS Procedure Work in Machinery space during berthing

Loss of Reputation Local

TOP EVENT

ESCALATION

SNEPCO PR Contingency plan

Collision between FPSO and Offtake taken on approach under pilotage

Repair plans and “insurance” spares and equipment

Loss of production

Escalated damage/pollution/loss of asset due to collision

SHELL Group PR Contingency Plan

International Loss of Reputation

Figure 6.5 off take Tanker Moored


THREATS Note Normal Tanker manning not considered adequate for Bonga Tandem loading Operations

HAZARDS

Offtake Tanker Moored to FPSO

Adequate manning of tugs and Offtake Tanker

Tanker and Tug Crew Fatigue during Loading

Mooring Hawser Failure

Hawser

Mooring Tugs 2x 100%

Mooring hawser Specifications

Crew Working Hour Limitations

Adequate Manning for pilot/Loading master

Hawser maintenance and Inspection

Hawser load monitor via Hawser load Monitoring Instrumentation

MOC 75 Differential GPS on FPSO linked to portable DGPS on Offtake Tanker

Accidental Release Release system for hawsers fails in closed position

Loading Procedure

Collision between FPSO and Offtake Tanker whilst moored to FPSO

Mooring Tugs 2x 100%

Human Error FPSO/Tanker Navigation Instrumentation


Competence of Pilots

Berthing Tugs 2x100%

TOP EVENT

Adequate Manning for pilot/Loading master

Figure 6.6 off take Tanker Moored (Continued)

Recovery Measures

CONSEQUENCES



ESCALATION




TOP EVENT Collision between FPSO and Offtake taker whilst moored to FPSO


Emergency Response Training (Pollution incident Control) Self-Sealing Hose Breakaway Coupling



Pollution



Note Riser Protection not designed to withstand energy levels of drifting Offtake Tanker

Remote Loading ESD controlled by FPSO and Tanker

Emergency Disconnect System and Procedures

Fire

Tug Assistance and Vessels Engines



Figure 6.7 off take Tanker Moored

Recovery Measures

CONSEQUENCES

Emergency Response procedure

Operating procedure limiting access to aft deck of FPSO during berthing

Loss of life

Personal Injury

SIMOPS Procedure Work in Machinery space during berthing

Loss of Reputation Local

TOP EVENT

ESCALATION

SNEPCO PR Contingency plan

Collision between FPSO and Offtake taker whilst moored to FPSO

Repair plans and “insurance” spares and equipment

Loss of production

Escalated damage/pollution/loss of asset due to collision

SHELL Group PR Contingency Plan

International Loss of Reputation

Figure 6.8 off take Tanker Departing


THREATS

HAZARDS

Offtake Tanker Moored to FPSO

Emergency Disconnect system on FPSO will release Hawser (Can operate even with mooring hawser under tension

Disconnect not possible due to system failure

Tanker

Manoeuvres towardsFPSO in order to Disconnect Mooring Hawser


Emergency Disconnection procedures

FPSO/Tanker Navigation Instrumentation Competence of Pilots Tanker Departure Procedures

TOP EVENT Berthing Tugs 2x100%

Collision between FPSO and Offtake during departure

Figure 8.9 off take Tanker Departing (Continued) Recovery Measures

CONSEQUENCES



ESCALATION




TOP EVENT Collision between FPSO and Offtake tanker during departure



Pollution



Emergency Response Training (Pollution incident Control)



Fire



Figure 6.10 Mooring Hawser Failures

HAZARDS

Mooring Hawser Tension

THREATS

Excessive Loading


Hawser Design Hawser Load Monitoring

Mooring System Operating Procedures

Cyclic Loading Hawser Design

Hawser Replacement Schedules

Crew Training Mooring System Operating Procedures

Degradation

Mechanical Damage

Hawser Maintenance and Inspection

Mooring System Design

Hawser Maintenance and Inspection

Crew Training

TOP EVENT Crude Export Tandem Mooring Failure Manufacturing Defects

Quality Assurance Process

Factory Acceptance Test

Figure 6.11 Mooring Hawser Failures

Recovery Measures

CONSEQUENCES

ESCALATION

Tanker Breakout

TOP EVENT Crude Export Tandem Mooring Failure

Berthing Tugs 2 x 100%

Emergency Procedures

Emergency Procedures Training and Drills

Hose Breakout

See Sheet for Loading Hose Failure Loading Hose Failure (See Loading Hose Failure Sheet)

Collision between Offtake Tanker and FPSO

See Sheeting for Collision During whilst Moored

Figure 6.12 Loading Hose Failure

HAZARDS

Crude Oil Hydrocarbons

THREATS

Mechanical Damage


Hose Design and QA

Hose Inspection and Maintenance Procedures

Hose Pressure Testing Prior to Use

Hose Design

Loading Pump Press Controlled and HP Shut down system (System Designed to API 14C)

Overpressure

Shock Loads as a result of Pressure Surges

Hose Design

Loading Pump Press Controlled and HP Shut down system (System Designed to API 14C) Hose Selfsealing

Excessive Tension

TOP EVENT Manufacturing Defects

Autosubmergence Environmental and Actinic Degradation Seawater and Fatigue Damage

Hose Design

Manufacturer Selection OCIMF

Inspection and Maintenance Procedures

Loading Hose Failure during Loading Operations

Marine Breakaway Coupling

Factory Acceptance Testing Quality Assurance Process

Hose Design Pressure Test

Sabotage

Security Procedures

Inspection and Maintenance

Damage caused by Supply Boats Supply Boat Operating Procedures

Hose Design (Abrasion Resistance)

Pressure Test before Use

Figure 6.13 Loading Hose Failure ESCALATION CONSEQUENCES

Recovery Measures

Pollution

TOP EVENT Crude Export Loading Hose Failure during Loading Operations

Quantity Oil pumped/Quantity Received Reconciliation

Visual Alert form watchman on FPSO/Tug or Offtake Tanker

Emergency Shutdown on Offtake Tanker or FPSO

Emergency Shutdown on Offtake Tanker or FPSO

Loss of Product

Loss of Reputation

Collision between Offtake Tanker and FPSO