Revised Outer Continental Shelf Lease Exploration Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

Appendix J 

Critical Operations and Curtailment Plan 

 
Revised Outer Continental Shelf Lease Exploration Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

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SHELL GULF OF MEXICO INC.

3601 C Street, Suite 1000 

Anchorage, AK 99503

CRITICAL OPERATIONS AND 

CURTAILMENT PLAN 

Chukchi Sea, Alaska 

May 2011

Submitted to: 

U. S. Department of the Interior 

Bureau of Ocean Energy Management, 

Regulation and Enforcement 

Alaska OCS Region 

Submitted by:

Shell Gulf of Mexico Inc. 

Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. i May 2011 

Table of Contents 

1. Introduction ..........................................................................................................................1

2. Planned Critical Operations .................................................................................................2

3. Unplanned Critical Operations ............................................................................................3

4. Other Potentially Critical Operations...................................................................................3

5. Circumstance/Conditions Requiring Curtailment ................................................................4

5.1 Severe Weather ........................................................................................................4

5.2 Sea Ice ......................................................................................................................4

5.3 Sea Spray .................................................................................................................4

5.4 Unavailability of Materials, Personnel, and / or Equipment ....................................5

5.5 Well Control.............................................................................................................5

6. Time Requirements ..............................................................................................................6

6.1 Secure Time (ST) .....................................................................................................6

6.2 Move-off Time (MT) ...............................................................................................6

6.3 Total Time (T-Time) ................................................................................................7

6.4 Hazard Time (HT)....................................................................................................7

7. Curtailment Decision Process ..............................................................................................7

7.1 Key Personnel ..........................................................................................................7

7.2 Curtailment Decision Protocol .................................................................................8

8. Organization and Reporting Chart .......................................................................................9

9. Training ..............................................................................................................................10

Reference Documents: 

• 30 CFR Part 250.417 (e) 

• Shell Gulf of Mexico Inc. Ice Management Plan (Chukchi Sea) 

 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. ii May 2011 

ACRONYMS & ABBREVIATIONS 

API American Petroleum Institute 

BOEMRE Bureau of Ocean Energy Management, Regulation and Enforcement 

BOP blowout preventer 

CFR Code of Federal Regulations 

COCP Critical Operations and Curtailment Plan 

Discoverer Motor Vessel Noble Discoverer 

DNV Det Norske Veritas 

ft feet (foot) 

HSSE Health, Safety, Security and Environment 

HT Hazard Time 

IMO International Maritime Organization 

IMP Ice Management Plan 

LMRP lower marine riser package 

m meter(s) 

MT Move-off Time 

M/V Motor Vessel 

Plan Critical Operations and Curtailment Plan 

RARs Rig Anchor Releases 

RS/FO Regional Supervisor, Field Operations 

Shell Shell Gulf of Mexico Inc. 

SIWAC Shell Ice and Weather Advisory Center 

ST Secure Time 

T-Time Total Time 

USCG U.S. Coast Guard 

VMT Vessel Management Team 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Offshore Inc. 1 May 2011 

1. Introduction 

The primary purpose of this Critical Operations and Curtailment Plan (COCP, or Plan) is to 

document precautionary measures to minimize the likelihood and consequence of an oil spill 

while drilling exploration wells in the Chukchi Sea and to protect personnel, equipment and the 

environment. The COCP is arranged to: 

• Identify critical operations 

• Identify circumstances that may cause curtailment 

• Identify relationships between the COCP and the Ice Management Plan (IMP) 

• Comply with all regulatory requirements. 

Drilling operations can be interrupted for a variety of reasons. Some factors affecting 

curtailment include: 

• Adverse ice movement, weather conditions, sea states and other environmental conditions 

that add risk to ongoing operations. 

• Time requirements for bringing support vessels to bear on a particular issue. 

• Loss of ice management vessel support due to mechanical issues or as a result of 

temporary reassignment of vessel(s) to another area (for example, to provide rescue, 

supply/logistics support, etc.). 

• Communications loss between vessels and/or between vessels and the shorebase(s). 

This plan identifies certain drilling activities designated as critical operations and discusses plans 

to delay, limit or cease these operations when hazards develop with the potential to harm 

personnel; damage vessels, equipment or the well; or result in a spill that could adversely impact 

the environment. This plan describes the decision-making process and identifies the lines of 

authority, responsibility and accountability for successfully handling critical operations. 

A companion plan to the COCP is the IMP, which details the process for making these critical 

decisions with regard to ice conditions. The IMP describes ice management operations, the flow 

of ice information, and how direction of the ice management vessels is accomplished. The “Ice 

Alert Procedures” contained within the IMP describe the ice alert levels, the decision process 

leading to their change, and the decision to return to the site. It also deals with well suspension 

operations, mooring system recovery, and well re-entry decisions associated with ice hazards in 

the Chukchi Sea. No critical operation will be started, or continued if already in progress, until 

the time required to perform the task is properly determined under the circumstances and that 

time is deemed to be sufficient for safe completion of the operation. 

Certain drilling operations are more likely than others to generate conditions that could lead to a 

well control incident or other incident that could result in harm to people, assets or the 

environment. This is particularly the case when subsurface formations capable of flowing 

formation fluids into the wellbore are exposed, or when the well has encountered abnormal 

pressures. 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 2 May 2011 

This COCP in conjunction with the IMP also satisfies 30 Code of Federal Regulations (CFR) 

Part 250.417 (e) as required for a “floating drilling unit contingency plan for moving off location 

in an emergency situation.” No contingency plan can adequately cover all conceivable situations 

and circumstances, nor is this plan intended to be a substitute for good judgment and experience 

in dealing with unexpected situations. 

Shell plans to use the drillship Motor Vessel (M/V) Noble Discoverer (Discoverer) to drill the 

proposed wells described in the revised Chukchi Sea Exploration Plan. The Discoverer is a true, 

self-contained anchored drillship. Station keeping is accomplished using the turret-moored, 

eight-point anchor system. The underwater fairleads prevent ice fouling of the anchor lines. 

Turret mooring allows orientation of vessel’s bow into the prevailing seas and/or ice drift 

direction to present minimum hull exposure to drifting ice. The vessel is rotated around the 

turret by hydraulic jacks. Rotation can be augmented by the use of the bow and stern tunnel 

thrusters. The hull has been strengthened for ice resistance by retrofitting sponsons to the ship’s 

hull. 

The Discoverer is classed by Det Norske Veritas (DNV) as a Mobile Offshore Drilling Unit for 

worldwide service. It is a “1A1 Ship-Shaped Drilling Unit l” and is capable of performing 

drilling operations offshore Alaska. The Discoverer has been issued with a DNV Appendix to 

Class stating: 

“the structural strength and material quality of the ‘Ice Belt’ formed by the 

sponsons below the 8950mm A/B level, have been reviewed against the 

requirements for the DNV ICE-05 Additional Class Notation and found to meet 

those requirements (as contained in DNV Rules for Classification of Ships, Pt 5 

Ch 1, July 2006) for a design temperature of -15 degrees C.” 

The Discoverer will comply with the requirements of 30 CFR Part 250.417, the IMO, the USCG 

and DNV. All drilling operations will be conducted under the provisions of 30 CFR Part 250 

Subpart D, API RP 53, 65 Part 2 and 75 and other applicable regulations and notices including 

those regarding the avoidance of potential drilling hazards, safety and pollution control. Such 

measures as inflow detection and well control, monitoring for lost circulation and seepage loss, 

and casing and cementing program designs will be the primary safety measures. Primary 

pollution prevention measures are the contaminated and non-contaminated drain systems, the 

mud drain system, and the oily water processing system. 

Structurally, the Discoverer is comparable to the Canmar drillships used safely and successfully 

in exploration campaigns in the Beaufort and Chukchi Seas into the 1990s. 

2. Planned Critical Operations 

Planned critical operations are those operations that are designed to occur during the exploration 

drilling program in the Chukchi Sea. Planned critical operations include, but are not limited to: 

• Drilling into a zone capable of flowing oil and/or gas 

• Conducting certain operations in a well where zones capable of flowing oil and/or gas are 

exposed or are anticipated of becoming exposed such as: 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 3 May 2011 

– Coring (whole or sidewall cores) 

– Pulling out of the hole with the drill string 

– Wireline logging in the open hole 

– Running casing, circulating and cementing 

– Continuing to drill after a well-related event (e.g., a kick) 

Not all of these planned critical operations will necessarily be conducted or encountered on each 

well during the exploration drilling program. Data collection and testing requirements will vary 

from well to well depending on previous results from offsets and the defined exploration 

objectives for the new well. 

3. Unplanned Critical Operations 

Certain operations are not planned in the normal course of drilling exploration wells, but they 

could be undertaken should situations arise in which they are required. If these unplanned 

operations are deemed to increase the risk of harm to people, assets or the environment they may 

be curtailed depending on the level of risk involved. Such operations could include: 

• Fishing for lost items in the well 

• Cutting and pulling casing/ milling casing window 

• Open hole sidetracking 

• Drilling into a lost circulation zone 

• Perforating 

• Remedial well work 

• Conducting well control operations (e.g., circulating a kick out of the hole) 

4. Other Potentially Critical Operations 

These are operations that could be considered critical depending on the well status and 

conditions at the time: 

• Moving back over a well after an emergency evacuation 

• Re-entering a suspended or temporarily abandoned (TAd)well 

• Anchor line tensioning 

• Accidental or unintentional riser disconnect 

• Oil or fuel spill 

• Heavy load lifting and handling during re-supply activities 

• Refueling 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 4 May 2011 

• Shipboard fire 

Should these conditions be encountered, severity and potential impact will be evaluated on a 

case-by-case basis and operations may be curtailed while dealing with them using safe methods 

and procedures. Again, good judgment is the key for dealing with such situations. 

5. Circumstance/Conditions Requiring Curtailment 

Several situations arise under which critical operations may be terminated, limited, or not 

commenced. These are listed and discussed briefly below: 

5.1 Severe Weather 

Wind and sea states can affect vessel motion (e.g., heel, pitch, roll, and heave) beyond safe 

operating limits and/or create conditions that make certain operations unsafe. Wind and currents 

can also result in ice movement that creates an unsafe condition for the vessel. 

Conditions for curtailment activities will depend on the performance of the drillship in the open 

water of the Chukchi Sea. The drillship behavior will be thoroughly analyzed upon mooring on 

the first drill site location, and it will be reevaluated as needed during drilling operations. 

Thresholds will be established for weather and sea conditions that will control: 

• Equipment preparation to curtail operations 

• Decision to cease drilling 

• Hanging off drillstring or otherwise suspending the well 

• Disconnecting riser 

• Moving the drilling vessel off the drill site 

The curtailment of critical operations as a result of severe weather is the responsibility of the 

Drilling Vessel Master with input provided by the Shell Drilling Foreman and the Noble Drilling 

Superintendent. 

5.2 Sea Ice 

Ice conditions that impact vessel station-keeping limitations (e.g., maximum horizontal 

displacement off well center) or endanger the vessel hull, will lead to curtailment of critical 

operations. Ice Alert Level details outlined in the IMP identify timelines as well as roles and 

responsibilities for action before the arrival of hazardous ice and are reviewed and evaluated 

daily in order to determine allowable operations. If there is insufficient time to complete a 

critical operation, or if a routine operation becomes critical before the arrival of the ice hazard, 

curtailment will be required. 

5.3 Sea Spray 

Freezing precipitation or sea spray on the vessel can quickly affect the Vertical Center of Gravity 

and possibly destabilize the drilling vessel. Wind exacerbates the situation by increasing ice 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 5 May 2011 

accumulations on the windward side of the drilling vessel. Such ice loading could lead to 

curtailment of critical operations. The prediction of ice loading under adverse conditions is 

required to determine whether certain operations can begin or continue before this hazard 

becomes acute. Information for developing ice loading predictions is provided through the 

consideration of actual on-site conditions in conjunction with forecasted weather advisory 

information from the Shell Ice and Weather Advisory Center (SIWAC) in Anchorage. The 

prediction of ice loading is the responsibility of the Drilling Vessel Master with input provided 

by the drilling vessel’s Ice Advisor.

5.4 Unavailability of Materials, Personnel, and / or Equipment 

Curtailment of critical operations may result from any of the following developments, or 

combinations thereof:

• Limited availability and/or capability of critical oil containment and cleanup equipment 

• Significant increase in oil spill control system response time 

• A lack of trained personnel or equipment for conducting a particular critical operation 

• Insufficient supply of drilling mud materials at the drill site for emergency well control 

purposes 

• Transportation for personnel, supplies and oil spill containment and cleanup equipment 

not readily available 

• Well control equipment, marine safety systems, fire detection, fire fighting or any other 

health, safety, security and environment (HSSE) critical systems that become inoperable 

or do not meet minimum standards 

• Loss of ice support vessel(s) 

• The absence of critical information and/or communications (e.g., ice data, weather 

forecasts, logistics) 

The curtailment of critical operations due to the unavailability of materials, personnel or 

equipment is the responsibility of the Shell Drilling Foreman. The decision to curtail activities 

as a result of diverting ice management resources away from the drilling vessel shall be made 

jointly by the Shell Drilling Foreman and the Drilling Vessel Master. The onshore Shell Drilling 

Superintendent (in consultation with the Noble Rig Manager) will endorse the plan or set 

priorities if agreement cannot be reached at the field level.

5.5 Well Control 

Critical operations, other than efforts to restore primary well control, will not be undertaken 

during a well control event (e.g., drilling will cease pending circulation of a kick out of the hole 

and adjusting mud density to prevent further kicks from entering the wellbore). The curtailment 

of critical operations due to a well control event is the responsibility of the Shell Drilling 

Foreman. 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 6 May 2011 

6. Time Requirements 

The IMP describes the color-coded alert levels associated with forecasting the arrival of a hazard 

(described below as Hazard Time [HT]). The IMP likewise describes how those time forecasts 

are used for deciding when to curtail or cease critical operations and it identifies various well 

securement methods as well as the applicable roles and responsibilities of key personnel 

involved. The definitions below describe the time elements used in the IMP alert level chart. 

6.1 Secure Time 

Secure Time (ST) is defined as the time in hours required for rig crews to cease critical 

operations and to secure and temporarily abandon the well in a way that prevents leakage of 

hydrocarbons, regardless of how long the well will be suspended. It also includes the time it 

requires to disconnect the Lower Marine Riser Package (LMRP) from the Blowout Preventer 

(BOP) and to secure the riser and LMRP on deck. 

ST varies and depends on the type of operation in progress at the time operations are suspended. 

For example, if the well is drilling in a zone capable of producing hydrocarbons, the time 

required to pull out of the hole with the drill string must be tempered by the maximum pipe 

speed to avoid swabbing a kick into the wellbore. It is also impacted by the method selected for 

suspending the well. If plugs are to be set, either mechanical or spotted cement slurries, ST will 

be greater than if, for example, a casing string has just been cemented and not drilled out. In the 

later case additional plugging may not be necessary and the drill string might simply be pulled to 

the surface or suspended in the wellhead and blind/shear rams subsequently closed. 

As noted earlier, various methods for suspending the well are outlined in the IMP. Detailed 

procedures for suspending the well will be available on the drillship while drilling. Regardless 

of which technique is selected, estimates of the time required to suspend the well are 

experienced-based and must be conservative to allow for unforeseen circumstances. The Shell 

Drilling Foreman, with input from the Shell Drilling Superintendent and the Shell Drilling 

Engineer will advise the Noble Rig Superintendent of the well suspension plan to be used. The 

Noble Drilling Superintendent is responsible for estimating the resulting ST and for conveying 

his determinations to the Drilling Vessel Master, the Shell Drilling Foreman and the rest of the 

Vessel Management Team (VMT). 

6.2 Move-off Time 

Move-off Time (MT) commences once the drilling riser and LMRP have been retrieved and 

secured, and it is defined as the time in hours required to safely store remaining items aboard the 

drilling vessel, recover moorings, and make the drilling vessel ready to evacuate the site. 

MT, like ST, varies considerably depending on a number of circumstances including sea state, 

weather conditions, the type hazard involved, and the method selected for mooring recovery. 

Horizontal displacement of the rig from the wellbore centerline may complicate release of the 

LMRP. Inadequate time available for recovering anchors using conventional means may require 

activation of Rig Anchor Releases (RARs) or allowing anchor wires to spool off winches. These 

methods are also identified in “Mooring System Recovery / Release”, Section VIII of the IMP. 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 7 May 2011 

The Drilling Vessel Master is responsible for estimating MT. Like the ST estimate, MT will be 

conservatively designed to allow for uncertainties. 

6.3 Total Time 

Total Time (T-Time) is the sum of ST and MT, and it is defined as the time required, in hours, to 

cease operations, secure the well and be ready to move off the drill site. 

6.4 Hazard Time 

Hazard Time (HT) is the time in hours remaining before the arrival of the hazard, regardless of 

type, at the drill site. The IMP outlines how the arrival of ice hazards in particular are predicted, 

based on observations of ice features by Ice Advisors and Specialists on support vessels and on 

the drilling vessel, combined with ice and weather predictions provided by the SIWAC. 

Other hazards (e.g. severe weather and sea spray) are predicted using a variety of sources 

including, but not limited to, the support vessel Ice Advisors and the SIWAC as well as the onsite routine observations of the Marine Mammal Observers who also report on environmental 

conditions as they regard sea state, weather and spray ice conditions aboard and in proximity to 

the drilling vessel. The potential for an earlier-than-forecasted arrival of a given hazard at the 

well site should be anticipated. Observation and reporting frequency from all sources must 

increase as HT decreases to ensure that appropriate measures are being employed to protect 

people, assets, and the environment. 

7. Curtailment Decision Process 

The decision process and the roles and responsibilities for dealing with ice hazards are addressed 

in the IMP. The decision processes and specific procedures for dealing with emergencies in 

general are in the drilling vessel operations manual kept on the drilling vessel for reference. In 

every case, the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) 

will be included in the process and will be kept informed of all operations, alerts, and decisions 

through verbal communications and written reports. 

7.1 Key Personnel 

The following on-site personnel have significant roles in determining when and how curtailment 

of critical operations will be undertaken: 

• Drilling Vessel Master 

• Shell Drilling Foreman 

• Noble Drilling Superintendent 

• Noble Chief Engineer 

• Ice Advisors 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 8 May 2011 

Together, the key personnel identified above make up the Vessel Management Team (VMT). 

This VMT ensures that all input from the various data sources are considered in making a 

decision to curtail operations. Determining critical operations and their curtailment in the face of 

approaching hazards rests primarily with the Shell Drilling Foreman with inputs from the rest of 

the VMT and the Shell Drilling Engineers, Shell Drilling Superintendent, and Well Delivery 

Manager. 

7.2 Curtailment Decision Protocol 

The curtailment decision protocol is described below, and covers steps to be taken from the time 

a hazard is recognized until ultimately, the drilling vessel is ready to depart location should the 

situation require. 

• Upon identifying that a hazard exists which may require curtailment, the Drilling Vessel 

Master will notify the Shell Drilling Foreman. The Shell Drilling Foreman, with the 

concurrence of the Shell Drilling Superintendent and Shell Drilling Engineer, will 

determine what operations will be curtailed based on hazard type, severity and projected 

arrival time. This decision will incorporate input from the VMT and will have the 

concurrence of the Drilling Vessel Master. 

• If the well needs to be suspended, a suspension procedure will be selected by the Shell 

Drilling Foreman and the Shell Drilling Engineer and approved by the Shell Drilling 

Superintendent. 

• The Shell Drilling Superintendent will submit the proposed suspension plan and ST 

details to the BOEMRE Regional Supervisor, Field Operations (RS/FO) for approval. 

• The Shell Drilling Foreman will advise the Noble Drilling Superintendent of the 

suspension procedure chosen, and the Noble Drilling Superintendent will estimate ST. 

The ST calculation will then be distributed to the Shell Drilling Foreman and the VMT as 

well as applicable shore support parties. 

• The move-off procedure and estimated time required will be determined by the Drilling 

Vessel Master. An estimate of Move-off Time (MT) will be provided to the Shell 

Drilling Foreman and the rest of the VMT as well as applicable shore support parties. 

• When the alert level described in the IMP reaches yellow status, well suspension 

procedures will be performed and the drilling vessel made ready to move off location as 

conditions require. The Drilling Vessel Master will ultimately make the decision to move 

the vessel to a safe location until the hazard has passed. 

• The decision to execute an emergency well suspension due to an unanticipated acute 

hazard (e.g., well control incident, shipboard fire) and the procedure selected to do so will 

be made by the Drilling Foreman (e.g., drop drill string, cut the drill pipe). Once the well 

is suspended, the Drilling Vessel Master will make the drilling vessel ready to move if 

necessary. The Well Delivery Manager, the Shell Drilling Superintendent and the 

BOEMRE RS/FO will be notified as soon as practicable after the drilling vessel has been 

made safe. 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 9 May 2011 

• The Shell Drilling Superintendent with the concurrence of the Shell Drilling Foreman and 

the Drilling Vessel Master will make the decision to move back onto the well and resume 

operations when it is safe to do so.

8. Organization and Reporting Chart 

Notification of the decision for curtailments to Shell, USCG and BOEMRE agency 

representatives will be made as soon as practical, but in a manner that does not interfere with the 

safety of the crew, environment, or vessel. All operations curtailment decisions will be 

documented on the Shell Daily Operations Report and conveyed to the on-site BOEMRE 

representative as they develop. Operations curtailment decisions will also be formally conveyed 

to BOEMRE on a weekly basis via the Well Activity Report and at the end of the well operations 

as part of the End of Operations Report. The following chart illustrates the lines of 

communication in the field and from the field to the shorebase. 

USCG Shell Drilling 

Superintendent 

BOEMRE 

Shell Ice and 

Weather 

Advisory Service 

Noble Rig Manager BOEMRE 

Representative 

Drilling Vessel 

Master 

Noble Rig 

Superintendent Shell Drilling 

Engineers 

Drilling Vessel 

Ice Advisor 

Noble Chief 

Engineer Shell Drilling 

Foreman 

Fennica 

(or similar) 

Tor Viking 

(or similar) 

Support Vessels 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 10 May 2011 

9. Training 

All personnel will be made aware of their roles and responsibilities described within this COCP 

and the IMP through a training program to be taught before the vessel is on site. All persons 

with a key position in the COCP will be provided a copy of this document, and training will be 

provided by Shell prior to deployment. This training will include a table-top exercise that will be 

carried out prior to initiating operations in the Chukchi Sea. 

Anticipated participants will be: 

• Shell and drilling vessel leadership (both Drilling and Marine Operations staff) 

• Oil Spill Response representative 

• Ice Information Center representatives 

• BOEMRE 

• Ice Advisors, Ice Observers and Ice Pilots 

• Anchor Handlers 

If necessary, this document will be updated and reissued, incorporating the lessons learned from 

the table-top exercise. 

Reference Documents: 

• CFR 30 Part 250.417(e) 

• Shell Gulf of Mexico Inc. IMP (Chukchi Sea)