CRITICAL OPERATIONS AND 

CURTAILMENT PLAN 

Chukchi Sea, Alaska 

March 2015

Submitted to:

U. S. Department of the Interior

Bureau of Ocean Energy Management 

Alaska OCS Region

Submitted by:

Shell Gulf of Mexico Inc.

Shell Gulf of Mexico Inc.

3601 C Street, Suite 1000

Anchorage, AK 99503
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. i March 2015

Table of Contents

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

2. Planned Critical Operations.................................................................................................3

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

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

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

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

5.2 Sea Ice......................................................................................................................5

5.3 Sea Spray .................................................................................................................5

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

5.5 Well Control.............................................................................................................6

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

6.1 Secure Time .............................................................................................................6

6.2 Move-off Time.........................................................................................................7

6.3 Total Time................................................................................................................7

6.4 Hazard Time.............................................................................................................7

7. Curtailment Decision Process..............................................................................................8

7.1 Key Personnel ..........................................................................................................8

7.2 Curtailment Decision Protocol.................................................................................9

8. Organization and Reporting Chart.....................................................................................10

9. Training..............................................................................................................................11

Reference Documents:

 30 CFR Part 250.417 (e)

 Shell Gulf of Mexico Inc. Drilling Ice Management Plan, Chukchi Sea, Alaska
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. ii March 2015

ACRONYMS & ABBREVIATIONS

API American Petroleum Institute

BOEM Bureau of Ocean Energy Management 

BOP Blowout Preventer

CFR Code of Federal Regulations

COCP Critical Operations and Curtailment Plan

DIMP Drilling Ice Management Plan

Discoverer M/V Noble Discoverer

DNV Det Norske Veritas

ft. feet (foot)

HSSE Health, Safety, Security and Environment

HT Hazard Time

IMO International Maritime Organization

LMRP Lower Marine Riser Package

m meter(s)

MT Move-off Time

M/V Motor Vessel

OIM Offshore Installation Manager

Plan Critical Operations and Curtailment Plan

Polar Pioneer Mobile Offshore Drilling Unit (MODU) Transocean Polar Pioneer

PSO Protected Species Observer

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

TA Temporarily Abandoned

T-Time Total Time

USCG U.S. Coast Guard

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

Shell Gulf of Mexico Inc. 1 March 2015

1. Introduction

The primary purpose of this Critical Operations and Curtailment Plan (COCP) 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 Drilling Ice Management Plan (DIMP)

 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 DIMP, which details the process for making these critical 

decisions with regard to ice conditions. The DIMP 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 DIMP 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 required time 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 March 2015

This COCP in conjunction with the DIMP 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) and the 

Mobile Offshore Drilling Unit (MODU) Transocean Polar Pioneer (Polar Pioneer) 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 metocean conditions 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. Ice 

strengthened sponsons have been retrofitted to the ship’s hull. The Discoverer is classed by Det 

Norske Veritas (DNV) as a MODU 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 Polar Pioneer is classes by DNV as MODU for worldwide service. It is a non-selfpropelled, “SPM thruster assisted” semisubmersible offshore drilling unit of twin-hull 

configuration. The rig is a “+A1 Column Stabilized Unit” and is capable of performing drilling 

operations offshore Alaska.

Positioning is accomplished with a combination of an eight-point all chain catenary mooring 

system and dynamic positioning system.

The Polar Pioneer was built in 1985, with unlimited operation area, in accordance with the 

“Norwegian Maritime Directorate” and to “Det Norske Veritas regulations” current at that time. 

While operating in Norwegian waters, the installation, with its inventory, equipment, crew and 

machinery is required to comply with current rules and regulations for operation on the 

Continental Shelf of Norway.

The Discoverer and the Polar Pioneer will comply with the requirements of 30 CFR Part 

250.417, the IMO, the USCG and DNV. All exploration 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.
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 3 March 2015

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:

– 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) 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 4 March 2015

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 (TA) well

 Anchor line tensioning

 Accidental or unintentional riser disconnect

 Oil or fuel spill

 Heavy load lifting and handling during re-supply activities

 Refueling

 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., 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 drilling unit in the 

open water of the Chukchi Sea. The drilling unit behavior will be thoroughly analyzed upon 

mooring on the first drill site location, and it will be re-evaluated 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 drill string or otherwise suspending the well

 Disconnecting riser

 Moving the drilling unit off the drill site
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 5 March 2015

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 DIMP 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 unit. Wind exacerbates the situation by increasing ice 

accumulations on the windward side of the drilling unit. 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 Unit Master/OIM with input 

provided by the drilling units 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, firefighting or any other 

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

or do not meet minimum standards

 Loss of ice management 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 Supervisor. The decision to curtail activities 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 6 March 2015

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

jointly by the Shell Drilling Supervisor and the Drilling Unit Master/OIM. The onshore Shell 

Wells Operations Team Leader (in consultation with the drilling contractor’s Rig Manager) will 

endorse the plan or set priorities if agreement cannot be reached at the field level. The plan will 

be communicated with the Arctic venture to ensure SIMOPS involvement as required.

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 

Supervisor.

6. Time Requirements

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

hazard (described below as Hazard Time [HT]). The DIMP 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 DIMP 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 considered 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 

latter 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 DIMP. 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 experiencedbased and must be conservative to allow for unforeseen circumstances. The Shell Drilling 

Supervisor, with input from the Shell Wells Operations Team Leader and the Shell Wells 

Engineer will advise the drilling contractor’s Rig Superintendent of the well suspension plan to 

be used. The drilling contractor’s Drilling Superintendent is responsible for estimating the 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 7 March 2015

resulting ST and for conveying his determinations to the Drilling Unit Master/OIM, the Shell 

Drilling Supervisor and the rest of the Unit Management Team (VMT).

6.2 Move-off Time 

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

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

drilling unit, recover moorings, and prepare the drilling unit to evacuate the site.

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

weather conditions, the type of 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 DIMP.

The Drilling Unit Master/OIM 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 DIMP 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 unit, 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, Ice Advisors and the SIWAC as well as the on-site routine 

observations of the Protected Species Observers (PSO) who also report on environmental 

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

the drilling unit. 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.
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 8 March 2015

7. Curtailment Decision Process

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

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

general are in the drilling unit operations manual kept on the drilling unit or reference. In every 

case, the Bureau of Safety and Environmental Enforcement (BSEE) 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 Unit Master/(OIM)

 Shell Drilling Supervisor

 Rig contractor’s Drilling Superintendent

 Rig Chief Engineer/Barge Captain

 Ice Advisors

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

The decision to curtail critical well operations in the face of approaching hazards rests with the 

Shell Drilling Supervisor with inputs from the VMT, Shell Wells Engineers, Shell Wells 

Operations Team Leader and the Shell Well Operations Manager. The Shell Drilling Supervisor 

will be aided in this decision by the Master/OIM of the drilling unit.

The decision to depart the well site for safety reasons rests with the Master/OIM who will be 

informed by the VMT in regards to well status and threats of severe weather or Hazardous 

Ice. Nothing in this document takes away the authority and accountability of the Master/OIM. 
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 9 March 2015

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 unit is ready to depart location should the 

situation require.

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

Senior Drilling Supervisor and the Shell Wells Engineer and approved by the Shell Wells 

Operations Team Leader. 

 Upon identifying that a hazard exists which may require curtailment, the Drilling Unit 

Master will notify the Shell Drilling Supervisor. The Shell Senior Drilling Supervisor, 

with the concurrence of the Shell Wells Operations Team Leader and Shell Wells 

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 Unit Master/OIM.

 The Shell Senior Drilling Supervisor will advise the rig contactor’s Drilling 

Superintendent of the suspension procedure chosen, and the rig contractor’s Drilling 

Superintendent will estimate ST. The ST calculation will then be distributed to the Shell 

Senior Drilling Supervisor and the VMT as well as applicable shore support parties.

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

Unit Master/OIM. An estimate of MT will be provided to the Shell Senior Drilling 

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

 The Shell Wells Operations Team Leader will submit the proposed suspension plan and

ST details to the BSEE Regional Supervisor, Field Operations (RS/FO) for approval

 When the alert level described in the DIMP reaches yellow status, well suspension 

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

conditions require. The Drilling Unit Master/OIM will ultimately make the decision to 

move the unit 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 Shell Senior Drilling Supervisor (e.g., drop drill string, cut the drill pipe). 

Once the well is suspended, the Drilling Unit Master/OIM will make the drilling unit 

ready to move if necessary. The Shell Well Operations Manager, the Shell Wells 

Operations Team Leader and the BSEE RS/FO will be notified as soon as practicable 

after the drilling unit has been made safe. 

 The Shell Wells Operations Team Leader with the concurrence of the Shell Senior 

Drilling Supervisor and the Drilling Unit Master/OIM will make the decision to move 

back onto the well and resume operations when it is safe to do so.
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 10 March 2015

8. Organization and Reporting Chart

Notification of the decision for curtailments to Shell, USCG and BSEE 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 unit. All operations curtailment decisions will be documented on the Shell 

Daily Operations Report and conveyed to the on-site BSEE representative as they develop. 

Operations curtailment decisions will also be formally conveyed to BSEE 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 Wells 

Operations Team 

Leader

BSEE

Shell Ice and 

Weather 

Advisory Service

Rig contractor’s Rig 

Manager BSEE 

Representative

Drilling Unit 

Master / Offshore 

Installation 

Manager

Rig contractor’s Rig 

Superintendent Shell Wells 

Engineers

Drilling l Unit

Ice Advisor

Rig Chief Engineer 

/ Barge Captain

Shell Drilling 

Supervisor

Fennica

(or similar)

Tor Viking

(or similar)

Support Vessels
Critical Operations and Curtailment Plan Chukchi Sea, Alaska

Shell Gulf of Mexico Inc. 11 March 2015

9. Training

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

and the DIMP through a training program to be taught before the drilling unit 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 unit leadership (Drilling, Logistics and Marine Operations staff)

 Oil Spill Response representative

 Ice Information Center representatives

 BSEE

 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. DIMP (Chukchi Sea)