an empirical analysis of offshore service vessel utilization in the us gulf of mexico

An empirical analysis of offshoreservice vessel utilizationin the US Gulf of Mexico

Mark J. Kaiser and Brian SnyderCenter for Energy Studies, Louisiana State University,

Baton Rouge, Louisiana, USA

Abstract

Purpose – The offshore supply vessel (OSV) industry is critical to offshore oil and gas operationsaround the world and contributes to the economic and ecological impacts experienced by the localcommunities supporting the offshore oil and gas industries. The OSV industry has not been studiedsignificantly and the economic and ecological impacts to local communities is generally unknown.This paper aims to address these issues.

Design/methodology/approach – In this paper, the authors review the activities and logisticalrequirements involved in offshore exploration and development with special attention paid toworkflows and the manner in which service vessels are utilized in the Gulf of Mexico. The authorsestimate the OSV needs per stage of activity for offshore operations based on data collected fromcompany planning documents, fleet utilization data from oil and gas companies and service providers,interviews and surveys. The statistical data is synthesized and reconciled and despite large variancesthe data sources are in reasonable agreement. Empirical data on circuit factors are also provided. Theapplications and limitations of the analyses are discussed.

Findings – In the US GOM, a large variety of marine vessels transport goods and provide services toexploration, development and production activity. OSVs provide a vital link between offshore E&Pactivities and shore-based facilities. Offshore oil and gas operations cannot function without them andtheir utilization and spatial distribution provide a way of understanding the impacts of the offshore oiland gas industry on coastal communities.

Originality/value – This is the first empirical analysis of any offshore service vessel industry. Thedata presented here can be used to predict the environmental, economic, public health, andinfrastructural consequences of alternative offshore development policies.

Keywords Maritime structures, Vessels, Ecology, Offshore construction works,United States of America

Paper type General review

1. IntroductionOffshore supply vessels (OSV) are an important part of oil and gas operationsworldwide and in the Gulf of Mexico (GOM). The offshore service industry providesgoods and services to offshore activities. These services involve moving personnel to,from, and between offshore installations and rigs; delivering supplies, equipment, fuel,water, and food; towing rigs and placing and retrieving rig anchors; and supportingoffshore construction projects. Although each operation is unique and job specific, thereis also a commonality to all offshore activity, whether it occurs in the GOM or any otheroffshore basin worldwide[1]. Supply vessels support all exploration and productionoperations including exploration, development, production, and abandonment.

The current issue and full text archive of this journal is available at

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Received 26 June 2009Revised 7 January 2010Accepted 2 February 2010

International Journal of Energy SectorManagementVol. 4 No. 2, 2010pp. 152-182q Emerald Group Publishing Limited1750-6220DOI 10.1108/17506221011058687

The logistics of offshore oil and gas operations are critically important to theirsuccess, but have not been widely addressed in the academic literature because of thecomplexity of the operations and the difficulty of correlating service vessel use tooffshore activity. Academic study of offshore logistics has focused on quantitativemodels of ship and helicopter movement (Romero et al., 2007; Aas et al., 2007; Fagerholtand Lindstad, 2000; Gribkovskaia et al., 2007), fleet design (Aas et al., 2009),information management (Hull, 2002; Holland et al., 2005), outsourcing decisionmaking (Aas et al., 2008; Finch, 2002), sustainability (Matos and Hall, 2007), marketbarriers (Cairns and Harris, 1988), spatial issues (Parola and Veenstra, 2008; Fremont,2007; Ahmed and Miller, 2007) and facility siting policy (Gale and Albright, 1993;Randle, 1981; Price, 1987). The study of the logistics of the upstream offshore industryhas been diverse, but not theoretically unified or well developed. Empirically supportedmodels and analysis have also not been pursued. As a result, the number of OSV tripsneeded to support a specific type of activity is not known. This basic information isnecessary for addressing a variety of academic, planning and policy issues and is themotivation for this work.

On the USA outer continental shelf[2] (OCS), mineral resources are administered andleased to exploration and production (E&P) companies by the Minerals ManagementService (MMS), a branch of the Department of the Interior. The MMS is required toconduct environmental studies to assess the impact of oil and gas development on thehuman, marine, and coastal environment of affected OCS and coastal areas. As part ofthese Environmental Impact Statements, the MMS estimates the number of servicetrips that arise from shore and their socioeconomic impact (for further details, see theAppendix).

The offshore logistics network in the GOM is a complex and dynamic system with adiverse collection of work activities performed by hundreds of contractors across abroad time and space continuum (Figure 1). Durations of involvement range fromtransitory to short-term to time horizons that extend into decades. Activities occur over

Figure 1.Primary E&P related

shorebases in the GOM

Texas

Freeport

Aransas

Port Isabel

Galveston

Sabine CameronNew Iberia

Morgan CityHouma

Fourchon

Venice

Theodore

MississippiLouisiana

Intracoastal/freshwater

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all possible spatial dimensions from point activities to large one and two-dimensionalregions (installing pipeline and seismic surveying). Many system components and workprocesses vary with water depth and have evolved with changes in technology andbusiness arrangements. Hundreds of operators and service companies operate in theGulf and have the option of using a variety of shorebases and vessel types to servicetheir activity.

The level and frequency of onshore support (labor and material requirements)depends upon the life cycle stage of the work activity (e.g. exploration and production),the type of activity (e.g. sidetracking a well and installing flowline), site characteristics(e.g., location, age, facility type, production level and type, maintenance schedule), theoccurrence of exogenous events (e.g. hurricane activity, oil spills and recovery, accidents),and other factors. Some activities are essentially self-contained, in which the workactivity does not require – or requires only a minimum – of onshore support during theexecution of the activity. Seismic surveying and site clearance and verification areexamples of activities that require minimal onshore support. Installation, drilling andproduction operations occur over longer time horizons with more substantial materialrequirements, involving regular and frequent onshore support.

OSVs are known as the “workhorse” of the industry and the “trucks” of the ocean,while crewboats mainly function to transport personnel to and from manned platformsand rigs. OSVs and crewboats comprise the majority of the marine vessels in the GOMand are the focus of this paper.

OSVs are designed to carry a wide variety of cargo, utilizing space both above andbelow deck to carry supplies. With its wide-open bay (“well”) astern, high bow andforward accommodation, the OSV is ideally suited for the storage and delivery ofcontainers, drill pipe, tubing, anchors, and other heavy and oversized equipment(Plate 1). Below deck, a refrigerated cargo hold and special-purpose tanks facilitates thetransportation of food, drinking or industrial water, diesel fuel, drilling fluids, mud,cement, methanol, and other material. OSVs generally range from 160 to 260 feet inlength and travel at 10 to 12 knots (Aas et al., 2009).Crewboats are used to transport crews between offshore installations or near-shorelocations. Crewboats are smaller than OSVs and range in size from 75 to 190 feet (Plate 2).Older crewboats (circa 1980s build) are typically 100-120 feet in length, while newercrewboats are generally larger, 130-165 feet in length, travel at greater speed with morecargo carrying capacity (Barrett, 2008). New generation crew boats called fast supplyvessels can also carry a limited amount of supplies in addition to transporting crews.

The utilization of OSVs varies depending on the needs and size of the contractingcompany. Therefore, generalities on the use of OSVs is difficult. There is no single mostreliable source of data to estimate OSV needs. Ideally, a random subsample of OSVoperating companies categorized by developmental activity and containing detailedinformation on the activities of ships engaged in support of each developmental stagewould be collected; the data would cover at least one year and would be spatially diverseincluding both shallow and deepwater regions throughout the GOM, and it wouldinclude a heterogenous mix of operators from small independents to super-majors. Nosuch data source is publicly or commercially available. Therefore, it was necessary tocollect and analyze a variety of diverse data sources and to synthesize and reconcile theresulting information. We reviewed company plan data, conducted interviews and

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Plate 2.M/V Dyan JNote: A 100 feet crewboat

Source: Photo by Authors

Plate 1.The Harvey ProviderNote: A 240 feet OSV

Source: Harvey Gulf International


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surveys, and acquired detailed information from several E&P companies and one OSVcompany on their fleet use.

The purpose of this paper is to assess average patterns of OSV use during differentphases of oil and gas development in the US sector of the GOM. We quantify the numberof trips per week needed for drilling, development, production, and decommissioning.We begin with an overview of the work processes and vessel requirements across theprimary stages of E&P activity. We analyze several independent sources of data on OSVutilization and compare the utilization estimates. Special attention is paid to thelimitations of the analysis.

2. E&P life cycle stageBroadly speaking, four stages of E&P activity are commonly identified:

(1) exploration;

(2) development;

(3) production; and

(4) decommissioning.

The search for oil and gas begins with exploration. Development represents a transitionalstage between exploration and production. Abandonment is the end state where the wellsare plugged and infrastructure removed and the site returned to pre-lease conditions.

Various activities occur within each of the main stages, and within each subcategory,a variety of applications are found with activities that overlap and marine vesselrequirements that differ in magnitude and timing. The objective of this section is toprovide a summary overview of the activities and logistical requirements involved inoffshore E&P with special attention paid to work flows and the manner service vesselsare utilized. This discussion is meant to highlight the work processes and vesselrequirements across each of the main stages of operation and not as a comprehensivesurvey of offshore activity.

2.1 ExplorationThe objective of exploration is to find oil and gas reservoirs that can be commerciallydeveloped. The two primary types of field activity that occur during explorationinclude geophysical surveying and exploration drilling.

Geophysical surveying. Seismic operations often take place at the front end of theexploration process, and as a field is developed, crews may revisit the area for shortperiods of time. Geophysical seismic surveys are performed to obtain information onsurface and near-surface geology and on subsurface geologic formations. Seismicsurveys collect data on surficial geology used to identify potential shallow geologichazards for engineering and site planning. Most operations are reasonably selfsufficient and only require helicopters for crew change and minimum marine vesselsupport. Work rotation schedules of five weeks on/off mean that flights to the vesselare infrequent.

Exploratory drilling. Exploration drilling activities are conducted by contractorsoperating under the supervision of a leaseholder/operator. Exploration drilling maylast from several weeks to a few months in duration per well, and more than one wellmay be drilled at location. Exploration wells may be drilled from existing platforms,

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but most are drilled from mobile offshore drilling units (MODUs) such as jackups,semisubmersibles, or drillships.

Rigs require a steady stream of material when drilling a well, due to the physicallimits on the amount of material they can store. Modern drillships are able to storelarge quantities of equipment and materials, and require significantly less logisticalsupport than rigs and semisubmersibles, which must be supplied by service vessels orrisk shutting down operation. Generally, one or more dedicated OSVs are contracted tomaintain rigs in operation for the duration of the activity, and afterwards, are releasedto the market to find another contract.

Jackups and semisubmersibles generally require seagoing tugs for towing betweendrillsites and for location during mooring and unmooring operations. While manysemisubmersibles have on-board thrusters to assist, most rely on a spread mooringsystem for maintaining position during drilling. Anchor handling, towing, and supply(AHTS) vessels (Plate 3) tow rigs from one location to another and are equipped withpowerful winches to lift and position the rig’s anchors. AHTS vessels may arrivedirectly from an onshore base, or if in the field, from another job.

2.2 DevelopmentIf the results from exploratory drilling appear promising, additional wells will bedrilled to delineate the field and development wells drilled for production. Productionfacilities are designed, fabricated, and assembled in yards throughout the world, and

Plate 3.Normand MasterNote: A 267 feet AHTS

Source: GNU free documentation license


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then transported to site. Geophysical surveys are carried out to support developmentdrilling and the location and installation of production facilities and pipelines. The timeneeded to design, construct, and install the physical infrastructure to producehydrocarbons may be as little as six months or less for a caisson (one well system withflowline) to two years for a major platform to a decade or more for deepwater systemswith subsea wells. The duration of installation may range from a few weeks to severalmonths, depending on the complexity of the system components.

Structure installation. In shallow water, caisson and fixed platform installationshave well-established time tables because of the similarity and maturity of designconcepts. In deepwater, a variety of different structural elements exists which requiredifferent methods of transportation and installation. Deepwater fields are developed ona stand alone basis, as a central processing (host) platform, or as a satellite field tiedback to a host platform. The well system and drilling operations are functionallysimilar to shallow water and onshore, but systems and installation procedures arestructurally different.

The spatial relationship between system components and construction equipmentselection will influence the timing and sequence of activities. Details of installationschedules will vary, especially when the same construction equipment is selected fordifferent activities, but the overall effort will likely by similar. The activities associatedwith drilling, completion, and hookup of subsea wells are essentially the same as thoseassociated with exploration drilling.

Pipeline installation. Oil and gas is transported by a system of pipelines from thepoint of extraction to the point of consumption. The amount and type of supply, thenature of its decline, and the potential for nearby discoveries, as well as the environmentand distance over which fluids have to be transported, determine the design of thesystem. Three type of pipelines are utilized: gathering systems, tie-ins, and trunklines.Gathering lines are typically short segments of small diameter pipelines that transportmaterials from one or more wells to a production facility or from a production facility toa trunkline. Trunklines are typically large-diameter pipelines that transport productionfrom many wells and several fields to shore. Pumps and compressors add energy to thefluid to ensure that it will flow to its destination or the next pumping or compressionstation.

Pipelaying methods depend on environmental conditions[3], availability and cost ofequipment, length and size of line, water depth, and constraints of adjacent lines andstructures (Gerwick, 2007). The most common techniques include the S-lay barge,bottom-pull method, reel barge, and J-tube from platform. The operations, sequence ofactivities, duration, equipment, and vessel requirements vary with each technique.Before pipeline is layed, bathymetric and side scan sonar surveys are required to avoidcolliding with reefs and other seafloor disturbances. Rate of progress depends on thelay barge type, crew experience, and weather. The longer the barge, the greater thenumber of welding stations, and the faster the progress. Lay barges have limitedcapacity to store pipe and so pipe must be loaded regularly from the shore, transportedto site, and unloaded. In moderate sea states, a barge can be tied off alongside the laybarge, but in heavier sea states, supply boats are used.

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2.3 ProductionAfter the support structure and topsides equipment is installed and commissioned,production may last from a few years to several decades. For a manned facility,essentially all future activities will be confined to the platform. The frequency ofsupply boat visits will vary depending on the amount of production and the age of thestructure but once per week during normal operations is typical. More frequent visitsnormally occur during initial startup, drilling activities, equipment changeout, andworkover operations. For unmanned platforms and satellite developments, supplyboats will make periodic visits to provide logistical support, often once or twice a week,or on an as-needed basis depending on the level of automation and maintenancerequirements. Helicopters are also frequently used to transport crews to unmannedfacilities for inspection and repair.

Drilling, completion, and workover activities associated with subsea tiebacks arecarried out from MODUs, which may stay on location for periods ranging from a fewdays to several weeks, depending on the nature of the operation. Subsea maintenancework on wellheads or other subsea components will require mobilization of a drillingrig or other construction vessel. The duration of these activities will vary widely, butthe equipment and nature of the operations are similar to exploration drilling andinstallation activities. Workover operations can be performed in many different waysusing different vessel types.

2.4 DecomissioningOnce the facility stops production and ceases to serve a useful purpose, the site will beabandoned and the lease will revert to the government. Decommissioning is a highlyprescribed process which begins when notice is given that the lease has ceasedproduction. An operator has six months to notify MMS when production has ceased ona lease, and from the point of notification of cessation of production, the operator hasone year to clear the lease of all facilities. The nature of the activities and the equipmentinvolved in abandonment are generally similar to those involved in installation butrequire less time.

Wells will be plugged and abandoned in accordance with federal regulation, andperformed using a wire-line unit, drilling rigs, workover rigs, or coiled tubing units. Ina typical removal operation, a heavy lift vessel arrives at site and AHTS vessels set upanchor. Cargo barges are towed to site to accept the deck and jacket structure. Removaloperations follow the installation process in reverse. Cranes lift the deck in one or moresections and secures the load to a cargo barge. The jacket is lifted and removed fromthe seabed, and the deck and equipment is transported to an onshore fabrication yardor storage facility. The jacket can be taken to shore for storage or scrap, taken to adesignated reef site, or topped in place. After the platform is removed, the area iscleared of debris and clearance is verified with specially equipped trawlers with nets.Debris from around the platform site is cleared and sent to shore for disposal.

Selection of equipment and procedures employed in decommissioning depend onmany of the same factors that influence selections for installation, includingavailability and cost. The duration of work will usually range from two or three weeksfor removal activity. As in the case of installation, certain decommissioning activitiescan be carried out simultaneously.


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3. Data sourcesOSVs are usually assigned to either a drilling or production pool with boats in theproduction pool under long-term contracts (perhaps six months to a year) and boats inthe drilling pool on shorter term (approximately three months) contracts. Larger E&Pcompanies may contract several boats and use them as a pool among severalproduction projects whereas smaller companies are likely to use a dedicated boat.Often, a manned production platform is linked to several nearby wells protected bycaissons and well protector structures. The OSV first visits the manned platform andover the course of the day may ferry men and supplies to the nearby fields.

The data sources used and their reliabilities in terms of “completeness” and“accuracy” are summarized in Table I. Completeness refers to the ability of the data toestimate activity throughout the GOM and the extent to which the data is biased bysmall sample size. Accuracy refers to the probability that the data is correct in itsindividual estimations. For example, the BP data is considered to have poorcompleteness due to its focus on deepwater activities, but good accuracy since webelieve it to be an accurate measure of all trips in its sample. The data sources listed inTable I and their varied strengths and weaknesses are described in detail later.

There are two main classes of data analyzed: data from MMS plans and dataprovided by companies. Plan data describes the activity that the operator expects tooccur in a particular development; company data describes actual operational data.Individually, while not particularly informative, taken together they provide areasonable representation of OSV activities. While none of the collected data meets allthe criteria of an ideal data source, the plan and BP data are of relatively long temporalduration, the plan data is spatially diverse covering the entire GOM, the BP and

Dataname Data source Completeness Accuracy Limitations

Reasonableapplications

Simpledata

MMS DOCD andEP plans

Good Poor Requiresassumptions ondevelopmentalstage

Drilling andproduction

Detaileddata

MMS DOCD plans Good Medium Reports engineeringestimates, notactual movements

Production, drilling,and construction

Apache Apache ship usedata for first fourmonths of 2008

Medium Medium Covers onlyFourchon and onlyfirst four months ofyear; no production

Drilling,construction,and P&A

BP BP ship use datafor 2008

Poor Good Primarilydeepwater activity

Deepwaterproduction

C-Logistics

Ship use data froman OSV operator

Medium Good Primarilydeepwater drillingdata

Deepwater drillingand both shallowand deepwaterproduction

Interview Interviews withindustryparticipants

Poor Medium Only interviewedsmall sample oftotal industryparticipants

Check onreasonableness ofother estimates

Table I.Data sources and theirrelative quality

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C-Logistics (CL) data are deepwater focused, and the BP and Apache data include anumber of developmental phases including abandonment.

There are other sources of marine commerce data available, including data from theArmy Corps of Engineers and the automatic identification system (AIS), which trackship movements using surveys and transponder signals. These data sources are notuseful for determining the number of vessels used for a particular developmentalactivity, and only provide information on vessel movements without reference to oiland gas developmental stages.Throughout the paper we generally refrain from detailed statistical analyses oradvanced methodologies in favor of reporting means and standard deviations. Wechoose to do so for two reasons. First, the variances in the data are generally very largerelative to the means, making statistical analyses uninformative. Second, the paper isintended to provide base and explanatory data, not to test hypotheses or buildsophisticated models on relative OSV usage.

4. Plan dataWhen E&P companies plan to undertake activities in the GOM (exploratory ordevelopmental drilling, well completion, construction and installation, pipelineinstallation, and commencement of production) they are required to complete either anexploration plan (EP) or a Development and Operations Coordination Document(DOCD). EP plans are required for exploratory drilling, while DOCD plans are requiredfor developmental drilling, installation, and commencement of production.

In some cases, plans report detailed information on the number of days and hoursvessels are expected to be operating in the GOM. However, not every plan is required tosubmit detailed information on vessel activity. Table II shows a checklist of questions

(A) Emissions worksheets and screening questionsScreen procedures for DOCD’s Yes No

If any calculated complex total (CT) emission amount (tons) associated withyour proposed development activities more than 90 percent of the amountscalculated using the following formulas: CT ¼ 3,400D2/3 for CO, andCT ¼ 33.3D for the other air pollutants (where D ¼ distance to shore inmiles)? XDo your emission calculations include any emission reduction measures ormodified emission factors? XDoes or will the facility complex associated with your proposed developmentand production activities process production from eight or more wells? XDo you expect to encounter H2S at concentrations greater than 20 parts permillion (ppm)? XDo you propose to flare or vent natural gas in excess or criteria set for theunder 250.1105(a)(2) and (3)? XDo your propose to burn produced hydrocarbon liquids? XAre your proposed development and production activities located within25 miles (40 kilometers) from shore? XAre your proposed development and production activities located within124 miles (200 kilometers) of the Breton Wilderness Area? X

Source: MMS DOCD plan

Table II.Sample screening

questions from DOCDplans


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that must be answered in EP and DOCD plans. If the E&P company answers any ofthese questions affirmatively, then they must submit a detailed account of the numberof operating vessels and the number of days and hours per day those vessels areoperating by activity. This data is referred to as “detailed data” and Figure 2 is anexample of the form E&P companies must complete. If the E&P company answers noto all the questions listed in Table II, then they only have to report the number of crewand supply vessel trips per week without reference to the stage of development duringwhich the trips are occurring. We refer to this data as “simple data”; Table III providesan illustration of a sample table. Companies that provide detailed data are required toprovide the simple data that all companies must provide. Therefore, plans contain twotypes of potentially useful and ambiguous information on the number of OSV trips.

Figure 2.Example of the form thatmust be completed inDOCD plans by E&Pcompanies

Source: MMS DOCD Plan

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The first EP and DOCD plans a company submits are referred to as initial plans. Asplanning evolves and changes, operators submit supplemental and revised plans. Asupplemental plan is a revision to an approved plan that proposes the addition of anactivity that requires a permit. A revised plan is a revision to an approved plan whichproposes changes such as the location of a well or onshore service base. Supplementalplans may contain two kinds of detailed data, aggregate data on total plan emissionsand data on only the supplemental plan emissions. We used only the supplementalplan emissions data with the supplemental plan activities and did not use the totalaggregate emissions. This allowed us to use both supplemental and initial planswithout fear of double counting trips.

Trip data from both the simple and the detailed data are estimates made byengineers and do not reflect the actual number of trips. They are often considered to beconservative estimates so that if errors in emission estimates are made the emissionsare overestimated rather than underestimated. The estimates are stated in the plansnot in terms of the number of trips, but the number of days vessels will be needed[4].Unless otherwise stated, we assume that for the simple and detailed data the number ofdays boats are needed is equivalent to the number of times a boat leaves port and theterms boat days and trips are used interchangeably. As a result, the plan data mayoverestimate the number of trips but this can be corrected for by the use of circuitryfactors, discussed later.

4.1 Simple dataThe simple data in DOCD and EP plans usually report only the number of days supplyand crew boats are needed but does not report the operational phase for which theseboats are needed. We analyzed simple data collected from 1,261 DOCD and EP plans.This dataset included all plans filed from January 2005 through July 2008 and arandom subsample of 50 plans per year from January 1, 2001 to December 31, 2004.The data set does not include duplicate plans which are filed when a lease containsmore than one area block.

OSV trips. Comparing the number of trips reported in the simple data with thenumber of trips reported in the detailed data showed that simple data table numberswere generally the maximum number of trips needed over the multiyear period theplans covered. This makes analysis of the simple data difficult because plans containmultiple activities (pipelaying, drilling, and production) and we do not know whichperiod the reported simple data represents. Therefore, we categorized the 1,261 plansaccording to whether they contained drilling, construction, or pipelaying activities andanalyzed the OSV requirements within each category (Table IV).

TypeMaximum fuel tank

storage capacity (bbls)Maximum numberin area at any time

Trip frequencyor duration

Supply boats 500 1 Once a weekCrew boats 500 1 Once a weekAircraft 1,900 1 As needed

Note: This is the basis of the simple data used in the analysisSource: MMS DOCD plan

Table III.Sample table

from DOCD plans


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The standard deviations are large and roughly the size of the means. The first row inTable IV in which there is no construction, drilling or pipe laying represents thoseplans in which the E&P company sought to commence production. The values of 1.9crew boats per week and 1.8 supply boats per week are considered to be the averageneeds during production.

The sixth row of Table IV in which construction and pipe laying do not occurrepresents the number of vessels needed during drilling. This assumes that E&Pcompanies report the maximum number of boats needed at any one time and thatdrilling requires more vessels than production. That is, it assumes that when a plancontained both drilling and production, the OSV needs from drilling were reported.

Limitations of simple data. The simple data is a large data set that is potentiallyinformative but has limitations. Simple data does not refer to which stage ofdevelopment the data describe and as a result assumptions linking developmentalphase and OSV data must be made. Despite this limitation, however, the mean crewand supply boat usage agree relatively well. For example, the crew and supply boatneeds in the first four rows of Table IV (in which drilling does not occur) are allrelatively constant at around two boats per week. Similarly, the data in the next fourrows in which drilling occurs suggest about four crew boats and three supply boats areneeded per week. This consistency among differing plan types suggest that theaverages for plans with drilling and plans without drilling (“no drilling total” and “withdrilling total” in Table IV) may be good estimates of OSV needs during drilling andproduction.

The simple data covers a long time span including several active hurricane seasons,the ongoing responses to the destruction caused by these hurricanes, low oil prices of2001 through 2003, and the very high prices of 2006 through 2008. The data does notcapture any time dependency or directly reflect such environmental conditions since,as mentioned previously, they are estimates of expected activity as opposed to themeasurement of actual activity. The temporal duration generates a large sample sizeand reduces the potential impact of aberrational reporting on overall estimates.

Drilling Construction Pipelines Activitya Crew boat Supply boat Sample size

N N N Production 1.9 (1.9)b 1.9 (1.8) 81N N Y Pipelines 2.6 (1.2) 2.5 (2.0) 21N Y N Unclear 1.9 (2.2) 1.8 (1.6) 96N Y Y Unclear 2.1 (1.9) 1.8 (1.4) 65No drilling total Unclear 2.0 (2.0) 1.8 (1.7) 263Y N N Drilling 3.5 (2.1) 3.3 (1.8) 448Y N Y Unclear 4.1 (3.1) 2.9 (1.7) 10Y Y N Drilling 4.0 (2.5) 3.3 (1.8) 438Y Y Y Unclear 3.7 (2.1) 3.0 (1.5) 102With drilling total Drilling 3.8 (2.3) 3.3 (1.8) 998

Notes: aActivity means the developmental stage, we assume the data generally represents; this isbased on the assumption that simple data reports the maximum number of trips needed over all of theactivities included in the plan and that drilling requires more OSV use than production; bstandarddeviations in parenthesesSource: MMS DOCD and EP plan simple data

Table IV.Average crew and supplyboat needs in vessel tripsper week

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4.2 Detailed dataA total of 311 DOCD plans were reviewed for information on the number of servicevessels required in offshore E&P activity. The 311 plans represent every DOCD planfiled between October 1, 2006 and October 1, 2008. The data set includes supplementalplans but not duplicate plans. Of the 311 plans, 220 reported some type of detailed data.

Drilling. Out of the 311 plans analyzed, only 95 contained both drilling and detailedinformation on the number of vessels needed. We determined average water depths forthese 95 plans, summed the numbers of vessels needed across years to determine atotal number of vessels needed per well, divided the number of vessels by the numberof weeks spent drilling and the number of wells drilled to determine the number ofvessels used per well per week and then subdivided into shallow (less than 1,000 feetwater depth) and deepwater (greater than 1,000 feet water depth) categories. Thesedata are presented in Table V. As expected, the duration of drilling and supply vesselneeds are greatest in deepwater, however, crew boat use declines in deepwater drilling,likely due to the use of helicopters to ferry personnel and utilization of larger boats.

Development. Construction support data is more complex than the other dataanalyzed due to the different types of construction. Table VI depicts basic informationon construction data. On average, it takes about ten days to install structures in theGOM: 13 days for platforms, nine days for caissons.

Out of the 311 plans reviewed, 181 included some construction. Of these 181 plans,84 did not report specific vessel movements. Furthermore, many of the plans includedvessel information for the installation of more than one type of facility (for example, acaisson and production facilities). We removed these plans from the analysis becausewe could not determine which boats were needed for which type of constructionactivity.

Water deptha Time per well (days) Supply vessel Crew boat Tug

Shallow 54.6 3.6 (1.0)b 3.2 (0.3) 0.4 (0.1)Deep 74.7 6.0 (1.2) 2.9 (0.4) 0.5 (0.1)Total 56.9 3.9 (1.0) 3.1 (0.3) 0.4 (0.1)

Notes: aShallow water is defined as water depth less than 1,000 feet; deepwater is defined as waterdepth greater than 1,000 feet; bstandard deviations in parenthesesSource: MMS DOCD plan detailed data

Table V.Average number of days

vessels are needed perwell drilled and trips per

week per well by waterdepth

Number of plans with construction 181Number of plans with construction but without detailed data 84Number of plans for platform construction 81Number of plans for production facilities construction 42Number of plans for caissons construction 71Number of plans for satellite structure construction 9Number of plans for subsea wellheads/manifold construction 33Time to install platforms (days) 13.1Time to install caissons (days) 9.3

Source: MMS DOCD plan detailed data

Table VI.Basic information on

detailed construction data


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Table VII shows the number of boats needed for the installation of caissons, platforms,satellite structures, and subsea manifolds. Assuming platforms require 13 days onaverage to install and caissons take on average nine days to install, then about 0.7 OSVsare needed per day for platform installation and about 0.6 are needed per day for caissons.The DOCD plans did not contain information on the duration of satellite or subseamanifold construction duration and can only be analyzed on a per installation basis.

Production. Unlike other stages of development, production is primarily associatedwith crew boat and supply boat activity. In the DOCD plans, data on the number of OSVtrips are split into two or more calendar years with the total number of trips reported foreach year. If the first year of data is incomplete because production is scheduled to startafter the first calendar year has already begun[5], then we assumed that data from thesecond year was a better estimator of the number of OSV trips needed and used it in theanalysis. Of the 311 plans reviewed, 192 contained information on the number of OSVtrips during production. Table VIII shows the number of trips required per week duringproduction per developed structure and per well drilled.

We examined OSV needs by water depth by dividing the sample into shallow (lessthan 200 feet), intermediate (200 to 1,000 feet), and deepwater (greater than 1,000 feet)categories. The production needs by water depth are shown in Table IX. Table IXshows that crew boat needs are greatest at intermediate depths and that supply boatneeds increase with increasing depths. This is due to the fact that helicopters are amajor mode of transportation for deepwater structures.

We also examined the differences in OSV needs during production by structuretype. Table X shows the results of the analysis. Many of the sample sizes are small[6]making statistical analyses ambiguous. Caissons and well protectors require thefewest number of vessel trips. Although sample sizes were small, spars requiredthe greatest number of trips in support of production. This could be due to the large

Platforma Caisson Satellite structure Subsea manifold

Derrick barge 9.3 (5.4)b 10.5 (12.8) 17.3 (19.9) 32.7 (52.3)Tug 6.8 (5.5) 7.8 (13.6) 13.0 (22.8) 11.0 (14.9)Supply 4.2 (5.9) 2.8 (4.3) 4.5 (9.0) 110.7 (171.3)Crew 4.8 (5.9) 2.8 (4.1) 4.5 (3.1) 0 (0)OSV total (crew þ supply) 9.1 (8.8) 5.6 (7.9) 9.0 (10.4) 110.7 (171.3)

Notes: aSample size is 30 for platforms, 28 for caissons, four for satellites, and three for subseamanifolds; bstandard deviations in parenthesesSource: MMS DOCD plan detailed data

Table VII.Average boat daysneeded for installation ofproduction platformsand caissons

Per developed structure Per well drilled

Crew 0.9 (1.7)a 0.6 (1.3)Supply 1.8 (2.3) 1.3 (1.9)Total 2.7 (3.0) 1.9 (2.6)

Notes: Sample size ¼ 192; astandard deviation in parenthesesSource: MMS DOCD plan detailed data

Table VIII.Average number of tripsper week per developedstructure and per welldrilled needed forproduction

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production volumes and personnel demands on deepwater structures which couldnecessitate more frequent vessel support.

Pipelines. Of the 311 plans, 122 included plans for pipeline construction and 83included detailed information on the number of service vessels needed. Table XI depictsthe per installation number of days bury and lay barges, supply boats, crew boats, andother support vessels are needed. Summing the crew and supply vessel needs per daygives a value of 0.43 OSVs per day during pipeline installation. We also analyzedsupply and crew boat needs per mile of pipeline installed. These data are also shown inTable XI. When the number of vessels needed is divided by the mileage of pipeline to beinstalled, the standard deviations increase considerably. Thus, the number of vesselsneeded per individual pipeline installation will probably be more informative as anestimate of OSV needs than the number of OSVs needed per mile of pipeline.

Limitations of the detailed data. The detailed data reported here are biased by thefact that not every plan is required to submit data on vessel needs. MMS uses achecklist to determine if a plan is required to specify their per vessel emissions

Structure type Crew boat Supply vessel Total OSV Sample size

Caisson 0.8 (1.8)a 1.5 (2.1) 2.3 (3.5) 58Fixed 1.1 (1.7) 2.0 (2.6) 3.1 (3.4) 79Well protector 0.0 (0.0) 0.2 (0.4) 0.2 (0.4) 9Subsea manifold 0.3 (0.6) 2.0 (1.7) 1.8 (2.1) 3Spar 1.8 (3.5) 3.5 (2.5) 5.2 (6.0) 4Other (TLP, CT) 0.0 (0.0) 2.5 (3.1) 2.5 (3.1) 4

Notes: Values are in boats per week; astandard deviations in parenthesesSource: MMS DOCD plan detailed data

Table X.Average OSV needs

during production byproduction platform type

Water depth (feet) Crew boat Supply vessel Sample size

,200 0.8 (1.6)a 1.7 (2.4) 147200-1,000 1.3 (1.9) 2.0 (2.0) 30.1,000 0.8 (1.9) 2.4 (2.2) 15

Note: aStandard deviations in parenthesesSource: MMS DOCD plan detailed data

Table IX.Average number of trips

per week duringproduction (per structure

installed) by boat typeand water depth

Lay barge Support vessels Bury barge Crew boat Supply boat

Per pipeline installedAverage (SD) 12.6 (17.3) 15.6 (21.0) 4.2 (7.4) 1.6 (3.9) 3.7 (7.7)Average per week 6.4 7.9 2.1 0.8 1.9

Per mile of pipelineAverage (SD) 27.5 (115.3) 32.1 (122.2) 6.2 (30.3) 0.6 (1.4) 4.5 (27.5)Average per week 14.1 16.4 3.2 0.3 2.3

Source: MMS DOCD plan detailed data

Table XI.Data on pipeline

construction supplyneeds per pipeline

installation and per mileof pipeline


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(recall Figure 1). If a plan answers “yes” to any of the questions on the checklist, theyare required to detail their vessel activity. The most common reasons a plan mustdetail its vessel activities is an affirmative answer to either of the last two items.Therefore, the DOCD plan data is believed to be biased towards shallow water plans[7].

Additionally, the detailed data only reports the number of days a vessel is requiredto be operational in support of activities. It does not actually report the number of tripsor times a vessel enters or leaves port. It is possible that OSVs may visit many leasesites in a single trip which could result in an overestimation of vessel trips, especiallyduring production.

The detailed data only includes information from DOCD plans. As a result, itincludes very little information on exploratory drilling. Exploratory drilling OSV needscould differ from needs during developmental drilling, potentially biasing the data.

Plan data is also thought to overestimate trips due to the conservative nature of thedata. Interviews with E&P company personnel and consultants suggested thatcompanies may input the maximum number of trips they believe they would need sothat if there is a mistake they overestimate, rather than underestimate, the plannedemissions. Again, this could lead to inflated trip estimates.

5. Apache dataApache’s Fourchon operations center provided activity logs for a four month periodfrom January 2008 through April 2008. The logs recorded every time a vessel wasloaded or unloaded and included the vessel name, the date and time, the rig or platformlocation. These logs were matched with additional data on the activities at each rig orplatform and the vessel type (crewboat, utility, or supply) to create a dataset thatconsisted of the vessel name, date of trip, location, and activity at location. Activitiesinvolved included drilling, plugging and abandonment, and construction.

5.1 DrillingInformation on the service vessels used to supply ten rigs over a four month period wasanalyzed. In total, OSVs made 1,403 trips to these ten rigs over the 115 days fromJanuary 1, 2008 to April 25, 2008. In many cases an OSV supplied or crewed more thanone rig per trip. Thus, the ten rigs actually required 1,946 visits from OSVs,predominately crew boats: 1,465 visits by crewboats, 461 by supply vessels, and theremainder (20) by mini-supply or AHTS vessels.

Table XII shows the average number of trips needed per day by both crew andsupply vessels and the total number of trips for all boat types. The ratio of the standard

Vessel Drilling Construction Plugging and abandonment

Utility 2.9 (2.2) 2.8 (2.8)Crew 10.5 (3.5)a 1.8 (2.5) 1.4 (2.1)Supply 3.5 (1.4) 0.2 (0.3) 1.4 (2.1)Mini-supply 0.35 (1.1)Total 14.0 (3.5) 4.7 (2.0) 5.9 (1.4)

Note: aStandard deviations in parenthesesSource: Apache data

Table XII.Average OSV needs intrips per week duringdrilling, construction, andplugging andabandonment

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deviation to the mean decreases when all boat types are combined which may reflectthe fact that supply boats can fill a limited crew boat role and vice-versa; therefore, thetotal number of boats used in drilling operations should have less variance than thenumber of trips of a specific boat type.

5.2 DevelopmentIn the Apache dataset, nine construction projects required 184 OSV trips, an average of20.4 trips per project. Owing to the relatively short duration of many constructionprojects, we believe that the data encompassed the entirety of at least six of the nineconstruction projects. Owing to the high variance on a per project basis, we divided thenumber of trips by the duration of activity. Table XII shows the averages and standarddeviations for different boats utilized. Again, the variance (as a proportion of the mean)decreases when the number of trips are totaled boat types. The majority of trips duringconstruction are by utility boats; 117 of the 184 trips were by utility boats. A total of 57trips were by crewboats and just 11 were by supply vessels. As in P&A operations,boats almost never visited more than one site per trip.

5.3 Plugging and abandonmentThe data on plugging and abandonment included 539 trips to 13 sites. It was not clearhow many, if any, of the P&A sites were both started and completed during the periodcovered by the data. Therefore, we converted all data into a measure of trips per day.Table XII summarizes the results. The majority of OSVs used during P&A operationsare supply vessels and utility boats. Supply vessels accounted for 217 of the 539 trips(40 percent); utility boats accounted for 173 trips (32 percent). Crewboats accounted for131 (24 percent) of trips, while mini-supply boats accounted for 18 trips (3 percent). Incontrast to drilling data, crewboats were responsible for 75 percent of activity.

5.4 CircuitryMost of the data described in this paper is in terms of visits by vessels to an offshorelocation. However, a vessel may visit more than one offshore location each time itleaves port. In order to forecast the total number of departures from port needed tosupport OCS activities, it is important to have information about the average numberof offshore locations a boat visits per embarkation. This is called circuitry (in industryparlance a “milk run”) and can be expressed quantitatively as the expected number ofvisits made per embarkation.

The Apache data allowed us to determine the number of times a ship left port andthe number of times it visited another GOM site without first returning to port. To

Vessel Drilling Construction Plugging and abandonment

AHTS 1 1Crew 1.6 1.1 1Mini supply 1 1 1Supply 1 1 1Utility 1 1.03 1Other/not reported 1.9 1 1

Source: Apache data

Table XIII.Circuitry factors by

activity type in Apachedataset


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estimate circuitry we added the number of times a boat left port to visit a GOM site tothe number of times the same boat visited another GOM site without first returning toport, and divided by the number of times a boat left port[8].

By definition, circuit factors are greater than or equal to one. A circuit factor of oneindicates a vessel dedicated to a specific activity, while a circuit factor greater thanone indicates multiple stops along the way. The circuitry factors for different vesseltypes in the Apache data are shown in Table XIII. Notably, only crewboats mademultiple stops during drilling operations, which does not seem to be representative ofthe OSV industry as a whole based on our interviews and related data.

5.5 LimitationsThe Apache data is limited by several factors. First, the data only covers a four-monthperiod from January through April. OSVs can only be used in favorable weather andthere can be seasonality in usage patterns. As a result, the data could be biased.Similarly, due to the relatively short duration of the dataset, the data could be censoredby the inclusion of incomplete events. This is especially true for drilling and P&A datawhich take a long time to complete. As a result, we may have data for only a portion ofa project and the OSV needs typically change during different portions of work flow.Furthermore, the dataset may not include information on rare but OSV intensiveevents that can occur over the lifetime of offshore developments, such as wellworkovers, repairs, or personnel evacuations. Finally, the Apache data only includesdata from the Fourchon operations center. Based on conversations with Apachepersonnel, we believe that the majority of trips associated with the projects studiedoriginated in Fourchon and were therefore in our data set. However, it is likely that atleast some OSV trips originated from other ports and were not included in the data.

6. BP dataBP provided data on GOM operations for all of 2008. The data consisted of over 68,000records on the activities and locations of 47 boats used throughout the year. In total, BPutilized 11,766 boat days split among 24 OCS locations 20 of which were deepwater.The total number of trips into the GOM recorded is 3,075. Of the 3,075 trips, 727 areclassified as being related to the continental shelf, 2,224 are described as deepwater,and 97 are related to pipeline construction. Trips by boat type are shown in Table XIV.

6.1 CircuitryThe average circuitry factors by boat class are shown in Table XIV. On average, eachtime a boat left port it visited 1.4 sites before returning. We separated boats into those

Boat type Total tripsAverage trips per boat

per weekProportion of total trips

(%)Average circuitry

factor

AHTS 76 1.5 2.5 1.5Crew 1,682 4.8 54.7 1.2Other 98 0.6 3.2 1.8Supply 1,219 1.1 39.6 1.5Total 3,075 2.2 100.0 1.4

Source: BP data

Table XIV.Average and total use byboat type in BP dataset

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used for deepwater operations and those not used for deepwater operations. The circuitryfactor for boats only used on the shelf was 1.13 (SD ¼ 0.20) while the circuitry factor forthose used only in deepwater operations was 1.55 (SD ¼ 0.75). This suggests that there isa difference in circuitry between shallow and deepwater operations with boats used indeepwater visiting more sites per trip than those used in shallow water operations.

6.2 Trips per production unitTable XV shows the distribution of trips by end location including both trips thatoriginated at a shorebase and those that originated at another location in the GOM. Onaverage among the 19 producing deepwater sites, 173 visits were made in 2008(SD ¼ 220.7). These 173 visits were associated with 116.6 trips into the GOM(SD ¼ 136.4). The number of trips is lower than the number of visits because a numberof boats visited more than one site per trip.

Table XVI depicts a more detailed picture of OSV operations in support ofdeepwater exploration and production broken out by total visits and vessel type. Thesum of visits from shore and visits following movement to another GOM location isdepicted. We classified 16 sites as either related to exploration and development orproduction. We removed three deepwater sites from consideration (Das Bump,Exploration, and Tamara) because of the limited number of OSV trips and the limited

LocationLeft port to

OCSIntra OCS

movementaTotal visits to

site Activity

Amoco Pipeline 97 46 143 PipelineTubular Bells 27 9 36 Deepwater explorationAtlantis 321 103 424 Deepwater productionEl Dorado 50 4 54 Deepwater explorationFreedom 77 25 102 Deepwater explorationHolstein 189 61 250 Deepwater productionHorn Mountain 41 58 99 Deepwater productionKaskida 58 2 60 Deepwater explorationKing 69 26 95 Deepwater productionKodiak 89 37 126 Deepwater explorationMad Dog 174 124 298 Deepwater productionMardi Gras 8 5 13 Deepwater pipelineMarlin 170 122 292 Deepwater productionNakika 127 42 169 Deepwater productionPompano 30 61 91 Deepwater productionPuma 11 2 13 Deepwater explorationThunder Horse 548 395 943 Deepwater productionWill K 227 2 229 Deepwater explorationWestern Shelf 80 2 82 Shelf P&A, platform

removal, etc.Eastern Shelf 647 43 690 Shelf P&A, platform

removal, etc.None listed 20 8 28Total 3,075 1,188 4,263

Note: aIntra OCS movements are movements in which a ship moves from one location on the OCSto another location on the OCS without first going to portSource: BP data

Table XV.Distribution of trips by

destination in BP dataset


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time over which these trips occurred. We determined the duration of activity at eachsite and the number of trips per week needed in support of exploration anddevelopment and production activities. The average OSV use for exploration anddevelopment was determined to be 4.36 (SD ¼ 1.69) trips per week and the utilizationduring production was 5.82 (SD ¼ 5.0) trips per week. The increased trip numberduring production was due in large part to the large number of trips needed to supportthe Thunder Horse production platform. Also notable is the much lower standarddeviation during exploration and development as compared to production perhapsindicating more regular vessel requirements.

Crew and supply boat needs among sites are relatively similar. During explorationand development crewboats were used slightly more than supply vessels while duringproduction supply boats were used slightly more than crewboats.

6.3 Continental shelf dataAlthough most of the data provided by BP was related to deepwater activities the dataalso included information on 727 trips into the GOM for shelf related activities and 45intra GOM vessel movements which were classified as shelf related. The shallow wateractivities were heavily biased towards decommissioning. Table XVII shows thedistribution of trips among ten locations. At five locations platform removal operationswere being conducted, and at three locations plugging and abandonment operationswere occurring. At one site a well intervention was ongoing. OSV needs during P&Awere greater than OSV needs during platform removal or abandonment. On average,during P&A operations 4.6 OSVs were needed (SD ¼ 2.54) per week for an average of

Total visitsto site Duration

Visits/week

Crewvisits

Supplyvisits

Exploration and drilling siteTubular Bells 36 116 2.2 1.1 0.8El Dorado 54 107 3.5 2.8 0.7Freedom 102 160 4.5 2.6 1.8Kaskida 60 99 4.2 2.8 1.5Kodiak 126 285 3.1 1.1 1.2Puma 13 14 6.5 3.0 3.5Will K 229 246 6.5 3.9 2.6Exploration and drilling average 4.4 2.5 1.7Production siteAtlantis 424 366 8.1 3.4 4.4Holstein 250 366 4.8 2.9 1.8Horn Mountain 99 366 1.9 0.7 1.2King 95 200 3.3 1.0 0.7Mad Dog 298 366 5.7 2.4 3.1Marlin 292 366 5.6 1.9 2.5Nakika 169 366 3.2 1.0 1.5Pompano 91 366 1.7 0.3 1.1Thunder Horse 943 366 18.0 7.0 10.3Production average 5.83 2.23 3.0

Source: BP data

Table XVI.Deepwater trips per weekby stage and boat type inBP dataset

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298 days (SD ¼ 53.5), while during platform removal an average of 0.43 OSVs wereneeded per week (SD ¼ 0.29) for an average of 119 days (SD ¼ 79).

6.4 Pipeline dataOnly two pipeline projects were contained in the BP data, the Mardi Gras pipeline andthe Amoco pipeline. The Mardi Gras pipeline included 42 days of data reportsincluding 13 trips (an average of 2.16 per week). Notably, all but two of these trips wereconducted by remotely operated underwater vehicle (ROV) boats; the other two wereby crew boats. The Amoco pipeline project contained information from the entire yearand required 143 trips (2.75 trips per week). In this case, 114 of the 143 trips wereconducted by crew and supply vessels (74 supply trips; 40 crew boat trips). A total of29 trips were by ROV support vessels.

6.5 LimitationsThe BP data provides a useful perspective due to its emphasis on deepwater activities,however, due to this emphasis care should be taken when extrapolating. Deepwateractivities represent a large fraction of GOM production but a small fraction of GOMinfrastructure and deepwater logistics. Furthermore, the shallow water data includedin the sample is not related to production or drilling, the activities represented in thedeepwater data; this makes comparisons between the data less meaningful. The BPdata does not provide information on the developmental stage of the production units.Deepwater development is complex and multiple developmental stages typicallyoverlap. For example, even though production is occurring from some wells, drilling orworkovers may be occurring simultaneously. If this occurred during 2008, we wouldnot be aware of it and would treat trips that may be in support of drilling as production.

7. C-Logistics dataCL is an OSV operator in the GOM and a division of Edison Chouest, one of the region’sdominant OSV companies. CL provided data on OSV use over an 18-month period fromlate May 2007 to late November 2008. The data contained records of 4,788 tripsconducted in support of drilling and production, vessel type, start and end shorebases,destination, tonnage, and activity.

Left port forOCS

Intra OCSmovement

Totalvisits Duration

Visits/week

GI 40 platform abandonment 6 2 8 161 0.3SM 260 platform removal 8 1 9 145 0.4WD70 and WD96 platform abandonment 5 5 10 84 0.8GI 32 platform removal and site clearance 4 0 4 205 0.1Average platform removal operations 148.7 0.4SM 205 P&A 139 2 141 271 3.6GI 95A P&A 373 17 390 360 7.5WD 94G P&A 96 10 106 264 2.8Average P&A operations 298.3 4.7

Source: BP data

Table XVII.Activities and OSV use

on continental shelflocations in BP dataset


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7.1 ProductionProduction data included information on 929 voyages conducted in support of theoperations of three supermajors. The average voyage took 2.5 days and boats oftenvisited more than one site. The distribution of trips by boat type is shown in Table XVIII.The dataset included information on fast supply boats and can be considered a type ofcrewboat. Average circuitry factors during production by boat type are shown in the lastrow of Table XVIII. Fast supply boats have a circuit factor near unity indicating they arededicated to a specific site. Crewboats and supply boats have a larger average circuitry,indicating a greater number of intermediate destinations. Boats visited between one andsix sites per trip.

The total number of visits per week were determined using the duration of activity ata particular site, that is, the difference in time between the first trip and the last trip at asite and not the overall duration. A summary by water depth is shown in Table XIX.Fewer trips were conducted per week for deepwater than shallow water activity.

7.2 DrillingCL data also included information on 3,858 voyages in support of drilling. Table XIXshows the number of trips per week during drilling by water depth. Shallow waterdrilling required slightly fewer trips per week than deepwater drilling; this potentiallydue to the large storage capacity of drillships which require infrequent replenishment.The distribution of trips by boat type is shown in Table XX. Drilling support includeda small proportion of AHTS trips which did not occur during production. The averageduration was 3.5 days, longer than trips in support of production. However, circuitryfactors were lower during drilling. The number of sites visited per trip ranged from oneto four, with an average of 1.25.

Activity AHTS Crew Fast supply Lift Supply Utility

Production 0 203 63 1 336 326Drilling 30 634 1,286 1 1,828 80Total 30 837 1,349 2 2,164 406Circuitry factor 2.39 1.22 2.10 1.29

Source: C-Logistics data

Table XVIII.Number of trips by boattype and activity andcircuitry factor duringproduction

Depth (feet) Productiona Drillinga

,200 2.9 4.7200 to 1,000 1.4 3.0.1,000 1.0 3.8Total 1.7 3.9

Notes: Values do not include circuitry, only the number of support visits conducted; asamplesize ¼ 24 sites for production; 33 sites for drillingSource: C-Logistics

Table XIX.Number of trips per weekduring production anddrilling by water depth inCL dataset

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7.3 LimitationsThe CL drilling data is almost exclusively deepwater drilling which may confounddrilling and production activity. The CL data was provided with flags describingwhether a voyage was related to drilling or production. Several sites were included asboth drilling and production. It is possible that both drilling and production occurredeither simultaneously or sequentially at these sites. It is also possible that somevoyages supported both drilling and production operations (due to circuitry) but werecoded as only supporting one or the other. Overall, this occurred in a small proportionof the total number of voyages and are not believed to bias the results significantly.

8. Interview and survey data8.1 Interview dataWe conducted phone interviews and electronic mail correspondence with managers of fiveOSV operations companies to serve as a check on the quantitative numbers discussedabove. The companies these managers worked for ranged from very large to very small.According to interviewees, drilling is the most intensive period of OSV use, especially overthe first several weeks a rig is on site. E&P companies usually have one crew boat and onesupply boat dedicated to each drilling operation. During drilling and for most shallowwater locations, supply boats make three trips per week, which is approximately themaximum number of trips a supply boat can make due to loading, unloading and traveltimes. For drilling projects farther offshore, operators may use two supply boats. Crewboats may make three to seven trips per week in support of drilling. Including both boattypes, drilling might require six to 13 trips per week. For manned platforms respondentsindicated that OSVs were needed two to three times per week.

8.2 Survey dataIn addition to conducting interviews with OSV operators, we also conducted surveys ofseveral independent E&P companies. We were provided summary estimates for thenumber of trips over the course of a year.

McMoRan. According to McMoRan’s, in 2008, they had 69 blocks in production intown areas. Vessels left from four shorebases: Intracoastal City, Fourchon, Freeport, andVenice. In general, a ship would make one trip per week to an area (for example, EugeneIsland) and visit all of the blocks in that area or other nearby areas. On average, each sitewould be visited 1.7 times per week during production and the circuitry factor was 6.9.Drilling was more OSV intensive. Only three sites were drilled in 2008. During drillingeach ship visited only one site before returning to port and on average visited seventimes per week.

Boat type Trips Percent of total Circuitry factor

AHTS 30 0.8 1.13Crew 634 16.4 1.21Fast supply 1,286 33.3 1.23Supply 1,828 47.4 1.29Utility 80 2.1 1.39Total 3,858 100.0 1.26

Source: C-Logistics data

Table XX.Distribution of trips byboat type and circuitryfactors during drilling

in CL dataset


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Stone energy. Stone energy provided data from 2007 to 2008. We used data from bothyears for construction and drilling data. Production data was identical in both years.The shorebases used were Dulac, Freshwater City, and Fourchon. Over two years, stonedrilled eight wells. The shorebase for seven of these eight wells was Fourchon, while thefinal well was sourced from Freshwater City. During drilling, there were 5.37 trips madeper week and OSVs never visited more than one site. A total of 43 blocks were included inproduction in 2008. Of these, all but one had only one site listed as a shorebase. One blockhad both Fourchon and Freshwater City listed as shorebases. During production,1.9 trips were made per week and the average circuitry was 3.33. During development,1.2 trips were made per week and the average circuitry was 2.4.

8.3 LimitationsThe interview and survey data is summary data and therefore less useful for developingaverage estimates of use by activity, however, it is useful as a check on the other datasources. Self reported data is often of highly variable quality, and for reasons describedpreviously cannot be used for modeling activity because of its coarse nature.

9. Comparisons among data sourcesComparisons of the various data sources are shown in Table XXI. The simple datapredicts that the average number of trips needed per week during drilling are between3.5 and 3.7 for crew boats and 3.2 for supply boats. The detailed data gives similarnumbers of 3.9 and 3.1 trips, respectively.

According to the simple data about 1.9 crew boats trips and 1.7 supply boat trips areneeded per week for construction. This assumes that the construction requires morevessel activity than production and that E&P companies report the maximum vesselusage in the simple data tables in the DOCD and EP plans. The comparable numbersfrom the detailed data are slightly larger, but generally agreeable. Using the averageconstruction times given in Table VII, the average number of crew boats needed per weekis 2.0 for caissons and 2.5 for platforms; the values for supply vessels are 2.2 and 2.1.

The simple and detailed data are not entirely independent and despite the largestandard deviations in the data they agree relatively well and the concordance providesa degree of confidence in the estimates.

There is general agreement between the Apache and plan data, especially in thetotal number of boats needed. The exception is in drilling in which the Apache datashows significantly greater OSV requirements. This discrepancy could occur if Apacheuses significantly more OSVs during drilling than average or if the actual number oftrips is different from the planned number of trips. Alternatively, this discrepancycould be due to the number of instances in which a single ship visited multiple drillingrigs in a single trip. In the Apache data, there were many instances in which OSVsvisited multiple drilling rigs during a single trip. In our analysis of Apache data, wecounted the number of times ships visited rigs rather than the number of trips. It ispossible that many DOCD and EP plans report only the number of trips, rather thanthe number of visits. In fact, based on discussions with industry participants, webelieve this is often the case.

The BP data contains trip numbers that are slightly lower than the other data fordrilling and slightly higher for production. This is likely due to the differences in waterdepth and distance to shore between the plan and Apache data and the BP data.

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Interview data generally matched the plan, Apache and BP data. The interview datasuggested a total of six to 13 trips per week in support of drilling. This matched theminimum and maximum averages obtained from the plan, BP and Apache data. Theinterview data suggested that during production manned platforms require manymore trips than unmanned platforms. This was not apparent in any other data source.

Despite large variances, the various data sources examined agree relatively well.Further, based on interviews with industry participants, the large variances appear tobe due to actual differences in OSV use patterns rather than statistical abnormalities;that is, the variances are functions of the large variances in the underlying data ratherthan under-sampling.

The critical issue with which there is limited agreement among data sources is theextent to which unmanned platforms are visited by OSVs during production. According tointerview data, unmanned platforms are treated differently from manned platforms andare visited less frequently during production; however, this was not apparent from theplan data as there were not large discrepancies between OSV needs for caissons (which aregenerally unmanned) and fixed platforms (which are more likely to be manned[9]). Giventhe large number of unmanned platforms and their relatively long lifetimes, theirtreatment in models of OSV use will be critical to overall OSV estimation.

No clear trend in circuitry factors emerged from the data. This was due to very largevariances in the data as well as our inability to compute circuitry factors from many of the

Activity Data source Crew boatsa Supply vessela Totala Circuit factor

Drilling Simple 3.5-3.7 3.2 6.7Detailed 3.1 3.9 7.0Apache 10.4 3.2 13.6 1.3BPb 2.4 1.7 4.36CLb 3.9 1.1-1.4Interview 6-13 1Stone 5.4McMoran 7

Production Simple 1.9 1.8 3.7Detailed 0.8 1.7 2.5BPb 2.4 2.4 5.8CL 1.7 1.2-2.4Interview 2-3 3.3-6.9Stone 1.7McMoran 1.9

P&A Apache 1.3 1.4 5.7 1BP 4.7

Construction Simple 1.9 1.7 3.6Detailed 2-2.5 2.1-2.2 4.1-4.7Apache 1.7 0.2 4.7 1.0Stone 1.2Interview 2.4

Pipeline Simple 2.5 2.4 4.9Detailed 0.9 2.2 3.1BP 2.5

Notes: aAll data are in trips per week; bindicates deepwater; blank values indicate estimate is notavailable

Table XXI.Comparison of data

sources for estimatingOSV needs


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available data types. Circuitry factors likely vary among companies more than usagerates as circuitry factors depend on the number of operations a company has ongoing ata time, their spatial distribution and supply needs. Furthermore, large E&P companiesoperating in deepwater may be comparatively uninterested in relatively small economiesgenerated by circuitry and are more likely to focus on ensuring that expensive deepwateroperations do not suffer downtime because an OSV is not available. In general, circuitryfactors between 1.2 and 2 appear typical for shelf operations.

10. ConclusionsThroughout the offshore basins of the world, wherever oil and gas is discovered, asupport industry will develop and evolve with the needs of industry and governmentregulation. In the US GOM, a large variety of marine vessels transport goods andprovide services to exploration, development and production activity. The spatial andtemporal dynamics of the logistics network is complex, dynamic and closelyinterrelated to the magnitude, duration, type and sequence of offshore workflows andactivities.

OSVs provide a vital link between offshore E&P activities and shore-basedfacilities. Offshore oil and gas operations cannot function without them, and theirutilization and spatial distribution provide a way of understanding the impacts ofthe oil and gas industry on coastal communities. The data presented here provide afirst attempt at quantifying the number of vessel trips required for offshore oil and gasdevelopment. The data can be used to partition OSV use among GOM shorebases, toallow for an estimation of total GOM-wide OSV use, for life-cycle analysis of offshoredevelopment, and a myriad of policy and planning applications both in the GOM and inoffshore basins generally.

OSVs have significant ecological impacts in terms of erosion (Bauer et al., 2002;Garel et al., 2008) and emissions (Wilson et al., 2007). The systematic study of the OSVindustry in either a single basin (as in this study) or a comparative context acrossbasins, could provide for efficiency gains in OSV utilization and consequent reductionsin emissions and wake effects. New technologies, most notably AIS, have recentlybecome available which may help in this effort (Perez et al., 2009).

This study, when combined with information on the geographic distribution of vesselactivity, provides the basic data for an estimation of shorebase specific OSV utilizationacross the US GOM, however, the methods and potentially some of the data, are applicableto other offshore basins as well. To determine the total OSV utilization in an offshore basin,one simply multiplies the utilization factor for a given stage provided in this paper by thenumber of facilities in that stage, divided by the circuitry factor, then sums across allstages. For example, if seven crew and supply vessels are needed per well drilled, and 100wells are drilled per year, a circuitry factor of 1.25 yields 165 trips per year ((7 £ 100)/1.25).

Notes

1. Offshore operations occur throughout the world on all continents except antartica. Mostoffshore reserves are located in deep water greater than 1,000 feet. At present, the principaldeepwater fields are located in the GOM, offshore Brazil, West Africa, Southeast Asia, andthe North Atlantic margin.

2. The OCS is the federally regulated waters of the GOM.

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3. For example, the seafloor terrain in the deepwater GOM is rougher than the relativelysmooth and gradually sloping seafloor of the shelf. Hills, valleys, and ridges with unstableand hard bottoms characterize deepwater topology.

4. Based on conversations with E&P company staff and consultants responsible for submittingthe plans, the number of visits by a boat to a site is generally the actual quantity input intothe DOCD plan.

5. For example, a DOCD plan might require one crew boat trip per week, but report only 26 inthe first year and 52 in the second year if the date of first production is expected to occurmidway through the first year.

6. A number of plans did not report information on production facilities; therefore, our totalsample size was 157, smaller than the data set presented in Table IX.

7. We tested the water depths associated with plans that did and did not contain vesselinformation using a two-tailed t-test and found a significant ( p ¼ 0.001) difference betweenthe minimum block water depth. This indicates that the data in our sample is biased towardsshallow water sites. We then conducted a regression analysis for which we had both vesselrequirements during production and minimum block water depths. No relationship betweenwater depth and vessel needs was found. Therefore, we believe our data are unlikely to bebadly biased due to the relative lack of deepwater plans.

8. For example, if a boat left port ten times and made 20 intra GOM movements, then theexpected number of visits made per embarkation would be (10 þ 20)/10) ¼ 3.

9. Of the 2,400 producing platforms in the GOM in 2008, about 900 were classified as manned24 hours.

References

Aas, B., Buvik, A. and Cakic, D. (2008), “Outsourcing of logistics activities in a complex supplychain: a case study from the Norwegian oil and gas industry”, International Journal ofProcurement Management, Vol. 1, pp. 280-96.

Aas, B., Halskau, O. and Wallace, S.W. (2009), “The role of supply vessels in offshore logistics”,Maritime Economics and Logistics, Vol. 11 No. 3, pp. 302-25.

Aas, B., Gribkovskaia, I., Halskau, O. Sr and Shlopak, A. (2007), “Routing of supply vessels topetroleum installations”, International Journal of Physical Distribution & LogisticsManagement, Vol. 37, pp. 164-79.

Ahmed, N. and Miller, H.J. (2007), “Time-space transformations of geographic space forexploring, analyzing, and visualizing transportation systems”, Journal of TransportGeography, Vol. 15, pp. 2-17.

Barrett, D. (2008), “The offshore supply boat sector”, Marine and Commerce, February, pp. 36-41.

Bauer, B.O., Lorang, M.S. and Sherman, D.J. (2002), “Estimating boat-wake-induced levee erosionusing sediment suspension measurements”, Journal of Waterway, Port, Coastal, andOcean Engineering, Vol. 128, p. 152.

Cairns, J.A. and Harris, H.A. (1988), “Firm location and differential barriers to entry in theoffshore oil supply industry”, Regional Studies, Vol. 22, pp. 499-506.

Fagerholt, K. and Lindstad, H. (2000), “Optimal policies for maintaining a supply service in theNorwegian Sea”, Omega, Vol. 28, pp. 269-75.

Finch, J.H. (2002), “Transferring exploration and production activities within the UK’s upstream oiland gas industry: a capabilities perspective”, Journal of Evolutionary Economics, Vol. 12,pp. 55-81.


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Fremont, A. (2007), “Global maritime networks: the case of Maersk”, Journal of TransportGeography, Vol. 15 No. 6, pp. 431-42.

Gale, B.G. and Albright, J. (1993), “Energy facility siting in coastal zones”, Coastal Zone’93:Proceedings of the Eighth Symposium on Coastal and Ocean Management, New Orleans,LA, USA, July 19-23, pp. 29-42.

Garel, E., Lopez Fernandez, L. and Collins, M. (2008), “Sediment resuspension events induced bythe wake wash of deep-draft vessels”, Geo-Marine Letters, Vol. 28, pp. 205-11.

Gerwick, B.C. (2007), Construction of Marine and Offshore Structures, 3rd ed., CRC Press,Boca Raton, FL, p. 813.

Gribkovskaia, I., Laporte, G. and Shlopak, A. (2007), “A tabu search heuristic for a routingproblem arising in servicing of offshore oil and gas platforms”, Journal of the OperationalResearch Society, Vol. 59, pp. 1449-59.

Holland, C.P., Shaw, D.R. and Kawalek, P. (2005), “BP’s multi-enterprise asset managementsystem”, Information and Software Technology, Vol. 47, pp. 999-1007.

Hull, B. (2002), “A structure for supply-chain information flows and its application to theAlaskan crude oil supply chain”, Logistics Information Management, Vol. 15, pp. 8-23.

Matos, S. and Hall, J. (2007), “Integrating sustainable development in the supply chain: the case oflife cycle assessment in oil and gas and agricultural biotechnology”, Journal of OperationsManagement, Vol. 25, pp. 1083-102.

MMS (2007), Proposed Final Program: Outer Continental Shelf Oil and Gas Leasing Program:2007-2012, US Department of the Interior, Minerals Management Service, Washington, DC.

Parola, F. and Veenstra, A.W. (2008), “The spatial coverage of shipping lines and containerterminal operators”, Journal of Transport Geography, Vol. 16 No. 4, pp. 292-9.

Perez, H.M., Chang, R., Billings, R. and Kosub, T.L. (2009), “Automatic identification systemsdata use in marine vessel emission estimation”, paper presented at the 18th InternationalAnnual Emissions Inventory Conference, Baltimore, MD, April 17-19.

Price, W. (1987), “Offshore oil and the coastal zone: a role for seaports”, Coastal Management,Vol. 15, pp. 229-45.

Randle, R.V. (1981), “Coastal energy siting dilemmas”, Natural Resources Journal, Vol. 21, p. 125.

Romero, M., Sheremetov, L. and Soriano, A. (2007), “A genetic algorithm for the pickup anddelivery problem: an application to the helicopter offshore transportation”, in Castillo, O.(Ed.,) Theoretical Advances and Applications of Fuzzy Logic and Soft Computing, Springer,Berlin.

Wilson, D., Billings, R., Oommen, R. and Chang, R. (2007), Year 2005 Gulfwide EmissionInventory Study, OCS Study MMS 2007-067, US Department of the Interior, MineralsManagement Service, Gulf of Mexico OCS Region, New Orleans, LA, p. 149.

Further reading

Antonsen, S. (2009), “The relationship between culture and safety on offshore supply vessels”,Safety Science, Vol. 47, p. 1118.

Bye, R. and Lamvik, G.M. (2007), “Professional culture and risk perception: coping with dangeron board small fishing boats and offshore service vessels”, Reliability Engineering &System Safety, Vol. 92, pp. 1756-63.

Jayawardana, J. and Hochstein, A. (2004), Supply Network for Deepwater Oil and GasDevelopment in the Gulf of Mexico: An Empirical Analysis of Demand for Port Services,OCS Study MMS 2004-047, Final Report: Prepared by UNO National Ports and Waterways

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Institute, US Department of the Interior, Minerals Management Service, Gulf of MexicoOCS Region, New Orleans, LA, p. 98.

Snow, N. (2009), “House members revive bill to expand OCS activity”, Oil & Gas Journal, Vol. 107No. 18.

Villasenor, R., Magdaleno, M., Quintanar, A., Gallardo, J.C., Lopez, M.T., Jurado, R., Miranda, A.,Aguilar, M., Melgarejo, L.A. and Palmeri’N, E. (2003), “An air quality emission inventoryof offshore operations for the exploration and production of petroleum by the Mexican oilindustry”, Atmospheric Environment, Vol. 37, pp. 3713-29.

Appendix. Minerals Management Service OSV activity estimationThe Outer Continental Shelf Lands Act (OCSLA) is the key statute governing US federal offshoreleasing and development. Enacted in 1953 and amended several times, the OCSLA (43 U.S.C 1331et seq.) is the Department of Interior’s primary authority for managing leasing activity on theOCS. The OCSLA codifies federal control of the OCS, and has as its primary purpose“expeditious and orderly development (of OCS resources), subject to environmental safeguards,in a manner which is consistent with the maintenance of competition and other national needs.”The MMS is the bureau within the Department of Interior that is responsible for developingleasing plans in consultation with coastal states and other stakeholders.

Section 1344 of the OCSLA requires the Department of Interior to maintain a five-year leasingprogram which reflects consideration of economic, social and environmental values, satisfies theNational Environmental Policy Act, and considers the inputs of federal agencies, the Governors ofaffected states, and programs developed under the Coastal Zone Management Act. In Section1346, the Department of Interior is directed to conduct environmental studies before and afterleasing to assess the impact of oil and gas development on the human, marine, and coastalenvironment of affected OCS and coastal areas. As part of the Environmental Impact Statements,the MMS estimates the number of service trips that arise from shore and their socioeconomicimpact.

The MMS describes offshore activities in the context of scenarios for the proposed actions andfor the OCS program (MMS, 2007). The OCS leasing program is two-tiered, involving five-yearprogram planning and individual lease sale planning and execution. Each scenario is a frameworkof assumptions based on estimated amounts, timing, and general locations of exploration,development, and production activities. Proposed actions are the individual lease sales and arerepresented by a range for resource estimates, projected exploration and development activities,and impact producing factors. Proposed sales are expected to lie within the scenario ranges, and aproposed action is considered representative of the individual proposed sales in each sale area.

A resource estimate is performed based upon the conditional estimates of undiscovered,unleased, conventionally recoverable oil and gas resources in the proposed lease sales areas, andestimates of the portion or percentage of these resources assumed to be leased, discovered,developed, and produced as a result of a proposed action. The projection of activities required tosupport the resource estimate is based on a combination of historical data, empirical relationshipsand correlations, published information, and expert opinion. MMS personnel estimate the amount ofactivity and apply duration and service vessel estimates to support the activity as shown in Table AI.A typical activity forecast is illustrated using the 2007-2012 Western Planning Area (WPA) leasesale (MMS, 2007). MMS personnel estimate that oil and gas production from the 2007-2012 WPAlease sale will result in a total of 0.242-0.423 billion barrels of oil and 1.644-2.647 trillion cubic feet ofgas. The total number of exploration and development wells to develop and produce these resourcesis estimated according to water depth (Table IV). Structure and pipeline installation, structureremovals and workovers are presented on a cumulative basis. Using the activity factors and relatedassumptions, the expected number of service vessel trips to support WPA development is estimatedto range between 94,000 and 155,000 cumulative marine vessel trips (Table AII).


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Corresponding authorBrian Snyder can be contacted at: [email protected]

Water depth (feet)

0-60 60-200 200-400 400-800 800-1,600 1,600-2,400 .2,400TotalWPA

Wells drilledExploration wells 23-36 5-7 1 3-4 5-10 2-3 3-5 42-66Development wells 64-89 13-15 6-7 9-13 48-75 9-15 6-8 155-221Oil wells 3-5 2-2 1-2 6-8 29-45 6-9 3-5 51-76Gas wells 61-84 10-13 5-5 3-5 20-30 3-6 2-3 105-146

Workovers andother well activities 392-539 77-91 35-42 56-77 294-455 56-91 35-49 945-1,344Production structures

Installed 21-31 2 1 1 1-3 1-2 1 28-41Removed 13-22 2 1 1 1-3 1 1 20-31

Pipelines installed (km) 60-420 NAa NA NA NA NA NA 130-760Service-vessel trips(1,000 round trips) 23-33 3 1 16-17 18-51 16-33 16-17 94-155Helicopter operations(1,000 operations) 300-680 30-44 14-22 14-22 14-66 14-44 14-22 400-900

Note: aNA ¼ not availableSource: Minerals Management Service

Table AII.Offshore scenarioinformation for the2007-2012 WPA proposedlease sale

Stage/activity Duration Vessel trips

DrillingExploration well 42 days 8 trips/weekDevelopment well 45 days 6 trips/week

ProductionStructure , 400 m 25 years 1 trip/10 daysStructure . 400 m 25 years 1 trip/1.75 days

Note: Sample activity factors employed in the 2007-2012 WPA proposed lease saleSource: Minerals Management ServiceTable AI.

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