Subsea Engineering Handbook

908 Pages·2012·42.673 MB·English

by  Yong Bai and Qiang Bai (Eds.)

11
CHAPTER
Overview of Subsea Engineering
Contents
1.1. Introduction 3
1.2. SubseaProductionSystems 6
1.2.1.FieldArchitecture 7
1.2.2.DistributionSystems 9
1.2.3.SubseaSurveys 10
1.2.4.InstallationandVessels 11
1.2.5.CostEstimation 11
1.2.6.SubseaControl 12
1.2.7.SubseaPowerSupply 12
1.2.8.ProjectExecutionandInterfaces 13
1.3. FlowAssuranceandSystemEngineering 13
1.3.1.SubseaOperations 13
1.3.2.CommissioningandStart-Up 15
1.3.3.ProductionProcessing 16
1.3.4.ChemicalsInjection 16
1.3.4.1. HydrateInhibition 16
1.3.4.2. ParaffinInhibitors 17
1.3.4.3. AsphalteneInhibitors 17
1.3.5.WellTesting 17
1.3.6.InspectionandMaintenance 18
1.4. SubseaStructuresandEquipment 18
1.4.1.SubseaManifolds 18
1.4.2.PipelineEndsandIn-lineStructures 19
1.4.3.Jumpers 19
1.4.4.SubseaWellheads 20
1.4.5.SubseaTrees 22
1.4.6.UmbilicalSystems 22
1.4.7.ProductionRisers 24
1.5. SubseaPipelines 24
References 25
1.1. INTRODUCTION
The world’s energy consumption has increased steadily since the 1950s. As
showninFigure1-1,thefossilfuels(oil,naturalgas,andcoal)stillamountto
80%oftheworld’senergyconsumptioneventhoughaconsiderablenumber
of initiatives and inventions in the area of renewable energy resources have
SubseaEngineeringHandbook (cid:1)2012ElsevierInc. j
ISBN978-0-12-397804-2,doi:10.1016/B978-0-12-397804-2.00001-1 Allrightsreserved. 3
4 Y.BaiandQ.Bai
Figure 1-1 Coal,Oil,andNaturalGasConsumption[1]
decreasedtheiruse.Therapidrisesincrudeoilpricesduringthelate2000s
is a response to increasing demand for oil and gas. Of the fossil fuels
consumed,almost 80% areoil and gas;therefore,the production of oil and
gas is of major importance to the stabilityof the world’s energy supply.
The offshore oil and gas industry started in 1947 when Kerr-McGee
completedthefirstsuccessfuloffshorewellintheGulfofMexico(GoM)off
Louisiana in 15 ft (4.6 m) of water [2]. The concept of subsea field
development was suggested in the early 1970s by placing wellhead and
production equipment on the seabed with some or all components
encapsulated in a sealed chamber [3]. The hydrocarbon produced would
thenflowfromthewelltoanearbyprocessingfacility,eitheronlandoron
an existing offshore platform. This concept was the start of subsea engi-
neering, and systems that have a well and associated equipment below the
water surface are referred as subsea production systems. Figure 1-2 shows the
number of shallow and deepwater subsea completions in the GoM from
1955to2005.Subseacompletionsinlessthan1,000ft(305m)waterdepths
are considered to be shallow-water completions, whereas those at depths
greater than 1,000 ft (305 m) areconsidered to be deepwatercompletions.
In the past 40 years, subsea systems have advanced from shallow-water,
manually operated systems into systems capable of operating via remote
control at water depths of up to 3,000 meters (10,000 ft).
With the depletion of onshore and offshore shallow-water reserves, the
exploration and production of oil in deepwaterhas become achallenge to
OverviewofSubseaEngineering 5
Figure 1-2 Number of Shallow and Deepwater Subsea Completions Each Year from
1955to2005[4]
theoffshoreindustry.Offshoreexplorationandproductionofoilandgasare
advancing into deeper waters at an increasing pace. Figure 1-3 shows the
maximum water depth of subsea completions installed each year in the
GoM.Figure1-4illustratesoffshoreoilproductiontrendsintheGoMfrom
shallow and deep water. Offshore oil production from deep water has
Figure 1-3 Maximum Water Depth of Subsea Completions Installed Each Year from
1955to2005[4]
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Figure 1-4 OffshoreOilProductioninGoM[5]
increasedsharplysince1995,startingatapproximately20millionbarrelsof
oil equivalent (MMBOE) per year from deep water.
The subsea technology used for offshore oil and gas production is
a highly specialized field of application that places particular demands on
engineering. The subsea production system carries some unique aspects
relatedtotheinaccessibilityoftheinstallationanditsoperationandservicing.
These special aspects make subsea production a specific engineering disci-
pline. This book will discuss the topics of subsea engineering in four parts:
Part 1: Subsea Production Systems
Part 2: Flow Assurance and System Engineering
Part 3: Subsea Structures and Equipment
Part 4: Subsea Umbilicals, Risers, and Pipelines.
1.2. SUBSEA PRODUCTION SYSTEMS
A subsea production system consists of a subsea completed well, seabed
wellhead, subsea production tree, subsea tie-in to flowline system, and
subsea equipment and control facilities to operate the well. It can range in
complexity from a single satellite well with a flowline linked to a fixed
platform,FPSO(FloatingProduction,StorageandOffloading),oronshore
facilities, to several wells on a template or clustered around a manifold that
transfer to a fixed or floating facilityor directly to onshore facilities.
As the oil and gas fields move further offshore into deeper water and
deeper geological formations in the quest for reserves, the technology of
drillingandproductionhasadvanceddramatically.Conventionaltechniques
OverviewofSubseaEngineering 7
Figure1-5 AllSegmentsofaSubseaProductionSystem[6]
restrict the reservoir characteristics and reserves that can be economically
exploited in the deep waters now being explored. The latest subsea tech-
nologieshavebeenprovenandformedintoanengineeringsystem,namely,
the subsea production system, which is associated with the overall process
and all the equipment involved in drilling, field development, and field
operation,asshowninFigure1-5.Thesubseaproductionsystemconsistsof
the following components:
(cid:129) Subsea drilling systems;
(cid:129) Subsea Christmas trees and wellhead systems;
(cid:129) Umbilical and riser systems;
(cid:129) Subsea manifolds and jumper systems;
(cid:129) Tie-in and flowline systems;
(cid:129) Control systems;
(cid:129) Subsea installation.
Figure1-6illustratesthedetailedrelationshipamongthemajorcomponents
of a subsea production system.
Most components of the subsea production system will be described in
thechaptersinPart1,whilethecomponentsofsubseastructuresandsubsea
equipment will be the focus of other parts of this book.
1.2.1. Field Architecture
Subsea production systems are generally arranged as shown in Figure 1-7.
Some subsea production systemsareused to extend existing platforms.For
example, the geometry and depth of a reservoir may be such that a small
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Figure1-6 RelationshipamongtheMajorComponentsofaSubseaProductionSystem
Figure1-7 TypicalSubseaProductionSystemwithWetTree[7]
OverviewofSubseaEngineering 9
section cannot be reached easily from the platform using conventional
directional drilling techniques or horizontal wells. Based on the location
of the tree installation, a subsea system can be categorized as a dry tree
production system or a wet tree production system. Water depth can also
impactsubseafielddevelopment.Fortheshallowerwaterdepths,limitations
on subsea development can result from the height of the subsea structures.
Christmas trees and other structures cannot be installed in water depths of
less than 30 m (100 ft). For subsea development in water depths less than
30 m (100 ft), jacket platforms consisting of dry trees can be used.
The goal of subsea field development is to safely maximize economic
gainusingthemostreliable,safe,andcost-effectivesolutionavailableatthe
time. Even though wet well systems are still relatively expensive, their
attraction in reducing overall capital expenditures has already been made
clear.Subseatie-backsarebecomingpopularinthedevelopmentofnewoil
and gas reserves in the 21st century. With larger oil and gas discoveries
becoming less common, attention has turned to previously untapped, less
economically viable discoveries.
In subsea field development, the following issues should be considered:
(cid:129) Deepwater or shallow-water development;
(cid:129) Dry tree or wet tree;
(cid:129) Stand alone or tie-back development;
(cid:129) Hydraulic and chemical units;
(cid:129) Subsea processing;
(cid:129) Artificial lift methods;
(cid:129) Facility configurations (i.e., template, well cluster, satellite wells,
manifolds).
The advantages, disadvantages, and limitations of the above issues will be
described in the relevant sections of Chapter 2, which covers field
architecture.
1.2.2. Distribution Systems
The subsea system is associated with the overall process and all equipment
involved in the arrangement. It is designed in such a way that safety, envi-
ronment protection, and flow assurance and reliability are taken into
consideration for all subsea oil and gas exploitation. Subsea distribution
systemsconsistofagroupofproductsthatprovidecommunicationbetween
subsea controls and topside controls for all equipment via an umbilical
system.
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Subsea distribution systems may include, but not be limited to, the
following major components [8]:
(cid:129) Topside umbilical termination assembly (TUTA);
(cid:129) Subsea accumulator module (SAM);
(cid:129) Subsea umbilical termination assembly (SUTA), which includes:
(cid:129) Umbilical termination head (UTH);
(cid:129) Hydraulic distribution manifold/module (HDM);
(cid:129) Electric distribution manifold/module (EDM);
(cid:129) Flying leads.
(cid:129) Subsea distribution assembly (SDA);
(cid:129) Hydraulic flying leads (HFLs);
(cid:129) Electric flying leads (EFLs);
(cid:129) Multiple quick connector (MQC);
(cid:129) Hydraulic coupler;
(cid:129) Electrical connector;
(cid:129) Logic caps.
The advantages, disadvantages, and limitations of the above components
will be described in the relevant sections of the chapter on subsea
distribution systems, Chapter 3.
1.2.3. Subsea Surveys
The subsea survey for positioning and soil investigation is one of the main
activities for subsea field development. As part of the planned field devel-
opment, a detailed geophysical and geotechnical field development survey
togetherwithsoilinvestigationisperformed.Thepurposeofthesurveyisto
identify the potential man-made hazards, natural hazards, and engineering
constraints of a proposed subsea field area and pipeline construction; to
assessthepotentialimpactonbiologicalcommunities;andtodeterminethe
seabed and sub-bottom conditions. In Chapter 4, the following issues
related to subsea surveys are discussed:
(cid:129) Establishing vertical route profiles, a contour plan, and the seabed’s
features, particularly any rock outcrops or reefs;
(cid:129) Obtaining accurate bathymetry, locating all obstructions, and identi-
fying other seabed factors that may affect the development of the
selected subsea field area including laying, spanning, and stabilityof the
pipeline;
(cid:129) Carrying out a geophysical surveyof the selectedsubsea field androute
to define the shallow sub-seabed geology;
OverviewofSubseaEngineering 11
(cid:129) Carrying out geotechnical sampling and laboratory testing in order to
evaluate precisely the nature and mechanical properties of soils at the
selected subsea field area and along the onshore and offshore pipelines
and platform locations;
(cid:129) Locating existing subsea equipment (e.g., manifold, jumper, and subsea
tree), pipelines, and cables, both operational and redundant, within the
survey corridor;
(cid:129) Determiningthetypeofsubseafoundationdesignthatisnormallyused
for subsea field development.
1.2.4. Installation and Vessels
The development of subsea production systems requires specialized subsea
equipment. The deployment of such equipment requires specialized and
expensive vessels, which need to be equipped with diving equipment for
relativelyshallowequipmentwork,androboticequipmentfordeeperwater
depths.Subseainstallationreferstotheinstallationofsubseaequipmentand
structures in an offshore environment for the subsea production system.
Installation in an offshore environment is a dangerous activity, and heavy
lifting is avoided as much as possible. This is achieved fully by subsea
equipment and structures that are transmitted to the installation site by
installationvessels.
Subsea installation can be divided into two parts: installation of subsea
equipmentandinstallationofsubseapipelinesandsubsearisers.Installation
of subsea equipment such as trees and templates can be done bya conven-
tional floating drilling rig, whereas subsea pipelines and subsea risers are
installedbyaninstallationbargeusingS-lay,J-lay,or reellay.Theobjective
of Chapter 5 is to reviewexisting vessels used for the installation of subsea
equipmentsuchastrees,manifolds,flowlines,andumbilicals.Thisincludes
special vessels that can run the trees and rigless installation. Subsea equip-
ment to be installed is categorized based on weight, shapes (volume versus
line type), dimensions, and water depth (deep versus shallow).
1.2.5. Cost Estimation
When considering a subsea system as a development option for a specific
reservoirandnumberofwellsrequired,thesubseacostisrelativelyflatwith
increasingwaterdepth.For therigidplatformcase,however,costsincrease
rapidlywithwaterdepth.Therefore,deeperwater tendstofavor theuseof
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subsea systems. Conversely, for a given water depth and location, platform
costs are less sensitive to an increasing number of wells; well drilling from
a platform is relatively inexpensive, and the platform structure cost is gov-
erned more by water depth, process requirements, and environment. The
use of mobile drilling units for subsea wells increases drilling costs.
Therefore, situations where a relatively small number of wells are needed
favor the use of a subsea system.
Subsea costs refer to the cost of the whole subsea project and generally
include capital expenditures (CAPEX) and operating expenditures
(OPEX). CAPEX is the total amount of investment necessary to put
aprojectintooperationandincludesthecostofinitialdesign,engineering,
construction, and installation. OPEX is the expenses incurred during the
normaloperationofafacility,orcomponentaftertheinstallation,including
labor, material, utilities, and other related expenses. OPEX contains
operational costs, maintenance costs, testing costs, and other related costs.
Chapter 6 covers cost estimates in detail.
1.2.6. Subsea Control
The subsea production control system is defined as the control system
operating a subsea production system during production operations
according to ISO 13628-6 [9]. The subsea control system is the heart of
anysubseaproductionsystem,anditisarelativelylow-costitemcompared
tothecostofdrilling,linepipe,installation,etc.Therefore,controlsystems
are usually low on the list of initial project priorities. However, ignoring
the complexity, the number of components and interfaces can lead to
problems with installation and commissioning and to long-term reliability
issues.
In the chapter on subsea control, Chapter 7, the principles and char-
acteristics of subsea production control systems are explained and the
advantages, disadvantages, and limitations are compared. The government
regulations, industry codes, recommended practices, and environmental
specifications that apply to subsea control systems are detailed.
1.2.7. Subsea Power Supply
Powersupplyisakeyfactorinsubseaprocessing.Thesubseapowersupplyis
an important component in the systems necessary for processing the well
streamattheseabedclosetothewells.Nothavingthepowersupplysystem
in place can stop the development of subsea processing.