well completion planning
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WELL COMPLETION PLANNING
ContentsContents Page Page
Introduction .................................................. 1Completion Planning Process ...................... 1
Reservoir Parameters .................................. 5Produced Fluid Characteristics .................... 6
Wellbore Construction.................................. 7Completion Assembly and Installation ......... 8Initiating Production ..................................... 9
Stimulation ................................................... 10
Well Service and Maintenance ....................11
Logistic, Location and Environment ............. 12Client Stock, Convention or Preference ....... 12
Regulatory Requirements ............................ 12Revenue and Cost ....................................... 13
Economic .....................................................13Company Objectives .................................... 13
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Although many wells (and fields) may be similar, the
success of each completion system should be closelybased on the individual requirements of each well. There-fore, generic design or installation procedures should be
carefully reviewed and amended as required.
The flow chart shown in Fig. 1 (principal phases summa-
rized in Fig. 3) reflects the general sequence in whichcompletion design and installation factors are typicallystudied. The "hook point" is provided as a reference pointto which specific procedures, detailed later in this manual,
will connect.
The economic impact of designing and installing non-optimized completions can be significant. Consequently
the importance of completing a thorough design andengineering process must be stressed. Delaying the com-mencement of the wells payout period is one example of
how non-optimized completion design, or performance,can effect the achievement of objectives. However, while
reducing installation cost and expediting start-up areimportant objectives, further reaching objectives, such as
long-term profitability must not be ignored (Fig. 2). As isillustrated, a more complex and costly completion mayprovide a greater return over a longer period. In addition,
the consequences of inappropriate design can have asignificant effect, e.g., requiring premature installation of
velocity string or artificial lift.
Introduction
Planning a completion, from concept through to installa-
tion, is a complex process comprising several distinctphases. Many factors must be considered, although in
most cases, a high proportion can be quickly resolved ordisregarded. Regardless of the complexity of the comple-
tion design, the basic requirements of any completionmust be kept in mind throughout this process, i.e., acompletion system must provide a means of oil or gas
production (or injection) which is safe, efficient and eco-nomic.
Ultimately, it is the predicted technical efficiency of a
completion system, viewed alongside the company objec-tives which will determine the configuration and compo-nents to be used.
Completion Planning Process
This section outlines the principal factors which should be
considered when planning an oil or gas well completion.
In addition to the technical influences on completiondesign and selection, economic and nontechnical issues
are also detailed. The relevance of these issues, incommon with technical details, is dependent on the cir-
cumstances pertaining to the specific well, completion orfield being studied.
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Component
Installation
Onsite
Preparation
Pre-installation Well Service Work Perform required treatments Drift run (minimum/essential)Surface/Production Equipment Preparation and checking
Budgetary Analyses Actual vs. plannedSafety and Environmental Factors
Precaution and contingency planning
Completion
Evaluation
Monitor Production Parameters Actual vs. ForecastEvaluate Production Response Actual vs. Forecast
Final Budgetary Analyses Actual vs. Forecast
Establish the objectives
and design basis
Essential Basics Safe Efficient EconomicLogistic and Location Surface and field facilities Location and wellsite constraints
Corporate Policy Medium and long-term objectives Contractual requirements/obligations
Determine the optimum
well performance
Reservoir Parameters Boundaries Structure Production mechanism Dimensions Rock Properties Rock compositionReservoir Fluid Characteristics Physical properties Chemical propertiesModelling and analyses NODAL analyses Perforation analyses Others
Budgetary Considerations Investment incentives Revenue(s) TaxationLegislative and Regulatory Safety and environmental factorsProduction Constraints Downstream capacity Flexibility of production Production profile Recoverability
Establish conceptualcompletion designs
Wellbore Construction Drilling phase considerations Evaluation phase considerations Pre-completion stimulationWorkover Philosophy Routine well service requirements Workover activitiesMaterial Selection Forces on completion components Wellbore environment constraintsReview Alternative Completions Compile list of alternatives/options Confirm preferred completion type
Budgetary Analyses Review outline completion costs
Starting
"philosophy
statement"
Finishing"philosophy
statement"
Cleanliness standards Completion components Completion fluidsDimensional checks Components String* Space-outEquipment handling Complex components Thread make-upProceedures Assembly installation Pressure testing Space-out)
Budgetary Analyses Actual vs. plannedSafety and Environmental Factors
Precaution and contingency planningRig time and well downtime Efficient completion
Fig. 1a. Phases of well completion planning and installation.
Flowchart Key
Technical requirementsconsiderations and issues
Non-technical andcommercial issues
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Procure components
and services
Issue Bid Request or Enquiry Technical specifications Scope of workBid Evaluation Design proposal Hardware selection Technical support
Associated services Innovative packaging (?)Recommendation Technical merit Integrated servicesVendors Meeting Confirm specifications/selection Review/revise the scope of workQuality Assurance/Control Inspection and verification Controls and checks
Issue Bid Request or Enquiry Contractual non-technical contentBid Evaluation (Commercial)
Price/cost Incentives/penalties Innovative packagingRecommendation AdministrativeVendors Meeting Establish contacts/form work group Issue formal orderQuality Assurance/Control Non-technical controls and checks
Planning of associated
service activities
Existing Completion Tubulars Partial or complete removal Preparation for concentric completionSelect Treatments Determined by specific conditionsPrepare Procedures Determined by application/conditions
Budgetary Analyses Return on Investment
Offsite
Preparation
Quality Assurance & Control Component Inspection Conformance to specified standardsPrepare Installation Procedure(s) Assembly Installation Testing Contingency PlansOffsite Assembly Check and test key components
Confirm Project Timing Lead times Operational windows
Quality Assurance & Control Delivery time compliance Quality documentation package/file
Review strategy for
well and field life
Production Strategy (Well/Field) Well performance Field performance Completion requirements
Local (Management) or Field Policy Medium- to long-term objectives Contractual requirementsImplications of Multiple Well Project Effect on cost Operational conflict Production conflict
Develop detailed
completion design
Specific Procedures
Velocity string
Gas lift installation
ESP installation
Completion Configuration Wellbore tubulars Wellbore and perforations Near wellbore matrix Hydraulic fracturingProduction Initiation Inducing flow Clean-up programCompletion Fluids Required density Chemical composition Additives Compatibility DisposalWell Service and Workover Completion function(s) Light service units (wireline & CT) Heavy service (snubbing and w/o rig)Surface Support Facilities Utilities Downstream facilitiesModelling and Analyses NODAL analyses OthersPerforating SPAN* analyses Charge and gun selection
Client Convention and Preference Existing stock Contractual obligations Corporate or local policies Familiarity and acceptanceDetailed Budget Capital cost Installation cost Operating cost Maintenance cost (routine) Major servicing cost (periodic)Establish Project Time Scale Component availability Lead time(s) Operational windows Simultaneous operations (offshore)
HOO
KPO
INTFOR S
PECIFICPROCEDU
RES
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ESTABLISH THE OBJECTIVES
AND DESIGN BASIS
DETERMINE THE OPTIMUM
WELL PERFORMANCE
ESTABLISH CONCEPTUALCOMPLETION DESIGNS
REVIEW STRATEGY FOR LIFEOF THE WELL AND FIELD
DEVELOP DETAILEDCOMPLETION DESIGN
PROCUREMENT OF
COMPONENTS AND SERVICES
PLANNING OF ASSOCIATED
WELL SERVICE ACTIVITIES
OFFSITE PREPARATION
ONSITE PREPARATION
INSTALLATION
EVALUATION
Fig. 2. Consequences of a non-optimized completion system.
Fig. 3. Principal phases of well completion.
Drilling, DST, completion
logging and stimulation
Optimized
productionNon-optimized
production
Time (Life of the well)
Expenditure/Revenue
+$
-$
EnhancedRecovery
Stimulation
Thru-tubing
W/O
Profile
Modification
P & A
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Reservoir Boundaries
Structural trapsStaratographic traps
UnconformitiesPermeability contrasts
Reservoir Structure
Continuity
Permeability barriersIsotropy
RESERVOIR PARAMETERS
Production Mechanism
Water drive
Solution gasGas cap
CombinationInjectionArtificial
Physical Parameters
SizeShape
HeightPressure
Temperature
Rock Properties
PorosityPermeability
Pore size distribution
Fluid saturationGrain size and shape
Wettability
Rock Composition
CompositionConsolidationContaminationClay content
Moveable finesCementaceous material
Scale forming materials
Fig. 4. Reservoir parameters.
Reservoir Parameters
The type of data outlined in this category are obtained byformation and reservoir evaluation programs such as
coring, testing and logging. Typically, such data will beintegrated by reservoir engineers to compose a reservoir
model.
The reservoir structure, continuity and production drive
mechanism are fundamental to the production process ofany well. Frequently, assumptions are made of these
factors which later prove to be significant constraints onthe performance of the completion system selected.
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Physical Properties
Oil densityGas gravity
ViscosityPour point
Gas-oil ratio
Water-oil ratio
Chemical Properties
Composition
Wax contentAsphaltenes
Corrosive agentsToxic components
Scale
PRODUCED FLUID CHARACTERISTICS
Fig. 5. Produced fluid characteristics.
Physical characteristics of the reservoir are generally
more easily measured or assessed. Pressure and tem-perature are the two parameters most frequently used in
describing reservoir and downhole conditions. The effectsof temperature and pressure on many other factors can besignificant. For example, corrosion rates, selection of
elastomer or seal materials and the properties of pro-duced fluids are all effected by changing temperature and
pressure.
When investigating the reservoir rock characteristics, the
principal concern is assessing formation behavior andreaction. This includes behavior and reaction to the drill-
ing, production or stimulation treatments which may berequired to fully exploit the potential of the reservoir.
The formation structure and stability should be closely
investigated to determine any requirement for stimulationor sand control treatment as part of the completion pro-cess.
The reservoir characteristics effecting completion con-
figuration or component selection are best summarizedby reviewing the reservoir structure, continuity, drive
mechanism and physical characteristics. These shouldbe reviewed alongside the physical and chemical proper-ties of the formation (Fig. 4).
Produced Fluid Characteristics
Two conditions, relating to the chemical properties of the
produced fluid most effect the physical qualities of comple-
tion components and materials. These are chemical depo-
sition (scale, asphaltenes etc.) and chemical corrosion(weight loss and material degradation). Both conditions
still account for significant losses in production and deg-radation of equipment in many fields.
The ability of the reservoir fluid to flow through the comple-tion tubulars and equipment, including the wellhead and
surface production facilities, must be assessed. For ex-ample, as the temperature and pressure of the fluid
changes, the viscosity may rise or wax may be deposited.
Both conditions may place unacceptable back-pressure,thereby dramatically reducing the efficiency of the comple-
tion system.
While the downhole conditions contributing to these fac-tors may occur over the lifetime of the well, consideration
must be made at the time the completion components arebeing selected. Cost effective completion designs gener-ally utilize the minimum acceptable components of an
appropriate material. In many cases, reservoir anddownhole conditions will change during the period of
production. The resulting possibility of rendering thecompletion design or material unsuitable should be con-
sidered during the selection process.
The production fluid characteristics effecting completion
configuration or component selection are best summa-rized by reviewing the physical and chemical properties of
the fluid (Fig. 5).
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Wellbore Construction
Wellbore construction factors can be categorized in the
following phases.
Drilling The processes required to efficiently drill to,and through the reservoir.
Coring and testing The acquisition of wellbore survey
and reservoir test data used to identify completiondesign constraints.
Pre-completion stimulation or treatment Final prepa-ration of the wellbore through the zone of interest for the
completion installation phase.
It is an obvious requirement that the drilling program mustbe designed and completed within the scope and limitsdetermined by the completion design criteria.
Most obvious are the dimensional requirements deter-
mined by the selected completion tubulars and compo-nents. For example, if a multiple string completion is to be
selected, an adequate size of production casing (andconsequently hole size) must be installed. Similarly, thewellbore deviation or profile can have a significant impact.
Drilling and associated operations, e.g., cementing, per-formed in the pay zone must be completed with extra
vigilance. It is becoming increasingly accepted that the
prevention of formation damage is easier, and much morecost effective, than the cure. Fluids used to drill, cement or
service the pay zone should be closely scrutinized andselected to minimize the likelihood of formation damage.
Similarly, the acquisition of accurate data relating to the
pay zone is important. The basis of several major deci-sions concerning the technical feasibility and economicviability of possible completion systems will rest on the
data obtained at this time.
A pre-completion stimulation treatment is frequently con-ducted. This is often part of the evaluation process in a
test-treat-test program in which the response of the reser-voir formation to a stimulation treatment can be assessed.
The wellbore characteristics affecting completion con-figuration or component selection are best summarized
by reviewing the drilling, evaluation and pre-completionactivities (Fig. 6).
Fig. 6. Wellbore construction
Drilling
Hole size
DepthDeviation
Well path
Formation damage
Pre-completion
Casing schedules
Primary cementingPre-completion stimulation
WELLBORE CONSTRUCTION
Evaluation
LoggingCoring
TestingFluid sampling
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Completion Assembly and Installation
This stages marks the beginning of what is commonly
perceived as the completion program. It is the intent ofthis manual to enlighten readers as to the true and
necessary extent of the completion program. As hasbeen demonstrated, considerable preparation, evalua-
tion and design work has been completed before thecompletion tubulars and components are selected.
With all design data gathered and verified, the completioncomponent selection, assembly and installation process
commences. This phase carries obvious importance sincethe overall efficiency of the completion system depends
on proper selection and installation of components.
A visionary approach is necessary since the influence ofall factors must be considered at this stage, i.e., factorsresulting from previous operations or events, plus an
allowance, or contingency, for factors which are likely orliable to effect the completion system performance in the
future.
The correct assembly and installation of components inthe wellbore is as critical as the selection process by whichthey are chosen.
This is typically a time at which many people and re-sources are brought together to perform the operation.
Consequently, the demands brought by high, and mount-
ing daily charges imposes a sense of urgency whichrequires the operation be completed without delay.
To ensure the operation proceeds as planned, it is essen-
tial that detailed procedures are prepared for each stageof the completion assembly and installation. The com-
plexity and detail of the procedure is largely dependent onthe complexity of the completion.
In general, completion components are broadly catego-rized as follows.
Primary completion components
Ancillary completion components
Primary completion components are considered essen-tial for the completion to function safely as designed. Such
components include the wellhead, tubing string, safetyvalves and packers. In special applications, e.g., artificial
lift, the components necessary to enable the completionsystem to function as designed will normally be consid-ered primary components.
Fig. 7. Completion assembly and installation.
Primary Components
Wellhead
Xmas treeTubing
Packer
Safety valve
Ancillary Components
Circulating devices
NipplesFlow couplings
Injection mandrels
Tubing seal assembly
COMPLETION ASSEMBLY AND INSTALLATION
Completion Fluids
Completion fluidPacker fluid
Perforating fluidKick-off fluid
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Ancillary completion components enable a higher level ofcontrol or flexibility for the completion system. For ex-
ample, the installation of nipples and flow control devices
can allow improved control.
Several types of device, with varying degrees of impor-tance, can be installed to permit greater flexibility of the
completion. While this is generally viewed as beneficial, acomplex completion will often be more vulnerable to
problems or failure, e.g., due to leakage.
The desire for flexibility in a completion system stems from
the changing conditions over the lifetime of a well, field orreservoir. For example, as the reservoir pressure de-
pletes, gas injection via a side-pocket mandrel may benecessary to maintain optimized production levels.
A significant fluid sales and service industry has evolvedaround the provision of completion fluids. Completion
fluids often require special mixing and handling proce-dures, since (i) the level quality control exercised on
density and cleanliness is high, and (ii) completion fluidsare often formulated with dangerous brines and inhibitors.
The ultimate selection of completion components andfluids should generally be made to provide a balance
between flexibility and simplicity.
The completion component selection factors are bestsummarized by reviewing the primary and ancillary com-
ponents, and installation procedures (Fig. 7).
Initiating Production
The three stages associated with this phase of the comple-
tion process include (Fig. 8 and 9).
Kick-off
Clean up
Stimulation
The process of initiating flow and establishing communi-
cation between the reservoir and the wellbore is obviouslyclosely associated with perforating operations. If the well
is to be perforated overbalanced, then the flow initiationand clean up program may be dealt with in separate
procedures. However, if the well is perforated in anunderbalanced condition, the flow initiation and clean upprocedures must commence immediately upon perfora-
tion.
The benefits of underbalanced perforating are well docu-mented and the procedure is now conducted on a routine
basis. While the reservoir/wellbore pressure differentialmay be sufficient to provide an underbalance at time ofperforation, the reservoir pressure may be insufficient to
cause the well to flow after the pressure has equalized.
Adequate reservoir pressure must exist to displace thefluids from within the production tubing if the well is to flow
unaided. Should the reservoir pressure be insufficient toachieve this, measures must be taken to lighten the fluid
Clean-up Program
Initial flowrate andrate of increase
Evaluation program
Testtreattest
PRODUCTION INITIATION
Inducing Flow
Gas liftNitrogen kick-off
Light-fluid circulationUsing completion components
or coiled tubing
Fig. 8. Production initiation.
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Near Wellbore and Reservoir Matrix
Matrix acidizing
Hydraulic fracturingNon-acid treatments
STIMULATION
Wellbore and Perforations
Wellbore clean-upPerforating acid
Perforation wash
Fig. 9. Stimulation
column - typically by gas lifting or circulating less dense
fluid. The preparations for these eventualities are part ofthe completion design process.
The flowrates and pressures used to exercise controlduring the clean up period are intended to maximize the
return of drilling or completion fluids and debris. Thiscontrolled backflush of perforating debris or filtrate also
enables surface production facilities to reach stable con-ditions gradually.
In some completion designs, an initial stimulation treat-ment may be conducted at this stage. An acid wash or
soak placed over the perforations has proved effective in
some conditions. However, as underbalanced perforatingbecomes more popular, the need and opportunity for thistype of treatment has diminished.
Stimulation
There are four general categories of stimulation treatmentwhich may be considered necessary during the process of
completing a well.
Wellbore cleanup
Perforation washing or opening
Matrix treatment of the near wellbore area
Hydraulic fracturing
Wellbore clean up will not normally be required with newcompletions. However, in wells which are to be reperforated
or in which a new pay zone is to be opened, a well bore
clean up treatment may be appropriate. There are a range
of perforation treatments which may be associated withnew or recompletion operations.
Perforating acids and treatment fluids are designed to be
placed across the interval to be perforated before the gunsare fired. Used in overbalanced perforating applications,
the perforating acid or fluid reduces the damage resultingfrom the perforating operation. Perforation washing is anattempt to ensure that as many perforations as possible
are contributing to the flow from the reservoir. Rockcompaction, mud and cement filtrate and perforation
debris have been identified as types of damage which willlimit the flow capacity of a perforation, and therefore
completion efficiency.
If the objective of the treatment is to remove damage in or
around the perforation, simply soaking acid across theinterval is unlikely to be adequate. The treatment fluid
must penetrate and flow through the perforation to beeffective. In which case all the precautions associated
with a matrix treatment must be exercised to avoid caus-ing further damage by inappropriate fluid selection.
Matrix treatment of the near wellbore area may be de-signed to remove or by-pass the damage. Hydraulic
fracturing treatments provide a high conductivity channel
through any damaged area and extending into the reser-voir.
Both matrix and hydraulic fracturing treatments require adetailed design process which is documented in therelevant Stimulation Manual.
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Well Service and Maintenance Requirements
The term well servicing is used (and misused) to de-scribe a wide range of activities including :
Routine monitoring
Wellhead and flowline servicing
Minor workovers (thru-tubing)
Major workovers (tubing pulled)
Emergency response and containment
Well service or maintenance preferences and require-
ments must be considered during the completion designprocess. With more complex completion systems, the
availability and response of service and support systemsmust also be considered (Fig.10).
Wellbore geometry and completion dimensions deter-
mine the limitations of conventional slickline, wireline,coiled tubing or snubbing services in any application.
WELL SERVICE AND WORKOVER
Fig. 10. Well service and workover.
Completion System Function
Well testing androutine monitoring
Emergency kill and containment
Heavy Workover Units
Drilling rig
Workover rigCombined CT and
snubbing unit
Light Service Units
Slickline
Electric wireline
Coiled tubingSnubbing
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Location
Access to well
Weather/climatic conditionsEnvironmental constraints
Proximity of neighboring interests
LOGISTIC AND LOCATION CRITERIA
Surface Facilities
Separator capacityExport capability
Operational flexibilityDisposal facility
Logistic, Location and Environmental Constraints
Restraints imposed by logistic or location driven criteriaoften compromise the basic cost effective requirement
of a completion system. Special safety and contingencyprecautions or facilities are associated with certain loca-tions, e.g., offshore and subsea.
A summary of the logistic, location and environmental
constraints affecting completion design and configurationinclude well location, environmental conditions, weather
conditions and adjacent land use (Fig 11).
Client Stock, Convention or Preference
The completion configuration and design must ultimately
meet all requirements of the client. In many cases, theserequirements may not be directly related to the reservoir,
well or location (technical factors). An awareness of thesefactors, and their interaction with other completion designfactors can help save time and effort in an expensive
design process.
The following factors are common criteria which must be
considered.
Existing material stocks or contractual obligation
Compatibility with existing downhole or wellhead compo-nents
Fig. 11 Logistic and location criteria
Client familiarity and acceptance
Reliability and consequences of failure
Regulatory Requirements
There are several regulatory and safety requirements
applicable to well completion operations. These mustgenerally be fully satisfied during both the design and
execution phases of the completion process.
Provision for well-pressure and fluid barriers
Safety and operational standards
Specifications, guidelines and recommendations
Disposal requirements
Emergency and contingency provisions
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Revenue and Costs
When completing an economic viability study, or compari-
son, the costs associated with each of the followingcategories should normally be investigated.
Production revenue
Capital cost (including completion component and instal-
lation cost)
Operating cost (including utilities and routine mainte-nance or servicing cost, also workover, replacement or
removal cost.
The specific conditions, determined by the completion
being studied, can be applied to enable a complete andrepresentative cost analysis. In most cases, the order of
importance is as shown, with the revenue stream beingmost critical.
Installation costs are significant if special completionrequirements impact the overall drilling or completion
time. The actual cost of completion components is oftenrelatively insignificant when viewed alongside the value of
incremental production from improved potential or in-creased uptime.
Economic
The economic factors shown below are beyond the scopeof technical preparation for well completion design. How-
ever, they undoubtedly influence the industry. Conse-quently a rudimentary understanding of the factors, and
their interaction with factors previously discussed is ben-eficial.
Market forces (including seasonal fluctuations and swingproduction)
Taxation (including tax liability or breaks)
Investment availability
Company Objectives
A measure of success can only be effectively made if there
are clearly stated objectives. Such objectives may bemacroscopic, but nonetheless will influence the specificobjectives as applied to an individual well or completion.
In addition, the wider company objectives may allowclarification of other selection factors, e.g., where two ormore options offer similar or equal benefit, and no clear
selection can be made on a technical basis.
Desired payback period
Cash flow
Recoverable reserves