well completion planning

WELL COMPLETION PLANNING Page

Contents

Introduction .................................................. 1 Completion Planning Process ...................... 1 Reservoir Parameters .................................. 5 Produced Fluid Characteristics .................... 6 Wellbore Construction .................................. 7 Completion Assembly and Installation ......... 8 Initiating Production ..................................... 9 Stimulation ................................................... 10

Contents

Page

Well Service and Maintenance .................... 11 Logistic, Location and Environment ............. 12 Client Stock, Convention or Preference ....... 12 Regulatory Requirements ............................ 12 Revenue and Cost ....................................... 13 Economic ..................................................... 13 Company Objectives .................................... 13

Introduction Planning a completion, from concept through to installation, is a complex process comprising several distinct phases. Many factors must be considered, although in most cases, a high proportion can be quickly resolved or disregarded. Regardless of the complexity of the completion design, the basic requirements of any completion must be kept in mind throughout this process, i.e., a completion system must provide a means of oil or gas production (or injection) which is safe, efficient and economic. Ultimately, it is the predicted technical efficiency of a completion system, viewed alongside the company objectives which will determine the configuration and components 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 completion design and selection, economic and nontechnical issues are also detailed. The relevance of these issues, in common with technical details, is dependent on the circumstances pertaining to the specific well, completion or field being studied.

Although many wells (and fields) may be similar, the success of each completion system should be closely based on the individual requirements of each well. Therefore, generic design or installation procedures should be carefully reviewed and amended as required. The flow chart shown in Fig. 1 (principal phases summarized in Fig. 3) reflects the general sequence in which completion design and installation factors are typically studied. The "hook point" is provided as a reference point to which specific procedures, detailed later in this manual, will connect. The economic impact of designing and installing nonoptimized completions can be significant. Consequently the importance of completing a thorough design and engineering process must be stressed. Delaying the commencement 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 are important objectives, further reaching objectives, such as long-term profitability must not be ignored (Fig. 2). As is illustrated, a more complex and costly completion may provide a greater return over a longer period. In addition, the consequences of inappropriate design can have a significant effect, e.g., requiring premature installation of velocity string or artificial lift.

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Starting "philosophy statement"

Essential Basics • Safe • Efficient • Economic Logistic and Location • Surface and field facilities • Location and wellsite constraints

Establish the objectives and design basis

Corporate Policy • Medium and long-term objectives • Contractual requirements/obligations

Flowchart Key

Reservoir Parameters • Boundaries • Structure • Production mechanism • Dimensions • Rock Properties • Rock composition Reservoir Fluid Characteristics • Physical properties • Chemical properties Modelling and analyses • NODAL analyses • Perforation analyses • Others

Wellbore Construction • Drilling phase considerations • Evaluation phase considerations • Pre-completion stimulation Workover Philosophy • Routine well service requirements • Workover activities Material Selection • Forces on completion components • Wellbore environment constraints Review Alternative Completions • Compile list of alternatives/options • Confirm preferred completion type

Determine the optimum well performance

Establish conceptual completion designs

Budgetary Considerations • Investment incentives • Revenue(s) • Taxation Legislative and Regulatory • Safety and environmental factors Production Constraints • Downstream capacity • Flexibility of production • Production profile • Recoverability

Budgetary Analyses • Review outline completion costs

Technical requirements considerations and issues

Non-technical and commercial issues

Monitor Production Parameters • Actual vs. Forecast Evaluate Production Response • Actual vs. Forecast

Completion Evaluation

Final Budgetary Analyses • Actual vs. Forecast

Cleanliness standards • Completion components • Completion fluids Dimensional checks • Components • String * Space-out Equipment handling • Complex components • Thread make-up Proceedures • Assembly installation • Pressure testing • Space-out)

Pre-installation Well Service Work • Perform required treatments • Drift run (minimum/essential) Surface/Production Equipment • Preparation and checking

Component Installation

Onsite Preparation

Budgetary Analyses • Actual vs. planned Safety and Environmental Factors • Precaution and contingency planning Rig time and well downtime • Efficient completion

Budgetary Analyses • Actual vs. planned Safety and Environmental Factors • Precaution and contingency planning

Finishing "philosophy statement" Fig. 1a. Phases of well completion planning and installation. CONFIDENTIALITY This manual section is a confidential document which must not be copied in whole or in part or discussed with anyone outside the Schlumberger organisation.

Production Strategy (Well/Field) • Well performance • Field performance • Completion requirements

Completion Configuration • Wellbore tubulars • Wellbore and perforations • Near wellbore matrix • Hydraulic fracturing Production Initiation • Inducing flow • Clean-up program Completion Fluids • Required density • Chemical composition • Additives • Compatibility • Disposal Well Service and Workover • Completion function(s) • Light service units (wireline & CT) • Heavy service (snubbing and w/o rig) Surface Support Facilities • Utilities • Downstream facilities Modelling and Analyses • NODAL analyses • Others Perforating • SPAN* analyses • Charge and gun selection

Specific Procedures • Velocity string • Gas lift installation • ESP installation

POINT F OK

Develop detailed completion design

HO Local (Management) or Field Policy • Medium- to long-term objectives • Contractual requirements Implications of Multiple Well Project • Effect on cost • Operational conflict • Production conflict

Quality Assurance & Control • Component Inspection • Conformance to specified standards Prepare Installation Procedure(s) • Assembly • Installation • Testing • Contingency Plans Offsite Assembly • Check and test key components

Offsite Preparation

Confirm Project Timing • Lead times • Operational windows Quality Assurance & Control • Delivery time compliance • Quality documentation package/file

Client Convention and Preference • Existing stock • Contractual obligations • Corporate or local policies • Familiarity and acceptance Detailed 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)

Existing Completion Tubulars • Partial or complete removal • Preparation for concentric completion Select Treatments • Determined by specific conditions Prepare Procedures • Determined by application/conditions

Planning of associated service activities

Budgetary Analyses • Return on Investment

ES

Review strategy for well and field life

OCEDU R PR

PECIF IC RS O

Issue Bid Request or Enquiry • Technical specifications • Scope of work Bid Evaluation • Design proposal • Hardware selection • Technical support • Associated services • Innovative packaging (?) Recommendation • Technical merit • Integrated services Vendors Meeting • Confirm specifications/selection • Review/revise the scope of work Quality Assurance/Control • Inspection and verification • Controls and checks

Procure components and services

Issue Bid Request or Enquiry • Contractual non-technical content Bid Evaluation (Commercial) • Price/cost • Incentives/penalties • Innovative packaging Recommendation • Administrative Vendors Meeting • Establish contacts/form work group • Issue formal order Quality Assurance/Control • Non-technical controls and checks

Profile Enhanced Modification Recovery

Expenditure/Revenue

+$

Thru-tubing Stimulation W/O

Drilling, DST, completion logging and stimulation

P&A

Optimized production

Non-optimized production

-$ Time (Life of the well)

Fig. 2. Consequences of a non-optimized completion system.

ESTABLISH THE OBJECTIVES AND DESIGN BASIS PROCUREMENT OF COMPONENTS AND SERVICES DETERMINE THE OPTIMUM WELL PERFORMANCE PLANNING OF ASSOCIATED WELL SERVICE ACTIVITIES ESTABLISH CONCEPTUAL COMPLETION DESIGNS

OFFSITE PREPARATION

REVIEW STRATEGY FOR LIFE OF THE WELL AND FIELD

ONSITE PREPARATION

INSTALLATION DEVELOP DETAILED COMPLETION DESIGN EVALUATION

Fig. 3. Principal phases of well completion. CONFIDENTIALITY This manual section is a confidential document which must not be copied in whole or in part or discussed with anyone outside the Schlumberger organisation.

RESERVOIR PARAMETERS

Reservoir Boundaries

Reservoir Structure

Structural traps Staratographic traps Unconformities Permeability contrasts

Continuity Permeability barriers Isotropy

Production Mechanism

Physical Parameters

Water drive Solution gas Gas cap Combination Injection Artificial

Size Shape Height Pressure Temperature

Rock Properties

Rock Composition

Porosity Permeability Pore size distribution Fluid saturation Grain size and shape Wettability

Composition Consolidation Contamination Clay content Moveable fines Cementaceous material Scale forming materials

Fig. 4. Reservoir parameters. Reservoir Parameters The type of data outlined in this category are obtained by formation and reservoir evaluation programs such as coring, testing and logging. Typically, such data will be integrated by reservoir engineers to compose a reservoir model.

The reservoir structure, continuity and production drive mechanism are fundamental to the production process of any well. Frequently, assumptions are made of these factors which later prove to be significant constraints on the performance of the completion system selected.

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PRODUCED FLUID CHARACTERISTICS

Physical Properties

Chemical Properties

Oil density Gas gravity Viscosity Pour point Gas-oil ratio Water-oil ratio

Composition Wax content Asphaltenes Corrosive agents Toxic components Scale

Fig. 5. Produced fluid characteristics. Physical characteristics of the reservoir are generally more easily measured or assessed. Pressure and temperature are the two parameters most frequently used in describing reservoir and downhole conditions. The effects of temperature and pressure on many other factors can be significant. For example, corrosion rates, selection of elastomer or seal materials and the properties of produced fluids are all effected by changing temperature and pressure. When investigating the reservoir rock characteristics, the principal concern is assessing formation behavior and reaction. This includes behavior and reaction to the drilling, production or stimulation treatments which may be required to fully exploit the potential of the reservoir. The formation structure and stability should be closely investigated to determine any requirement for stimulation or sand control treatment as part of the completion process. The reservoir characteristics effecting completion configuration or component selection are best summarized by reviewing the reservoir structure, continuity, drive mechanism and physical characteristics. These should be reviewed alongside the physical and chemical properties of the formation (Fig. 4). Produced Fluid Characteristics

tion components and materials. These are chemical deposition (scale, asphaltenes etc.) and chemical corrosion (weight loss and material degradation). Both conditions still account for significant losses in production and degradation of equipment in many fields. The ability of the reservoir fluid to flow through the completion tubulars and equipment, including the wellhead and surface production facilities, must be assessed. For example, 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 completion system. While the downhole conditions contributing to these factors may occur over the lifetime of the well, consideration must be made at the time the completion components are being selected. Cost effective completion designs generally utilize the minimum acceptable components of an appropriate material. In many cases, reservoir and downhole conditions will change during the period of production. The resulting possibility of rendering the completion design or material unsuitable should be considered during the selection process. The production fluid characteristics effecting completion configuration or component selection are best summarized by reviewing the physical and chemical properties of the fluid (Fig. 5).

Two conditions, relating to the chemical properties of the produced fluid most effect the physical qualities of comple-

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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 completion design constraints. • Pre-completion stimulation or treatment – Final preparation of the wellbore through the zone of interest for the completion installation phase. It is an obvious requirement that the drilling program must be designed and completed within the scope and limits determined by the completion design criteria. Most obvious are the dimensional requirements determined by the selected completion tubulars and components. For example, if a multiple string completion is to be selected, an adequate size of production casing (and consequently hole size) must be installed. Similarly, the wellbore deviation or profile can have a significant impact.

Drilling and associated operations, e.g., cementing, performed 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 more cost effective, than the cure. Fluids used to drill, cement or service the pay zone should be closely scrutinized and selected 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 decisions concerning the technical feasibility and economic viability of possible completion systems will rest on the data obtained at this time. A pre-completion stimulation treatment is frequently conducted. This is often part of the evaluation process in a test-treat-test program in which the response of the reservoir formation to a stimulation treatment can be assessed. The wellbore characteristics affecting completion configuration or component selection are best summarized by reviewing the drilling, evaluation and pre-completion activities (Fig. 6).

WELLBORE CONSTRUCTION

Drilling

Pre-completion

Hole size Depth Deviation Well path Formation damage

Casing schedules Primary cementing Pre-completion stimulation Evaluation Logging Coring Testing Fluid sampling

Fig. 6. Wellbore construction

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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 of this manual to enlighten readers as to the true and necessary extent of the “completion program”. As has been demonstrated, considerable preparation, evaluation and design work has been completed before the completion tubulars and components are selected. With all design data gathered and verified, the completion component selection, assembly and installation process commences. This phase carries obvious importance since the overall efficiency of the completion system depends on proper selection and installation of components.

This is typically a time at which many people and resources are brought together to perform the operation. Consequently, the demands brought by high, and mounting daily charges imposes a sense of urgency which requires the operation be completed without delay. To ensure the operation proceeds as planned, it is essential that detailed procedures are prepared for each stage of the completion assembly and installation. The complexity and detail of the procedure is largely dependent on the complexity of the completion. In general, completion components are broadly categorized as follows. • Primary completion components

A “visionary” approach is necessary since the influence of all factors must be considered at this stage, i.e., factors resulting from previous operations or events, plus an allowance, or contingency, for factors which are likely or liable to effect the completion system performance in the future. The correct assembly and installation of components in the wellbore is as critical as the selection process by which they are chosen.

• Ancillary completion components Primary completion components are considered essential for the completion to function safely as designed. Such components include the wellhead, tubing string, safety valves and packers. In special applications, e.g., artificial lift, the components necessary to enable the completion system to function as designed will normally be considered primary components.

COMPLETION ASSEMBLY AND INSTALLATION

Primary Components

Ancillary Components

Wellhead Xmas tree Tubing Packer Safety valve

Circulating devices Nipples Flow couplings Injection mandrels Tubing seal assembly

Completion Fluids Completion fluid Packer fluid Perforating fluid Kick-off fluid

Fig. 7. Completion assembly and installation.

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Ancillary completion components enable a higher level of control or flexibility for the completion system. For example, the installation of nipples and flow control devices can allow improved control.

Initiating Production

Several types of device, with varying degrees of importance, can be installed to permit greater flexibility of the completion. While this is generally viewed as beneficial, a complex completion will often be more vulnerable to problems or failure, e.g., due to leakage.

• Kick-off

The desire for flexibility in a completion system stems from the changing conditions over the lifetime of a well, field or reservoir. For example, as the reservoir pressure depletes, gas injection via a side-pocket mandrel may be necessary to maintain optimized production levels.

The process of initiating flow and establishing communication between the reservoir and the wellbore is obviously closely associated with perforating operations. If the well is to be perforated overbalanced, then the flow initiation and clean up program may be dealt with in separate procedures. However, if the well is perforated in an underbalanced condition, the flow initiation and clean up procedures must commence immediately upon perforation.

A significant fluid sales and service industry has evolved around the provision of completion fluids. Completion fluids often require special mixing and handling procedures, since (i) the level quality control exercised on density and cleanliness is high, and (ii) completion fluids are often formulated with dangerous brines and inhibitors. The ultimate selection of completion components and fluids should generally be made to provide a balance between flexibility and simplicity. The completion component selection factors are best summarized by reviewing the primary and ancillary components, and installation procedures (Fig. 7).

The three stages associated with this phase of the completion process include (Fig. 8 and 9).

• Clean up • Stimulation

The benefits of underbalanced perforating are well documented and the procedure is now conducted on a routine basis. While the reservoir/wellbore pressure differential may be sufficient to provide an underbalance at time of perforation, the reservoir pressure may be insufficient to cause the well to flow after the pressure has equalized. Adequate reservoir pressure must exist to displace the fluids from within the production tubing if the well is to flow unaided. Should the reservoir pressure be insufficient to achieve this, measures must be taken to lighten the fluid

PRODUCTION INITIATION

Inducing Flow

Clean-up Program

Gas lift Nitrogen kick-off Light-fluid circulation Using completion components or coiled tubing

Initial flowrate and rate of increase Evaluation program Test–treat–test

Fig. 8. Production initiation.

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STIMULATION

Wellbore and Perforations

Near Wellbore and Reservoir Matrix

Wellbore clean-up Perforating acid Perforation wash

Matrix acidizing Hydraulic fracturing Non-acid treatments

Fig. 9. Stimulation column - typically by gas lifting or circulating less dense fluid. The preparations for these eventualities are part of the completion design process.

clean up treatment may be appropriate. There are a range of perforation treatments which may be associated with new or recompletion operations.

The flowrates and pressures used to exercise control during the clean up period are intended to maximize the return of drilling or completion fluids and debris. This controlled backflush of perforating debris or filtrate also enables surface production facilities to reach stable conditions gradually.

Perforating acids and treatment fluids are designed to be placed across the interval to be perforated before the guns are fired. Used in overbalanced perforating applications, the perforating acid or fluid reduces the damage resulting from the perforating operation. Perforation washing is an attempt to ensure that as many perforations as possible are contributing to the flow from the reservoir. Rock compaction, mud and cement filtrate and perforation debris have been identified as types of damage which will limit the flow capacity of a perforation, and therefore completion efficiency.

In some completion designs, an initial stimulation treatment may be conducted at this stage. An acid wash or soak placed over the perforations has proved effective in some conditions. However, as underbalanced perforating becomes more popular, the need and opportunity for this type of treatment has diminished. Stimulation There are four general categories of stimulation treatment which may be considered necessary during the process of completing a well. • Wellbore cleanup

If the objective of the treatment is to remove damage in or around the perforation, simply soaking acid across the interval is unlikely to be adequate. The treatment fluid must penetrate and flow through the perforation to be effective. In which case all the precautions associated with a matrix treatment must be exercised to avoid causing further damage by inappropriate fluid selection. Matrix treatment of the near wellbore area may be designed to remove or by-pass the damage. Hydraulic fracturing treatments provide a high conductivity channel through any damaged area and extending into the reservoir.

• Perforation washing or opening • Matrix treatment of the near wellbore area • Hydraulic fracturing Wellbore clean up will not normally be required with new completions. However, in wells which are to be reperforated or in which a new pay zone is to be opened, a well bore

Both matrix and hydraulic fracturing treatments require a detailed design process which is documented in the relevant Stimulation Manual.

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WELL SERVICE AND WORKOVER

Completion System Function

Heavy Workover Units

Well testing and routine monitoring Emergency kill and containment

Drilling rig Workover rig Combined CT and snubbing unit Light Service Units Slickline Electric wireline Coiled tubing Snubbing

Fig. 10. Well service and workover. Well Service and Maintenance Requirements The term “well servicing” is used (and misused) to describe 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 requirements must be considered during the completion design process. With more complex completion systems, the availability and response of service and support systems must also be considered (Fig.10). Wellbore geometry and completion dimensions determine the limitations of conventional slickline, wireline, coiled tubing or snubbing services in any application.

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LOGISTIC AND LOCATION CRITERIA

Surface Facilities

Location

Separator capacity Export capability Operational flexibility Disposal facility

Access to well Weather/climatic conditions Environmental constraints Proximity of neighboring interests

Fig. 11 Logistic and location criteria

Logistic, Location and Environmental Constraints

• Client familiarity and acceptance

Restraints imposed by logistic or location driven criteria often compromise the basic “cost effective” requirement of a completion system. Special safety and contingency precautions or facilities are associated with certain locations, e.g., offshore and subsea.

• Reliability and consequences of failure

A summary of the logistic, location and environmental constraints affecting completion design and configuration include well location, environmental conditions, weather conditions and adjacent land use (Fig 11).

Regulatory Requirements There are several regulatory and safety requirements applicable to well completion operations. These must generally be fully satisfied during both the design and execution phases of the completion process. • Provision for well-pressure and fluid barriers

Client Stock, Convention or Preference

• Safety and operational standards

The completion configuration and design must ultimately meet all requirements of the client. In many cases, these requirements may not be directly related to the reservoir, well or location (technical factors). An awareness of these factors, and their interaction with other completion design factors can help save time and effort in an expensive design process.

• Specifications, guidelines and recommendations • Disposal requirements • Emergency and contingency provisions

The following factors are common criteria which must be considered. • Existing material stocks or contractual obligation • Compatibility with existing downhole or wellhead components

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Revenue and Costs

Company Objectives

When completing an economic viability study, or comparison, the costs associated with each of the following categories should normally be investigated.

A measure of success can only be effectively made if there are clearly stated objectives. Such objectives may be macroscopic, but nonetheless will influence the specific objectives as applied to an individual well or completion. In addition, the wider company objectives may allow clarification of other selection factors, e.g., where two or more options offer similar or equal benefit, and no clear selection can be made on a technical basis.

• Production revenue • Capital cost (including completion component and installation cost) • Operating cost (including utilities and routine maintenance or servicing cost, also workover, replacement or removal cost.

• Desired payback period

The specific conditions, determined by the completion being studied, can be applied to enable a complete and representative cost analysis. In most cases, the order of importance is as shown, with the revenue stream being most critical.

• Recoverable reserves

• Cash flow

Installation costs are significant if special completion requirements impact the overall drilling or completion time. The actual cost of completion components is often relatively insignificant when viewed alongside the value of incremental production from improved potential or increased uptime. Economic The economic factors shown below are beyond the scope of technical preparation for well completion design. However, they undoubtedly influence the industry. Consequently a rudimentary understanding of the factors, and their interaction with factors previously discussed is beneficial. • Market forces (including seasonal fluctuations and swing production) • Taxation (including tax liability or breaks) • Investment availability

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