Well Completion Planning lec ( 3 )

Introduction

Planning a completion, from concept through to installation, is a complex
process comprising many phases. Many factors must be considered, although
in most cases, a high proportion can be quickly resolved or disregarded.
Regardless of the completion design complexity, the basic requirements of any
completion must be kept in mind throughout the process. A completion system
must provide a means of oil or gas production (or injection) which is safe,
efficient, reliable and economical.
Ultimately, it is the predicted technical efficiency of a completion system, viewed
alongside the company objectives that will determine the configuration and
components to be used.

Completion

Planning Process

This section outlines the principal factors to be considered when planning an
oil or gas well completion. In addition to the technical influences on completion
design and selection, economic and non-technical issues are also detailed.
The relevance of these issues, in common with technical details, is dependent
upon 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 is based on the individual requirements of each well. Therefore, it is
necessary to review and amend generic design or installation procedures as
required.

Principal Phases of

Well Completion Design

Impact of
Non-Optimized
Completions

The economic impact of designing and installing non-optimized completions
can be significant. Consequently, the importance of completing a thorough
design and engineering process must be stressed. Delaying the commencement
of the wells pay out period is one example of how non-optimized completion
design, or performance, can affect the achievement of objectives. However,
while reducing installation cost and expediting start-up are important objectives,
far-reaching objectives such as long-term profitability must not be ignored. As
illustrated, a more costly and complex 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).

Optimized Completion
System

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 is 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.
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 affected by changing temperature and pressure.

Components of a
Reservoir Model

Produced Fluid
Characteristics

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 cause
unacceptable back-pressure, thereby dramatically reducing the efficiency of
the completion system.
Although the downhole conditions contributing to these factors may occur
over the lifetime of the well, they must be considered 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.

Components of Produced
Fluid Characteristics

Wellbore Construction

The drilling program must be designed and completed with 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.

Components of
Wellbore Construction

Introduction To Completions lec ( 2 )

Naturally Flowing Completions

Wells completed in reservoirs which are capable of producing without assistance

are typically more economic to produce. However, in high-temperature, highpressure

applications, a great deal of highly specialized engineering and design

work will be required to ensure that safety requirements are met.

In general, naturally flowing wells require less complex downhole components

and equipment. In addition, the long-term reliability and longevity of the

downhole components is generally better than that of pumped completions.

In many cases, wells may be flowed naturally during the initial phases of their

life, with some assistance provided by artificial lift methods as the reservoir is

depleted. Such considerations must be reviewed at the time of initial completion

to avoid unnecessary expense and interruption of production.

Artificial Lift Completions

All pumped, or artificially lifted, completions require the placement of

specialized downhole components. Such components are electrically or

mechanically operated, or are precision engineered devices. These features

often mean the longevity or reliable working life of an artificial lift completion

is limited. In addition, the maintenance or periodic workover requirements

will generally be greater than that of a naturally flowing completion.

Artificial Lift Methods

Pumped or assisted lift production methods currently in use include the

following:

•  Gas lift
•  Electric submersible pump
•  Plunger lift
•  Hydraulic or Jet Pump
•  Variable Cavity Pump (VCP)
•  Hydraulic or Jet pump
•  Progressive cavity pump (PCP)

Single Zone Completion

 In single zone completions, it is relatively straight forward to produce and

control the interval of interest with the minimum of specialized wellbore or

surface equipment. Since typically one conduit or tubing string in involved,

the safety, installation and production requirements can be easily satisfied.

In most single zone completions, a packer (or isolation device) and tubing

string is used. This provides protection for the casing or liner strings and

allows the use of flow control devices to control production.

The complexity of the completion is determined by functional requirements

and economic viability. Several contingency features may be installed at a

relatively minor cost at the time of the initial installation. Consequently,

consideration must be given to such options during the initial design phase.

Multiple Zone Completions

Multiple zone completions are designed to produce more than one zone of

interest. However, there are many possible configurations of multiple zone

completion, some of which allow for selective, rather than simultaneous

production.

Phases of Well Completion

A sequential and logical approach to the design and execution process is
required. Since the ultimate efficiency of a completion is determined by
operations and procedures executed during almost every phase of a wells life,
a continual review and monitoring process is required. Typically this can be
summarized as follows:

Accurate Data is Essential

As in all design and execution processes, the acquisition of accurate or
representative data is essential. The level of accuracy required will vary with
the data type from the assumption of essential reservoir formation and fluid
properties to more general properties, which can more easily be measured.

Establish Objectives and Design Criteria

This initial phase may be summarized as the collection of data pertaining to
the reservoir, wellbore and production facility parameters. This data is
considered alongside constraints and limitations which may be technical or
non-technical in nature (e.g., company policy).
Some flexibility may be required, especially in exploration or development
wells, where there are several unknown or uncertain parameters.
The principal factors affecting the performance of any well relate to the three
areas illustrated in below. Of these, many of the fluid and reservoir properties
can be measured or inferred from measurements. Almost all elements of a
completion can be designed and an appropriate selection will thus affect well
performance.

Principal Factors Affecting a Well’s Performance

Pre-Completion: Constructing The Wellbore

The principal completion objectives of this phase include:

•  Efficiently drill the formation while causing the minimum

practical near-wellbore damage

•  Acquire wellbore survey and reservoir test data used to

identify completion design constraints

•  Prepare the wellbore through the zone of interest for the

completion installation phase (run and cement production
casing or liner and preparation for sand control or
consolidation services)

Phase I: Design Objectives

The optim design is fundamental for the projected life of the well. The objectives
for which a completion system is designed vary. However, the following points
may be regarded as fundamental and will have some bearing in any application:

•  Ensure the potential for optimum production (or injection)
•  Provide for adequate monitoring or servicing
•  Provide some flexibility for changing conditions or applications
•  Contribute to efficient field/reservoir development and

production

•  Ensure cost efficient installation and reliable operation

Phase II:
Completion Component
Selection and Installation

The proper selection and installation of completion components is required.
Components may be broadly categorized as follows:

In general, the optimum completion configuration (and system) will provide a
balance between flexibility and simplicity.

Phase III:
Initiating Production

In most cases, this phase of the completion process is further subdivided into
the following three stages:

 Phase IV:
Production Evaluation
and Monitoring

An initial production evaluation is necessary to confirm that the completion
system fulfills the production capabilities required by the design objectives.
Subsequent evaluation and monitoring exercises will provide the following
information on the reservoir, well and completion system:

•  Statistics relating to the reliability and longevity of completion

components

•  Verification that assumptions made during the design process

were accurate or representative

•  Trends or statistical departures which may provide early

indication of completion problems or the need for intervention
or workover

•  Periodic monitoring of reservoir parameters provides useful

data for the completion and production of offset wells or
recompletion as required by reservoir depletion

 

Introduction To Completions lec ( 1 )

Introduction

After a well has been drilled, it must be properly completed before it can be
put into production. A complex technology has evolved around the techniques
and equipment developed for this purpose. The selection of such equipment
and techniques should only be made following a thorough investigation of the
factors which are specific to the reservoir, well and production system under
study.

Three Basic Requirements

 

There are three basic requirements of any completion, in common with almost
every oil field product or service.

A completion system must provide a means of oil or gas production (or injection) which is:

 

•  Safe
•  Efficient / Economic
•  Reliable 

Completion System Requirements

Current industry conditions may force operators to place undue emphasis on
the economic requirement of completions. However, a non-optimized system
may compromise long term company objectives. For example, if the company
objective is to maximize the recoverable reserves of a reservoir or field, a poor
or inappropriate completion design can seriously jeopardize achievement of
the objective as the reservoir becomes depleted.
In short, it is the technical efficiency of the entire completion system, viewed
alongside the specific company objectives, which ultimately determines the
completion configuration and equipment used.

Definition of Well Completion

Well completion involves a process which extends far beyond the installation
of wellbore tubulars and equipment. To highlight this fact, the following
definition of the term “completion” is presented:

• Completion: The design, selection and installation of tubulars,

         tools and equipment located in the wellbore for the purpose of
         conveying, pumping or controlling production or injection fluids.

Under this definition, installing and cementing the production casing or liner,
as well as logging, perforating and testing, are part of the completion process.
In addition, complex wellhead equipment and processing or storage
requirements affect the production of a well and so may have some bearing on
the design and configuration of the completion.

History and Evolution of Oil and Gas Well Completions

As the understanding of reservoir and production performance has evolved,
then so too has the systems and techniques put in place as part of the completion
process.
Early wells were drilled in very shallow reservoirs which were sufficiently
consolidated to prevent caving. As deeper wells were drilled, the problems
associated with surface water prompted the use of a casing or conductor to
isolate water and prevent caving of the wellbore walls. Further development
of this process led to fully cased wellbores in which the interval of interest is
perforated.
Modern completions are now commonly undertaken in deep, hot and difficult
conditions. In all cases, achieving the completion and eventual production
objectives are a result of careful planning and preparation.

Completion Types

 

There are several ways of classifying or categorizing completion types. The
most common criteria for the classification of completions include the
following:

• Wellbore/reservoir interface, i.e., open-hole or cased hole, horizontal completion

•  Producing zones, i.e., single zone or multiple zone production

•  Production method, i.e., natural flowing or  artifically induced production (Artificial Lift)

Open Hole or Barefoot Completions

Barefoot completions are only feasible in reservoirs with sufficient formation
strength to prevent caving or sloughing. In such completions there are no
means of selectively producing or isolating intervals within the reservoir or
open hole section. The production casing or liner is set and cemented in the
reservoir cap rock, leaving the wellbore through to the reservoir open.
The use of open hole completions is now restricted primarily to some types of
horizontal wells and to wells where formation damage from (air drilling) drilling
fluids is severe. To prevent an unstable formation from collapsing and plugging
the wellbore, slotted screen or perforated liners may be placed across the open
hole sections.

Example of Openhole Completions

Perforated Completions

The evolution and development of efficient and reliable perforating tools and
logging services has enabled complex completions to be designed with a high
degree of efficiency and confidence. Modern perforating charges and
techniques are designed to provide a clear perforation tunnel through the
damaged zone surrounding the wellbore. This provides access to the undamaged
formation, allowing the reservoir to be produced to its full capability.
Cased and cemented wells generally require less complex pressure control
procedures during the early stages of installing the completion components.
Efficient reservoir interpretation and appraisal techniques combined with a
high degree of depth control, enables selective perforating. This helps ensure
the successful completion and production of modern-day oil and gas wells by
precisely defining which zones of the reservoir will be opened for flow.
Multiple zone completions are often used in reservoirs with complex structures
and production characteristics. The ability to select and control the production
(or injection) of individual zones is often the key to ensuring the most efficient
production regime for the field or reservoir. Consequently, modern multiple
completions may be complex but maintain a high degree of flexibility and
control of production.

Examples of Cased Hole Completions

 continued

 

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