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:
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.
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.
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
- Acquire wellbore survey and reservoir test data used to
- Prepare the wellbore through the zone of interest for the
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
- Ensure cost efficient installation and reliable operation
Phase II:
Completion Component
Selection and Installation
Completion Component
Selection and Installation
The proper selection and installation of completion components is required.
Components may be broadly categorized as follows:
balance between flexibility and simplicity.
Phase III:
Initiating Production
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
Production Evaluation
and Monitoring
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
- Verification that assumptions made during the design process
- Trends or statistical departures which may provide early
or workover
- Periodic monitoring of reservoir parameters provides useful
recompletion as required by reservoir depletion