Well Completion Planning con't lec ( 4 )

Drilling

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.

Evaluation

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.

Pre-Completion

 A precompletion 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..

Completion Assembly
and Installation

With all design data gathered and verified, the completion component selection,
assembly and installation process commences. This phase carries importance
since the overall efficiency of the completion system depends on proper
selection and installation of 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 affect 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. This is typically a
time at which many people and resources are brought together. The demands
brought by high and mounting, daily charges imposes a sense of urgency
which requires the operation to 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.

Primary Completion
Components
Primary completion components

 are considered essential for the completion to
function safely as designed. Such components include the safety valves, gas
lift equipment, tubing flow control tools 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 System 

Several types of devices, 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).
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 selection of completion
components and fluids should reflect a balance between flexibility and simplicity.

Completion Assembly
and Installation Factors

Completion Fluids

A significant fluid sales and service industry has evolved around the provision
of completion fluids. Completion fluids often require special mixing and hauling
procedures, since (a) the level of quality control exercised on density and
cleanliness is high and (b) completion fluids are often formulated with
dangerous brines and inhibitors.

Initiating Flow

The process of initiating flow and establishing communication between the
reservoir and the wellbore is closely associated with perforating operations. If
the well is to be perforated overbalanced, (higher pressure in the wellbore than
in the formation) 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, (lower pressure in the wellbore than in the formation)
the flow initiation and clean up procedures must commence immediately upon
perforation.Production Initiation

Underbalanced
Perforating

Perforating when the reservoir pressure is substantially higher than the wellbore
pressure is referred to as under-balanced perforating. 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. In the event the reservoir
pressure is insufficient to achieve this, measures must be taken to lighten the
fluid column typically by gas lifting or circulating a less dense fluid.
The flow rates 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.

Wellbore Clean Up

Wellbore cleanup is normally not required with new completions. However, in
wells which are to be re-perforated or in which a new pay zone is to be opened,
a well bore clean up treatment may be appropriate. There is a range of perforation
treatments associated with new or recompletion operations.

Overbalanced
Perforating

Perforating when the wellbore pressure is higher than the reservoir pressure is
referred to as Overbalanced Perforating. This is normally used as a method of
well control during perforating. The problem with this method is it introduces
wellbore fluid into the formation causing formation damage.
It is sometimes desirable to place acid across the interval to be perforated when
overbalanced perforating. The resulting inflow of acid results is a matrix type
acid treatment occurring.

Extreme Overbalance
Perforating

In this type of perforating operation the wellbore is pressured up to very high
pressures with gas (usually nitrogen). When the perforating guns are detonated
the inflow of high pressure gas into the formation results in a mini-frac, opening
up the formation to increase inflow.

Stimulation Treatments

Acid Washing
of Perforations

Perforation acid 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.
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.

Hydraulic Fracturing

Hydraulic fracturing treatments provide a high conductivity channel through
any damaged area and extending into the reservoir. The natural fractures
within the formation material are opened up using hydraulic fluid pressure.
Commonly a proppont such as sand is introduced to ‘prop’ the fracture open
after the pressure is removed, but still will allow flow of reservoir fluids and
gases. Hydraulic fracturing treatments require a detailed design process which
is usually performed by the service supplier.

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 (through-tubing)
•  Major workovers (tubing pulled)
•  Emergency containment or response

Well service and 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.
Well bore geometry and completion dimensions determine the limitations of
conventional slick line, wireline, coiled tubing or snubbing services in any
application.

Logistic and
Location Constraints

Restraint 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).

Logistic and
Location Criteria

Client Requirements

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.
The following factors are common criteria which must be considered:

•  Existing stock or contractual obligation
•  Compatibility with existing downhole or wellhead components
•  Client familiarity and acceptance
•  Reliability and consequences of failure

Regulatory Requirements

There are several regulatory and safety requirements applicable to well
completion operations. These must 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 provision

Revenue and Costs

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

•  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)
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 Factors

A rudimentary understanding of the economic factors is beneficial.

•  Market forces (including seasonal fluctuations and swing

production)

•  Taxation (including tax liability or tax breaks)
•  Investment availability

Company Objectives

A measure of success can only be made if there exists clearly stated objectives.
Such objectives may 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 factors, (e.g., where two or
more options offer similar or equal benefit and no clear selection can be made
on a technical basis).

•  Desired payback period
•  Cash flow
•  Recoverable reserves

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