Wellbore Completion Concepts

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PCB 3043

DRILLING AND PRODUCTION TECHNOLOGY

WELLBORE COMPLETION CONCEPTS

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COURSE CONTENT

Bottom hole completion techniques

Completion string Components

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Bottom hole completion must satisfy the following

objectives:

Provision of optimum production/injection performance.

Ensure safety.

Maximize the integrity and reliability of the completion

over the envisaged life of the completed well.

Minimize the total costs per unit volume of fluid

produced or injected, i.e. minimize the costs of initial

completion, maintaining production and remedial

measures.

Can also fulfill specific objective, i.e. sand control, etc.


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After drilling engineers have drilled the borehole to the

zone of interest, the communication between reservoir

and borehole has to be initiated. Therefore, bottom

hole completion need to be accomplished before the

completion of the drilling operations.


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There are 3 approaches for the completion of the

reservoir zone:

OPEN HOLE COMPLETION

SCREEN OR PRE-SLOTTED LINER COMPLETIONS

CEMENTED AND PERFORATED CASING/ LINER

COMPLETIONS


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The simplest approach is to leave the entire drilled reservoir section

open after drilling.

Sometimes referred to as “barefoot” completions and the

technique is widely applied.

No equipment requires to be installed, savings in both costs and

time.

The entire interval is open to production and provides no real

selective control over fluid production or injection.

Not recommended for wells where distinctive variations in layeral

permeability.

This lack of zonal control for production or injection is a major

limitation on the application of this technique.

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Open hole completions should only be applied in

consolidated formations

Currently open hole completions are applied in a

range of environments:

a) Low cost / multi well developments

b) Deep wells, consolidated with depletion drive

c) Naturally fractured reservoirs

d) Some horizontal and multi lateral wells

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Once the drilling through completed reservoir section has

been completed, a wire-wrapped screen or steel pipe which

has slots or alternative sand control screen.

The principal purpose of the screen or liner is to prevent

any produced sand from migrating with the produced fluids

The success of the completion in controlling sand

production is dependent upon the screen or slot sizes and

the sand particle sizes.

Slots may quickly become plugged and impede flow

resulting in a loss in productivity.

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This system is sometimes used in inclined/high angle angles to

prevent major borehole collapse or facilitate the passage of

logging tools.

This technique also suffers from the same inability for zonal

control and may only effectively control sand.

Low cost technique since the cost of a screen to cover the

reservoir interval is much less than the cost of a casing,

cementing and perforating.

An alternative to the open hole completion in situations where

the reservoir rock consists of relatively large and homogenous

sand grains.

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CEMENTED AND PERFORATED CASING/ LINER COMPLETIONS


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The final choice is to install either a casing string which

extends back to surface or a liner which extends back into

the shoe of the previous casing string, which would then be

cemented in place by the displacement of a cement slurry

into the annular space between the outside wall of the

casing and the borehole wall.

To provide flow paths for fluid to enter the wellbore from

the formation, or vice versa, the casing and cement sheath

will be perforated at selected locations using explosive

charges contained in a perforating gun.

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The integrity and selectivity of the completion depends to a

great extent on an effective hydraulic seal being located in

the casing-formation annulus by the cement.

Greater costs and time than the previous options. (cost of

casings, cost of perforating, cementing and the additional

time necessary to complete the borehole)

Ability to control zones efficiently!!, thus will enhance

reservoir management capabilities.

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CASING STRINGS


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CASING STRINGS


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GENERAL WELL COMPLETION STRING

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Basic Completion String Components:

X-mas tree

Wellhead

SSSV

Side Pocket Mandrel

Sliding Side Door

Packer

Seal Assembly

Packer

Nipple

Perforated join

Wireline entry guide

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X-MAS TREE and WELLHEAD

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WELLHEAD

The wellhead provides the basis for the mechanical construction of the well at surface or the sea-bed, such as:

Suspension of all individual casing and tubular, concentrically in the well

Ability to install a surface closure/flow control device on top of the well namely:

A blow out preventer stack whilst drilling

A Xmas tree for production or injection

Hydraulic access to the annuli between casing to allow cement placement and between the production casing and tubing for well circulation

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X-MAS TREE

The purpose of the Xmas tree is to provide valve

control of the fluids produced from or injected into

the well.

The Xmas tree is normally flanged up to the

wellhead system after running the production

tubing.

All outlets have valves which are manually operated.

In the isolated case, the valve may be controlled

hydraulically.

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PACKERS

Mechanically set Hydraulically set


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Packers can provide annular seal or pack-off in production

wells was necessary for one of the following reasons:

To improve flow stability and production control

Protection of the outer containment system/equipment

such as the production casing and the wellhead.

To provide the facility to select or isolate various zones

during stimulation or production, e.g. to isolate two

producing zones having different fluid properties, GOR,

pressure or permeability (especially relevant for injection)

or to stimulate or pressure maintenance.


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Packer has three requirements:

1. It should be connected to the tubing.

2. Its OD (outer diameter) should be sufficiently

less than the ID (inner diameter) of the casing to

provide clearance for running in the hole.

3. It must be designed so that when it is in the

proper position, some surface control can be

used to cause it to seal off the annulus between

the tubing and casing.


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The pack-off is accomplished by

expanding or extending the elastomer

element outwards from the packer

body until it contacts the casing wall.

Two Types:

Retrievable Packer which, can be

easily retrieved after installation.

Permanent Packer which, as its

name indicates, cannot be easily

retrieved. To retrieve the packer it

is necessary to mill away the

packer internal sleeves to allow the

rubber element to collapse.


PACKERS

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SSSV


Their function is to provide

remote sub-surface

isolation in the event of a

catastrophic failure of the

Xmas tree or as a failsafe

shutdown system

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SIDE POCKET MANDREL


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SLIDING SIDE DOORS


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NIPPLE

Special joint of tubing used near the bottom of the tubing


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In the selection of the method, a range of considerations may influence the choice including:

Cost

Flow stability

Ability to control flow and

Ensure well safety or isolation; ensuring that the integrity of the well will not be compromised by corrosion or erosion.

SELECTION OF THE FLOW CONDUIT

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For a single zone completion, the following alternatives exist:

1. Tubingless casing flow

2. Casing and tubing flow

3. Tubing flow with/without annular isolation


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Figures showing different Completions


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Tubingless casing flow.

Advantages:

Fast, simple and minimizes costs

Disadvantages:

Flow area is so large that the fluid superficial velocities are low enough for phase separation and slippage to occur,

Only applicable for high rate wells.

The fluid is in direct contact with the casing and this couldresult in any of the following:

Casing corrosion, if H2S or CO2 are present in produced fluids.

Casing erosion, if sand is being produced.

Potential burst on the casing at the wellhead if the well changed from oil to gas production.

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Casing and tubing flow

Advantages:

Good for highly productive wells

providing a circulation capability deep in the well where reservoir fluids can be displaced to surface

removes the necessity for re-injectioninto the reservoir

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Tubing flow with annular isolation

Advantages:

Good for all types of wells

The most widely used

Offers maximum well security and control

Disadvantages:

Does not provide a circulation capability because of packer

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BASIC WELL SCHEMATIC

Completion string facilities

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These are the essential attribute of completion stringinstallations:

The ability to contain anticipated flowing pressure and any hydraulic pressures which may be employed in well operations and conduct fluid to surface (production) or the reservoir (injection wells) with minimal flowing pressure loss and optimal flow stability.

The ability to isolate the annulus between the casing and the production tubing if flow instability is likely or it is desirable to minimize reservoir fluid contact with the production casing.


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In the event that isolation at surface is not possible, the ability is needed to shut-in down-hole either by remote control or directly activated by changing well flowing conditions.

A means to communicate or circulate(selectively when required) between the annulus and the tubing.

A provision for physical isolation of the tubing by the installation of a plug to allow routine isolation e.g. for pressure testing of the tubing.

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Multiple Zone completions

Multiple zone completions are employed on reservoirs where more than one distinct reservoir layer is to be produced by a single well and for which the requirement is to produce these layers separately.

Concepts

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Multiple zone completions is categorized as follows:

1. Co-mingled Flow (Flow from various zone)

More than one zone flows into the tubing string

2. Segregated-Multiple Zone Flow

Use multiple production conduit within the same well-bore; requires one tubing for one production zone


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1. Co-mingled Flow (Flow from various zone)


Advantages

Low capital investment needed as more than one zone produced from

one tubing string

Drilling cost is minimized

Disadvantages

Mixing of produced fluids in the wellbore can be disadvantageous if one or

more fluid have any of the following characteristics

-Corrosive material, e.g. acids, H2S, CO2

-When one of the zone is producing sand.

-When fluids have been different hydrocarbon compositions

-Different WOR and GOR as this would influence vertical lift performance

Injection of stimulation fluid cannot be diverted easily into individual layer

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2. Segregated-Multiple Zone Flow


Advantages

Production rate from each zone can be independently control

Changes in production characteristics of one zone will not affect other

zone

Stimulation can be applied to each zone

Disadvantages

Since each zone needs a tubing string and other completion

equipment, additional expenditure and installation time is needed

The possibility of component failure is increased with the amount of

completion equipment.

Using of two small tubing sizes to fit in production casing string may

reduce total flow capacity of the well

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Configurations

Dual Zone Completion

Casing/Tubing Flow

Dual Tubing Flow

Single String Selected Producer

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Casing/Tubing Flow

Single tubing string is run with a

single packer installed to

provide isolation between

zones.

One zone will produce up the

tubing, while other will produce

up the casing tubing annulus.

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Casing/Tubing Flow

This configuration needs

one tubing string, two

packers and a crossover tool

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Dual Tubing Flow

In this type of completion, a separate tubing string for

each zone is to be installed with two packers; one to

isolate between zones and the other to upper zone

from the upper casing annulus

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Single String Selected Producer

In this type of completion, the well is

completed over two zones, utilizing

one tubing string designed to

selectively allow the production of

either zone.

The completion requires two

packers; one to isolate between

zones and the other to isolate the

annulus.

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Triple Zone Completion

Utilizing separate zonal flow into one of three tubing

strings (having three packers for isolation)

Two string completion whereby flow from two zones

is co-mingled into one of the tubing strings

Single zone annular flow and two tubing strings

producing separately from two zones

Single string, triple zone selected completion

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Four or More Producing Zones

Single string selective producer

Dual string selective producer

Triple string with annular production

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Equipment Equipment requirements for multiple completions are largely

based on the equipment available for single string completions

with the following exceptions:

1. Tubing hanger systems

2. Tubing packer systems

3. Special installation equipment

The number of tubing strings will affect the completion

procedure

Sizes of tubing and other ancillary equipment are limited by

casing inside diameter, tensile load and torque capabilities

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Dual Completion Split Hanger Dual tubing hanger integral

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Packers; dual and triple configuration

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COMPLETION NO.1

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COMPLETION NO.2

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COMPLETION NO.3

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COMPLETION NO.4

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COMPLETION NO.5

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COMPLETION NO.6

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COMPLETION NO.7

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COMPLETION NO.8

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COMPLETION NO.9

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COMPLETION NO.10

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Documents

Wellbore Completion Concepts