wellbore completion concepts

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PCB 3043

Well Design & Completion

WELL COMPLETION CONCEPTS

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Design & completion of both production and injection 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.

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

Introduction

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Introduction

Four (4) principal decision needed for fundamental design of completion:

1.Bottom hole completion technique

2.Production conduit selection

3.Completion string facilities

4.Multiple Zone Completions

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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.

Bottom hole completion techniques

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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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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 PRODUCTION CONDUIT

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For a single zone completion, the following alternatives exist:

1. Tubingless casing flow2. Casing and tubing flow3. 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 could

result 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-injection into 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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21BASIC 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.

Completion string facilities

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Completion string facilities 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.

General Completion String

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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 FlowUse 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)


AdvantagesLow capital investment needed as more than one zone produced from one tubing stringDrilling cost is minimized

DisadvantagesMixing 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


AdvantagesProduction rate from each zone can be independently controlChanges in production characteristics of one zone will not affect other zoneStimulation can be applied to each zone

DisadvantagesSince each zone needs a tubing string and other completionequipment, additional expenditure and installation time is neededThe 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 tubingstrings (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 stringsproducing 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 bycasing 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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wellbore completion concepts

Documents

open hole completion

hole completion technique2

costs of initial completion

completion string facilities4

sand production

fluid production

produced sand

reservoir zone