prEN 15112

External cathodic protection of well casings

This document specifies methods used to evaluate the external corrosion hazards of well casings, as well as cathodic protection means and devices to be implemented in order to prevent corrosion of the external part of these wells in contact with the soil.
This document applies to any gas, oil or water well with metallic casing, whether cemented or not.
However, in special conditions (shallow casings: e.g. 50 m, and homogeneous soil), EN 12954 can be used to achieve the cathodic protection and assess its efficiency.

Äußerer kathodischer Korrosionsschutz von Bohrlochverrohrungen

Dieses Dokument legt Verfahren fest, die angewendet werden, um die äußeren Korrosionsgefahren von Bohrlochverrohrungen zu bewerten, sowie kathodische Schutzmaßnahmen und Geräte, die einzusetzen sind, um zu verhindern, dass der äußere Teil dieser Bohrlöcher, der das Erdreich berührt, korrodiert.
Dieses Dokument gilt für jedes Gas-, Öl- oder Wasserbohrloch mit metallischer Verrohrung, unabhängig davon, ob sie einzementiert ist oder nicht.
Unter besonderen Bedingungen jedoch (flache Verrohrung: z. B. 50 m und homogenes Erdreich) kann EN 12954 angewendet werden, um kathodischen Korrosionsschutz zu erreichen und dessen Wirksamkeit zu beurteilen.

Protection cathodique externe des cuvelages de puits

Le présent document a pour objet de présenter les méthodes permettant d'évaluer les risques de corrosion externe des cuvelages de puits, ainsi que les moyens et dispositifs de protection cathodique à mettre en oeuvre pour prévenir la corrosion de la partie extérieure de ces puits en contact avec le sol.
Le présent document s'applique à tous les puits de gaz, de pétrole ou d'eau à cuvelage métallique, cimenté ou non.
Néanmoins dans certaines conditions particulières [cuvelages de faible profondeur (par exemple 50 m) et sols homogènes], l’EN 12954 peut être utilisée pour réaliser la protection cathodique et évaluer son efficacité.

Zunanja katodna zaščita globinskih zaščitnih cevi

General Information

• Status: Not Published
• ICS: 23.040.99 - Other pipeline components
• ICS: 77.060 - Corrosion of metals
• Technical Committee: CEN/TC 219 - Cathodic protection (provisional)
• Drafting Committee: CEN/TC 219/WG 1 - Cathodic protection of buried and immersed metallic structures
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Due Date: 28-Sep-2021
• Completion Date: 28-Sep-2021
• Ref Project: oSIST prEN 15112:2021 - External cathodic protection of well casings

RELATIONS

• Revised: EN 15112:2006 - External cathodic protection of well casings
• Effective Date: 08-Jul-2020

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 15112:2021
01-marec-2021
Zunanja katodna zaščita globinskih zaščitnih cevi
External cathodic protection of well casings
Äußerer kathodischer Korrosionsschutz von Bohrlochverrohrungen
Protection cathodique externe des cuvelages de puits
Ta slovenski standard je istoveten z: prEN 15112
ICS:
25.220.40 Kovinske prevleke Metallic coatings
77.060 Korozija kovin Corrosion of metals
oSIST prEN 15112:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 15112:2021
DRAFT
EUROPEAN STANDARD
prEN 15112
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2021
ICS 23.040.99; 77.060 Will supersede EN 15112:2006
English Version
External cathodic protection of well casings

Protection cathodique externe des cuvelages de puits Äußerer kathodischer Korrosionsschutz von

Bohrlochverrohrungen

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 219.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15112:2021 E

worldwide for CEN national Members.
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Contents Page

1 Scope .......................................................................................................................................................... 5

2 Normative references .......................................................................................................................... 5

3 Terms and definitions ......................................................................................................................... 5

4 Cathodic protection personnel competence ............................................................................... 8

5 Description and assessment of corrosion risks ......................................................................... 8

5.1 General...................................................................................................................................................... 8

5.2 Description of corrosion risks ......................................................................................................... 8

5.3 Corrosion risk assessment ................................................................................................................ 9

6 Prerequisites for application of cathodic protection............................................................... 9

6.1 General...................................................................................................................................................... 9

6.2 Electrical continuity ............................................................................................................................. 9

6.3 Electrical isolation .............................................................................................................................. 10

6.3.1 General.................................................................................................................................................... 10

6.3.2 Particular situations .......................................................................................................................... 10

6.4 Cathodic protection equipment ..................................................................................................... 11

6.5 Groundbed ............................................................................................................................................. 11

6.6 Safety requirements .......................................................................................................................... 11

7 Design of the cathodic protection ................................................................................................. 12

7.1 General.................................................................................................................................................... 12

7.2 Voltage drop profile method ........................................................................................................... 12

7.3 Polarization curve method .............................................................................................................. 12

7.4 Simulation of the cathodic protection for a well ..................................................................... 13

8 Measurement of the well-casing-to-soil potential at the wellhead .................................. 13

8.1 General.................................................................................................................................................... 13

8.2 Measuring points ................................................................................................................................ 13

8.3 Method used for potential measurement - Interpretation .................................................. 14

9 Additional cathodic protection equipment ............................................................................... 15

Annex A (normative) Voltage drop profile ............................................................................................ 16

A.1 Scope ........................................................................................................................................................ 16

A.2 Principle ................................................................................................................................................. 17

A.3 Method .................................................................................................................................................... 17

A.4 Practical considerations ................................................................................................................... 19

Annex B (informative) Polarization curve method applied to a well ........................................... 20

B.1 Scope ........................................................................................................................................................ 20

B.2 Practical considerations ................................................................................................................... 21

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European foreword

This document (prEN 15112:2021) has been prepared by Technical Committee CEN/TC 219 “Cathodic

Protection”, the secretariat of which is held by BSI.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 15112:2006.

In comparison with the previous edition, the following technical modifications have been made:

— Requirements for CP personnel competences are included.

— Additional requirements for insultation between the casing and other pipelines / well casings. For

the design, a mathematical approach has been added.
— In Annex A, the method to determine the CP current need has been simplified.

— Annex C (Calculations for determining potential shift at the bottom of a cathodically protected well

casing) has been deleted.
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Introduction

Gas, oil and water well casings are usually cemented for the purpose of anchoring the pipes in the

borehole and isolating the various geological layers from each other. This is necessary to avoid liquid

exchanges between these.

Steels in contact with the cement are generally passivated, and thus, protected from external corrosion,

except if the cement contains chloride ions. However, it is not always possible to obtain a continuous

cementation on all the external steel surfaces. These bare residual surfaces may be in contact with more

or less aggressive layers. Furthermore, these surfaces may constitute electrochemical cells with the

cemented metallic parts. The anodic areas, which are the poorly cemented parts, correspond to corrosion

areas.

In general, external corrosion effects are rare, particularly on recent wells, since most of them are well

cemented. However, borehole cementation programmes sometimes result in cementation failures, and

studies have shown that, corrosion phenomena being progressive, the mean time for the appearance of

leaks is dependent on different factors such as geological formation, thickness of the layers and of the

steel casing.

Experience has also shown that the situation may be significantly improved by applying external cathodic

protection to the well casings.

Environmental aspects with regard to gas, oil or water wells should be considered when deciding on

whether or not to apply cathodic protection.
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1 Scope

This document specifies methods used to evaluate the external corrosion hazards of well casings, as well

as cathodic protection means and devices to be implemented in order to prevent corrosion of the external

part of these wells in contact with the soil.

This document applies to any gas, oil or water well with metallic casing, whether cemented or not.

However, in special conditions (shallow casings: e.g. 50 m, and homogeneous soil), EN 12954 can be used

to achieve the cathodic protection and assess its efficiency.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

EN 12954, General principles of cathodic protection of buried or immersed onshore metallic structures

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
casing
well casing

heavy steel pipe string used to line a borehole from the ground surface, and secured in the formations

generally by cementing

Note 1 to entry: Casing is generally externally cemented over its total depth or over a length sufficient to obtain

anchoring and stability between the production or storage zone and the ground surface or other intermediate

layers.
This pipe string function is:
— to prevent the ingress of fluid from upper strata;

— to keep the hole from collapsing due to the pressure of the geological layers crossed;

— to isolate the inside part of the well from the surrounding soil;
— to continue drilling to the production or storage zone;

— to drive down the tubing string from the surface to the production or storage zone.

There may be two or more strings of casing, one inside the other, in a single well:

— surface casing: casing that extends from the surface to a depth sufficient to avoid any entering of surface waters

or earth into the well;

— intermediate casing: casing set from the ground surface down to an intermediate depth. This intermediate casing

terminates in the intermediate casing shoe and the production casing extends below it to the production or storage

zone;

— production casing: casing that extends through the surface casing and intermediate casing to the production or

storage zone. The extremity of the production casing can be at the top or bottom of this zone.

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3.2
cellar

excavation at ground surface, intended for housing the wellhead and safety shut-off devices

EXAMPLE safety valves
3.3
cementation

process, and its result, which ensures the anchoring of well casing in the borehole and the tightness

between different geological levels
Note 1 to entry: In the same time, this cementation can mitigate corrosion
3.4
centralizer

device constituted by a set of metallic blades which are fitted around the pipes of a string to keep them

centred, either in the open hole (hole drilled in the ground), or inside pipes of larger diameter in which

the considered string is installed

Note 1 to entry: This device can also be used to ensure electrical continuity between the two concentric pipe

strings.
3.5
completion

process, and its result, which consists of fitting a well with the tubing to allow well operation in

accordance with the applicable codes of practice and safety rules
3.6
flowline
pipe connecting a well to a gathering station
3.7
liner
bottom hole liner

pipe having the same function as the casing but hung inside a casing (or another liner) and not at the

wellhead like a conventional casing
3.8
packer
production packer
device ensuring tightness of a pipe annulus

Note 1 to entry: The production packer seals the annulus between the tubing and the production casing or liner.

3.9
shoe
guide shoe

cylindrical element attached to the lower part of the casing, and allowing to place the casing in the

borehole

Note 1 to entry: If equipped with a valve, it makes the borehole cementation easier (cementing shoe).

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3.10
tubing
production tubing

pipe string, with its additional equipment, inside the production casing to allow the flow of oil, gas or

water between the production or storage zone and the ground surface
3.11
wellhead

device installed at the top of the well, designed to hang the different pipe strings and to ensure tightness

between the various annular spaces
Note 1 to entry: See Figure 1.

Note 2 to entry: The wellhead is fitted with valves to allow access (pressure monitoring, sampling) to the different

annuli. Such fitted wellhead allows well operation and the intervention on the different components of the well. This

device allows a good electrical continuity between all the pipe strings.
Key
1 ground surface 6 production annulus
2 surface casing 7 tubing
3 cementation 8 liner (bottom hole)
4 production casing 9 packer (production)
5 shoe 10 intermediate casing
Figure 1 — Typical well completion equipment
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4 Cathodic protection personnel competence

Personnel who undertake the design, supervision of installation, commissioning, supervision of

operation, measurements, monitoring inspection, and supervision of maintenance of cathodic protection

systems shall have the appropriate level of competence for the tasks undertaken.

EN ISO 15257 constitutes a suitable method of assessing competence of cathodic protection personnel.

Competence of cathodic protection personnel to the appropriate level for tasks undertaken can be

demonstrated by certification in accordance with prequalification procedures such as EN ISO 15257 or

by another equivalent scheme.
5 Description and assessment of corrosion risks
5.1 General
Corrosion may occur on the external surface of well casings.

This corrosion, if not controlled, may lead to harmful damage such as losses of products, water, gas or oil,

damage to the well and its completion (internal equipment), damage to the environment, for instance in

allowing exchange between different geological formations. There is also the possibility of harm for

people living near such installations.

The risks of corrosion should be considered in order to decide if cathodic protection shall be applied to

the structure.
5.2 Description of corrosion risks

In general, for technical reasons, well casings should be externally encapsulated by cement. In such

conditions steel is passive, its potential is uniform under the cement and the corrosion hazards are

reduced. In this case, cathodic protection should not be necessary.

In fact, due to the heterogeneity of the soils which are crossed during drilling and specifically due to the

heterogeneity of the mechanical properties of these soils, it is not always possible to guarantee that a

continuous cement layer covers the whole steel surface. Because of this non-homogeneous cement layer,

some parts of the casing surface are in contact with the external medium. Macro-electrochemical cells

(steel/cement and steel/medium) are then established and this results in a corrosion of the anodic parts

of the cells (steel in the medium).

If there is no electrical isolation between the well and surface piping, such detrimental macro-cells may

also appear between the casing and the bare or poorly coated parts of the buried structure surface which

become the anodic parts of the macro-cell.

Corrosion caused by the currents generated by macro-cells is more severe where soil layers with low

resistivity are crossed.
Risks of corrosion damage shall be considered particularly where:

— the designed service life is long (depending on location, operational conditions);

— the procedure and execution of the cementation results in areas not, or incorrectly, cemented;

— there are stray current sources;
— the geological layers crossed are of a different nature.
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5.3 Corrosion risk assessment

The previous information is only intended to provide the general principles of the corrosion risks

involved.

Usually, part of a corrosion risk assessment for buried steel is by measuring the structure-to-electrolyte

potential. However, these potential measurements require placement of a reference electrode in the

electrolyte in the immediate vicinity of the metal. For a well casing, access is limited to the upper part of

the well and it is thus impossible to perform any direct casing/soil potential measurement on the deep

borehole.

During drilling, samples of drill cuttings should be checked and recorded at regular depths, particularly

if the make-up of the drill cuttings changes, to assess corrosivity and composition if the strata changes.

As an alternative to the above method, another way could be to carry out an accurate analysis of the

electric log surveys which have been recorded in the open borehole.

Another approach consists in establishing whether current coming from the outside environment

(ground) enters in or, conversely, exits from the casing, by using the method known as voltage drop

profile (Annex A), which allows this determination by following the direction and intensity of currents

circulating in the casing along the well.

This method allows localization of all areas where there is corrosion. Furthermore, according to the

voltage drop observed, it is possible to assess the importance of the current intensity exiting from the

casing, which determines the rate of corrosion. Nevertheless, this method is difficult to implement.

If available, the usual logs performed after borehole cementation can be usefully analysed to ascertain

quality and homogeneity of the borehole cementation, especially in the areas with low electrical

resistivity.
6 Prerequisites for application of cathodic protection
6.1 General

The requirements defined in EN 12954 shall be met. However, it should be taken into account that the

well casing is bare and in contact with the soil in the borehole through the cement.

6.2 Electrical continuity

If a well is to be cathodically protected, a number of precautions shall be taken during completion. In

addition to the external parts in contact with the borehole cementation or the soil, for which protection

is required, the well generally includes other parts which are not in contact with the surrounding soil.

The latter comprise the production string and all or part of intermediate and production casings

depending on the type of completion, operation mode, the depth and the diameter.

It is necessary to avoid current flow through an electrolyte located in the annular space, since it could

cause corrosion. Annular spaces which are not cemented are generally filled with a liquid which may be

brine, mud water and so on. Under such conditions, current flow through the electrolyte shall be

prevented by the use of bonds between each string.
Therefore it is necessary:

— to establish or prove the presence of metallic bonds to ensure perfect electrical continuity between

each casing part, at upper (wellhead) and lower (shoe) levels, and

— to install or prove the presence of metallic centralizers where geological layers may promote a flow

of current into the casing.
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If electrical continuity between production casing and the other casings and liners is not assured, it

may be necessary to undertake a full well workover and introduce metallic spacers of a design to

ensure electrical continuity between the various tubulars, before cathodic protection is applied.

NOTE 1 Workovers interrupt production and are complex operations to implement.

NOTE 2 It is possible to inspect tubing withdrawn during a workover and determine distribution and extent

of external corrosion.
6.3 Electrical isolation
6.3.1 General

In principle, there should be no electrical continuity between the well to be protected and the foreign

structures and particularly the flowline. For this purpose, electrical isolation should be installed between

the well and the flowline. Particular precautions are required to mitigate risks of incendive sparks caused

by the electrical isolation (e.g. by inadvertent bridging of the isolation or electrical surges such as

lightning).

In this case, a special attention shall be given to avoid undesirable electrical shunts which may be caused

by metallic bonds due to the small diameter pipes which are used for well control and safety devices.

Another problem may appear when the fluid or a part of the fluid conveyed in the flowline is a low-

resistivity electrolyte. An internal corrosion risk may exist due to a possible voltage drop between both

sides of the isolating joint. In such a case, the isolating joint shall be internally coated with a suitable and

electrically isolating material. Moreover, the internal coating shall be:

— applied over a suitable length to reduce the corrosion rate to an acceptable level;

— applied only on the side with the most negative potential.
6.3.2 Particular situations

Sometimes it may be necessary to ensure electrical continuity (direct or resistive) between the well to be

protected and neighbouring structures, typically the flowlines.

— This may be the case for some wells remote from any electrical current source. A method to allow

the well cathodic protection consists in the use of the flowline as a return conductor by short

circuiting the isolating joint. Then, the protection is carried out on both structures. However, as both

structures have very different coating resistances, it may be necessary to fit the bond of the isolating

joint with a resistor.

— This may be also the case if the well is subject to the influence of stray currents. The bonding of the

isolating joint (with or without resistor) can sometimes allow the installation of a current drainage

system on the flowline to mitigate the influence of the stray currents.

— Wells have very low resistance against earth. A device to protect the isolating joint against over

voltages should be installed if such a risk exists.

In some cases, it may be impossible to insulate the well from foreign structures. Such is the case for

offshore platforms where wells are always connected to the main structure and receive cathodic

protection current from the structure cathodic protection system.
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6.4 Cathodic protection equipment

Considering the low resistance to earth of the casing and its length, and thus the high current demand, it

is generally only possible to obtain protection down to the well shoe by use of impressed current even

when borehole cementing is of good quality.

Offshore, where it is difficult to obtain potentials more negative than - 1,00 V measured with an Ag / AgCl

/ sea water reference electrode at the wellhead, whatever the platform protection method, the borehole

cementing needs to be of very good quality to protect the entire casing.

For installations affected by stray currents, suitable equipment (e.g. current drainage bonds) shall be

considered.

Whatever the method selected, the cathodic protection equipment shall be chosen and provided in

accordance with EN 12954.
6.5 Groundbed

To allow the protective current to reach the lower extremity of the well, the groundbeds should be at a

sufficient distance from the casing in order to obtain a good current distribution. The distance depends

on:

— soil resistivity between the groundbed and the well casing and along the depth of the well casing;

— amount of protective current (dimensions of the well casing and cementing quality);

— depth of the well casing.
6.6 Safety requirements

The national and local safety rules and procedures concerning gas, crude oil and water drilling

installations, shall be complied with.

These rules and procedures concern surface installations, wells and equipment related to these

structures. They may cover the following:
— electrical insulation;
— permanent or temporary earthing;

— perfect electrical continuity throughout the installations to avoid any sparking risk, even during

maintenance and workovers;
— materials and equipment;

— classified hazardous areas, according to EN 60079-10-1, where it is possible to install cathodic

protection equipment both with regard to access to the wellhead and any explosion risk.

A close co-operation between specialists on safety and cathodic protection shall be established to comply

with the safety rules as well as cathodic protection requirements (assurance of its correct installation and

operation, as well as absence of influence risks for neighbouring buried metallic parts which are not

protected by means of cathodic protection).
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7 Design of the cathodic protection
7.1 General

In general, design of the cathodic protection of a structure includes as a first step the definition of the

minimum initial of protective current demand required to meet the basic criterion for cathodic protection

E ≤ E ’ as defined in EN 12954).

However, as mentioned above (Clause 5) it is impossible to verify that this basic criterion for cathodic

protection of well casings is correctly fulfilled along the entire structure to be protected.

Consequently, to begin the study of cathodic protection of a well, it is necessary to use methods and

measurement procedures specific to this type of structure.

The methods described hereafter allow the determination of the currents required for cathodic

protection. Other methods, based on specialist experience, may be used, if they are documented and can

lead to a comparable result.
7.2 Voltage drop profile method

This method, as mentioned in 5.2 for corrosion risk assessment and described in Annex A, may be used

to determine the protective current to ensure effective cathodic protection. The aim of this method is to

make sure that all segments of the voltage drop profile have a positive slope which means that the entire

structure no longer has anodic areas.

For this purpose, a temporary cathodic protection station is installed. The temporary groundbed should

be far away from the well to allow a good distribution of the current. Groundbed selection shall take

account of safety, particularly electrical hazards, for the personnel in charge of tests and also for the

structure under test.
For a chosen protective current, the voltag
...