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
Published
Public Enquiry End Date
19-Mar-2021
Publication Date
11-May-2022
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
11-May-2022
Due Date
16-Jul-2022
Completion Date
12-May-2022

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SLOVENSKI STANDARD
SIST EN 15112:2022
01-julij-2022
Nadomešča:
SIST EN 15112:2006
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: EN 15112:2022
ICS:
25.220.40 Kovinske prevleke Metallic coatings
77.060 Korozija kovin Corrosion of metals
SIST EN 15112:2022 en,fr,de

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

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SIST EN 15112:2022
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SIST EN 15112:2022
EN 15112
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2022
EUROPÄISCHE NORM
ICS 23.040.99; 77.060 Supersedes EN 15112:2006
English Version
External cathodic protection of well casings

Protection cathodique externe des cuvelages de puits Äußerer kathodischer Korrosionsschutz von

Bohrlochverrohrungen
This European Standard was approved by CEN on 13 March 2022.

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. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 15112:2022 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN 15112:2022
EN 15112:2022 (E)
Contents Page

European foreword ............................................................................................................................................. 4

Introduction .......................................................................................................................................................... 5

1 Scope .......................................................................................................................................................... 6

2 Normative references .......................................................................................................................... 6

3 Terms and definitions ......................................................................................................................... 6

4 Cathodic protection personnel competence ............................................................................... 9

5 Description and assessment of corrosion risks .......................................................................10

5.1 General ....................................................................................................................................................10

5.2 Description of corrosion risks ........................................................................................................10

5.3 Corrosion risk assessment ...............................................................................................................11

5.3.1 Data collection during initial survey ............................................................................................11

5.3.2 Data collection during drilling .......................................................................................................11

5.3.3 Data collection in service .................................................................................................................11

5.3.4 Data collection during workover...................................................................................................12

6 Prerequisites for application of cathodic protection .............................................................12

6.1 General ....................................................................................................................................................12

6.2 Electrical continuity ...........................................................................................................................12

6.3 Electrical isolation ..............................................................................................................................13

6.3.1 General ....................................................................................................................................................13

6.3.2 Particular situations ..........................................................................................................................13

6.4 Cathodic protection equipment .....................................................................................................14

6.5 Groundbeds ...........................................................................................................................................14

6.6 Safety requirements ...........................................................................................................................14

7 Design of the cathodic protection .................................................................................................15

7.1 General ....................................................................................................................................................15

7.2 Voltage drop profile method ...........................................................................................................15

7.3 Polarization curve method ..............................................................................................................15

7.4 Simulation of the cathodic protection for a well ......................................................................16

7.5 Design based on historical data .....................................................................................................16

8 Measurement of the well-casing-to-soil potential at the wellhead ...................................16

8.1 General ....................................................................................................................................................16

8.2 Measuring points .................................................................................................................................16

8.3 Method used for potential measurement - Interpretation ..................................................17

8.4 CP System testing, commissioning and documentation ........................................................17

9 Additional cathodic protection equipment ...............................................................................18

10 CP System Monitoring, inspection and maintenance .............................................................18

Annex A (informative) Voltage drop profile ..........................................................................................19

A.1 General ....................................................................................................................................................19

A.2 Principle .................................................................................................................................................20

A.3 Method ....................................................................................................................................................20

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SIST EN 15112:2022
EN 15112:2022 (E)

A.4 Analysis of the curves ........................................................................................................................ 21

A.5 Practical considerations .................................................................................................................. 22

Annex B (informative) Polarization curve method applied to a well ........................................... 23

B.1 General ................................................................................................................................................... 23

B.2 Practical considerations .................................................................................................................. 24

Annex C (informative) Calculation of the potential shift at the bottom of the well casing and

the well casing to soil resistance ................................................................................................... 25

C.1 Purpose .................................................................................................................................................. 25

C.2 Principle ................................................................................................................................................. 25

C.3 Definition of terms and coefficients used in the equations ................................................. 26

C.3.1 Symbols and definitions ................................................................................................................... 26

C.3.2 Characteristics of a segment k ....................................................................................................... 28

C.3.3 Coefficients used in the attenuation equations ....................................................................... 28

C.4 Calculation - General attenuation equations ............................................................................ 29

C.4.1 General attenuation equations ...................................................................................................... 29

C.4.2 Method for solving the equations system .................................................................................. 29

C.4.3 Calculation procedure....................................................................................................................... 30

C.5 Calculation procedure example .................................................................................................... 31

Bibliography ....................................................................................................................................................... 34

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SIST EN 15112:2022
EN 15112:2022 (E)
European foreword

This document (EN 15112:2022) has been prepared by Technical Committee CEN/TC 219 “Cathodic

protection”, the secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by November 2022, and conflicting national standards shall

be withdrawn at the latest by November 2022.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 15112:2006.

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

— Requirements for CP personnel competences have been included.

— Additional requirements for insulation between the casing and other pipelines or well casings.

— In Annex A, the method to determine the CP current need has been simplified.

— Annex C (Calculation of the potential shift at the bottom of the well casing and the well casing to soil

resistance) has been revised.

Any feedback and questions on this document should be directed to the users’ national standards body.

A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: 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 the United

Kingdom.
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SIST EN 15112:2022
EN 15112:2022 (E)
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 can be in contact with more

or less aggressive layers. Furthermore, these surfaces can 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, cementation failures sometimes occur during the execution of borehole cementation

programmes, 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 can 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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SIST EN 15112:2022
EN 15112:2022 (E)
1 Scope

This document provides information on methods suitable for assessing the likelihood of leakage due to

external corrosion of well casings and to evaluate the need for cathodic protection, as well as methods of

providing cathodic protection to the external part of these wells in contact with the soil. It also defines

requirements for monitoring of performance of CP systems.

Onshore and offshore wells are included in the scope. However, for offshore wells where protection is

provided by anodes on the wellhead structure, it is recognized that it might not be practical to achieve

full protection of well casings.

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.

The general requirements of EN 12954 apply; this document details additional, specific, requirements for

CP of well casings.

This document applies to production and injection wells. References later in this document to production

also apply to injection.
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 https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
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SIST EN 15112:2022
EN 15112:2022 (E)
3.1
casing
well casing

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

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 geological layers;

— 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 enable the installation of 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.

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 layers
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.
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SIST EN 15112:2022
EN 15112:2022 (E)
3.5
completion

process, and its result, which consists of fitting a well with the production or injection tubing to allow

well operation in accordance with the applicable codes of practice and safety rules

3.6
electrical log survey
log recorded using an electrical wireline

Note 1 to entry: Electrical log survey can be pre construction well logs or post construction well logs.

3.7
flowline
pipe connecting a well to a gathering station
3.8
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
3.9
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.

3.10
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).

3.11
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
3.12
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.
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SIST EN 15112:2022
EN 15112:2022 (E)
Casing string for wells which include Casing string for wells which separate
production casing production tubing within casing
Key
1 ground surface 6 production annulus
2 surface casing 7 tubing
3 cementation 8 liner (bottom hole)
4 production casing 9 production packer
5 shoe 10 intermediate casing
Figure 1 — Typical well completion equipment
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.
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SIST EN 15112:2022
EN 15112:2022 (E)
5 Description and assessment of corrosion risks
5.1 General
Corrosion can occur on the external surface of well casings.

This corrosion, if not controlled, can 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 normally 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 can be in contact with the external medium. Macro-electrochemical cells

(steel/cement and steel/medium) can then be established and this can result in 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 can

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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SIST EN 15112:2022
EN 15112:2022 (E)
5.3 Corrosion risk assessment
5.3.1 Data collection during initial survey
Collection of the following data can assist in the risk assessment:

— the locations of the different geological layers the well will pass through (including any high-

resistivity layer that make it difficult to force current through underlying geological formation);

— the location of aquifers and type of water (fresh water that might require protection from

contamination, corrosive saline water, etc.);

— the corrosion history of existing well casing of the same material in the same general area or in

similar environments. The history should include cumulative leak frequency and downhole data

obtained from workovers (reconditioning) records;

— the nature or constituents of the product being produced or injected in the well;

— location of the well casing system (e.g. if in a sparsely or densely populated area);

— location of the well casing system as related to other facilities;
— influence of DC sources foreign to the well system and DC stray currents.

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.
5.3.2 Data collection during drilling

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 geological layer

changes.

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

electrical log surveys which have been recorded in the open borehole.
5.3.3 Data collection in service

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 current discharge from the casing and hence

corrosion. Furthermore, according to the voltage drop observed, it is possible to determine the corrosion

current density on the exterior surface of corroding casing. This allows determination of 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.
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SIST EN 15112:2022
EN 15112:2022 (E)

Before production, there are many well logging techniques that can be, and often are, employed primarily

to inform the production capability of the reservoir, but which can provide significant information on the

likely corrosion risks within specific geological layers. During a corrosion risk assessment any records of

well logging should be accessed and expert opinion sought in respect of the significance and

interpretation of the data.

In addition, any existing outputs from post construction well logs, and any record of corrosion, or section

loss, shall be assessed.
5.3.4 Data collection during workover
Collection of the following data can assist in the risk assessment:
— voltage drop profile (Annex A);
— electromagnetic casing thickness measurements.

Data collected during electrical log surveys can also be useful in assessing CP requirements.

6 Prerequisites for application of cathodic protection
6.1 General

For onshore well casings, the requirements defined in EN 12954 apply, except for the exemptions

explicitly stated herein. Specifically:
— The potential protection criteria;

— The method of assessment of cathodic protection adequacy. Alternative methods as described in this

document can be used:
• voltage drop profile method;
• the polarization curve method, mathematical modelling;
• density of discharged current;
• corrosion history of existing well casing;

— It might not be appropriate to implement a temporary CP system for the well casing.

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.
For offshore well casings, EN 12473 does not apply.
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
...

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.

---------------------- Page: 1 ----------------------
oSIST prEN 15112:2021
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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.
---------------------- Page: 3 ----------------------
oSIST prEN 15112:2021
prEN 15112:2021 (E)
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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oSIST prEN 15112:2021
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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
...

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