EN 15112:2006

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.External cathodic protection of well casingsProtection cathodique externe des cuvelages de puitsÄußerer kathodischer Korrosionsschutz von BohrlochverrohrungenTa slovenski standard je istoveten z:EN 15112:2006SIST EN 15112:2006en25.220.40Kovinske prevlekeMetallic coatingsICS:SLOVENSKI
STANDARDSIST EN 15112:200601-oktober-2006

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15112July 2006ICS 23.040.99; 77.060 English VersionExternal cathodic protection of well casingsProtection cathodique externe des cuvelages de puitsÄußerer kathodischer Korrosionsschutz vonBohrlochverrohrungenThis European Standard was approved by CEN on 19 June 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15112:2006: E

Voltage drop profile.16 Annex B (informative)
Polarisation curve method applied to a well.23 Annex C (informative)
Determination by calculation of the potential shift at the bottom of the well and the well to soil resistance.26 Bibliography.36

1 Scope This European Standard 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 European Standard applies to any gas, oil or water well with metallic casing, whether cemented or not. However, in special conditions (shallow casing: e.g. 50 m, and homogeneous soil), EN 12954 can be used to achieve the cathodic protection and assess its efficiency. This European Standard also describes techniques allowing determination of the current required for protection and ensuring correct operation of the cathodic protection devices installed. 2 Normative references The following referenced documents are indispensable for the application 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 12954:2001, Cathodic protection of buried or immersed metallic structures — General principles and application for pipelines EN 60079-10, Electrical apparatus for explosive gas atmospheres — Part 10: Classification of hazardous areas (IEC 60079-10:2002) 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN 12954 and the following apply (see also Figure 1). 3.1 casing (or well casing) heavy steel pipe string used to line a borehole from the ground surface, and secured in the formations generally by cementing NOTE 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 allows: - 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 depth is situated between the surface casing shoe and 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 levels.
NOTE 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. 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 flow-line pipe connecting a well to a station 3.7 liner (bottom hole) 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) device ensuring tightness of a pipe annulus. The production packer seals the annulus between the tubing and the production casing or liner 3.9 shoe cylindrical element attached to the lower part of the casing, and allowing to place the casing in the borehole (guide shoe). If equipped with a valve, it makes easier the borehole cementation (cementing shoe) 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

12453 1210635789
Key 1
ground surface 2 surface casing 3
cementation 4
production casing 5
shoe 6
production annulus 7
tubing 8
liner (bottomhole) 9
packer (production) 10 intermediate casing Figure 1 — Typical well completion equipment

- 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. 4.3 Corrosion risk assessment The previous information is only intended to provide a general idea on the corrosion risks involved. Usually, a corrosion risk is assessed by measuring the structure-to-electrolyte potential. However, these potential measurements require installation 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 measurement on the deep borehole. During drilling, samples of drill cuttings should be checked and recorded at regular depths, particularly if their make up changes, to assess corrosivity and composition if the strata changes.

- 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, 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). 6 Design of the cathodic protection 6.1 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 ≤ Ep’ as defined in the European Standardization (see EN 12954). However, as mentioned above (Clause 4) it is impossible to verify that the 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. 6.2 Voltage drop profile method This method, as mentioned in 4.2 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 has to be installed. The temporary groundbed should be far away from the well to allow a good repartition 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 voltage drop is recorded along the entire well in accordance with the procedure described in Annex A. If the protective current used during this test is not sufficient (Annex A, Figure A.2, case B), the voltage drop, recorded at each measuring point with the measuring tool shows negative slope segments. These represent those areas which remain anodic. This is always the case if the voltage drop shows negative values. If the protective current used during the test is sufficient (Annex A, Figure A.2, case C), all segments of the curve of potentials have a positive slope. The entire well structure is cathodic. In some cases, the test may be performed again with a lower current to determine the minimum protection current which makes the entire structure cathodic.
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