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1、BRITISH STANDARD BS EN 15112:2006 External cathodic protection of well casings The European Standard EN 15112:2006 has the status of a British Standard ICS 23.040.99; 77.060 ? Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI BS EN 15112:2006 This British Standard was published under the
2、authority of the Standards Policy and Strategy Committee on 31 October 2006 BSI 2006 ISBN 0 580 49102 1 National foreword This British Standard was published by BSI. It is the UK implementation of EN 15112:2006. It partially supersedes BS 7361-1:1991. BS 7361-1:1991 “Cathodic protection Part 1: Code
3、 of practice for land and marine applications”, which provides general information on cathodic protection, will be withdrawn when all the CEN standards relating to cathodic protection currently being prepared are published. The UK participation in its preparation was entrusted to Technical Committee
4、 GEL/603, Cathodic protection. A list of organizations represented on GEL/603 can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard ca
5、nnot confer immunity from legal obligations. Amendments issued since publication Amd. No. DateComments Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 15112 July 2006 ICS 23.040.99; 77.060 English Version External cathodic protection
6、of well casings Protection cathodique externe des cuvelages de puitsuerer kathodischer Korrosionsschutz von Bohrlochverrohrungen This 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 gi
7、ving 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 Central Secretariat or to any CEN member. This European Standard exists in three official ver
8、sions (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 Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium,
9、 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 STANDARDIZATI
10、ON COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: rue de Stassart, 36 B-1050 Brussels 2006 CENAll rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 15112:2006: E Licensed Copy: :FULLNAME, : DATE, Uncontrolle
11、d Copy, (c) BSI EN 15112:2006 (E) 2 Contents Page Foreword3 Introduction.4 1Scope 5 2Normative references5 3Terms and definitions .5 4Description and assessment of corrosion risks 9 4.1General9 4.2Description of corrosion risks9 4.3Corrosion risk assessment.9 5Prerequisites for application of cathod
12、ic protection.10 5.1General10 5.2Electrical continuity.10 5.3Electrical isolation.10 5.4Cathodic protection equipment11 5.5Groundbed11 5.6Safety requirements 11 6Design of the cathodic protection12 6.1General12 6.2Voltage drop profile method.12 6.3Polarisation curve method13 6.4Mathematical approach
13、 based on a field test.13 6.5Simulation of the cathodic protection for a well 13 7Measurement of the well-casing-to-soil potential at the wellhead.14 7.1General14 7.2Measuring points.14 7.3Method used for potential measurement - Interpretation15 8Additional cathodic protection equipment .15 Annex A
14、(normative) Voltage drop profile16 Annex B (informative) Polarisation curve method applied to a well23 Annex C (informative) Determination by calculation of the potential shift at the bottom of the well and the well to soil resistance26 Bibliography36 Licensed Copy: :FULLNAME, : DATE, Uncontrolled C
15、opy, (c) BSI ? EN 15112:2006 (E) 3 Foreword This document (EN 15112:2006) 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 identic
16、al text or by endorsement, at the latest by January 2007, and conflicting national standards shall be withdrawn at the latest by January 2007. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Stand
17、ard: 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. Licensed Copy:
18、 :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 4 Introduction Gas, oil and water well casings are usually cemented for the proposes of anchoring the pipes in the borehole and isolating the various geological layers from each other. This is necessary to avoid liquid exchanges betw
19、een these. Steels in contact with the cement are in a passivation status and, thus, protected from any kind of 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 residua
20、l 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 poor cemented parts, correspond to corrosion areas. In general, external corrosion effects are rare, pa
21、rticularly 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
22、 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 wells. Environmental aspects with regard to gas, oil or water wells should be considered when deciding on whe
23、ther or not to apply cathodic protection. Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 5 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 implem
24、ented 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
25、 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 refe
26、renced 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 s
27、tructures 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 fol
28、lowing 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 anchorin
29、g 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 p
30、art 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: Licensed Copy: :FULLNAME, : D
31、ATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 6 - 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 intermediat
32、e 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
33、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,
34、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 instal
35、led. 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-lin
36、e 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 th
37、e 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 (produ
38、ction 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 Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 7 3.11 wellhead device installe
39、d at the top of the well, designed to hang the different pipe strings and to ensure tightness between the various annular spaces. The wellhead is fitted with valves to allow access (pressure monitoring, sampling) to the different annuli. Such fitted wellhead allows well operation and the interventio
40、n on the different components of the well. This device allows a good electrical continuity between all the pipe strings Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 8 1 2 4 5 3 1 2 10 6 3 5 7 8 9 Key 1 ground surface 2 surface casing 3 cementation 4 production cas
41、ing 5 shoe 6 production annulus 7 tubing 8 liner (bottomhole) 9 packer (production) 10 intermediate casing Figure 1 Typical well completion equipment Licensed Copy: :FULLNAME, : DATE, Uncontrolled Copy, (c) BSI ? EN 15112:2006 (E) 9 4 Description and assessment of corrosion risks 4.1 General Corrosi
42、on 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 differen
43、t 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. 4.2 Description of corrosion risks In general, for technical reasons, wel
44、l casings should be covered 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
45、 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 me
46、dium. 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 isolating joint between the well and surface piping, such detrimental macro-cells may also appear between the
47、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 parti
48、cularly 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. 4.3 Corrosi
49、on 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