1、BRITISH STANDARDBS EN 15112:2006External cathodic protection of well casingsThe European Standard EN 15112:2006 has the status of a British StandardICS 23.040.99; 77.060g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40
2、g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 15112:2006This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2006 BSI 2006ISBN 0 580 49102 1National forewordThis British Standard was published by BSI. It is
3、the UK implementation of EN 15112:2006. It partially supersedes BS 7361-1:1991. BS 7361-1:1991 “Cathodic protection Part 1: Code of practice for land and marine applications”, which provides general information on cathodic protection, will be withdrawn when all the CEN standards relating to cathodic
4、 protection currently being prepared are published.The UK participation in its preparation was entrusted to Technical Committee 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
5、 necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN 15112July 2006ICS 23.040
6、.99; 77.060English VersionExternal cathodic protection of well casingsProtection cathodique externe des cuvelages de puits uerer kathodischer Korrosionsschutz vonBohrlochverrohrungenThis European Standard was approved by CEN on 19 June 2006.CEN members are bound to comply with the CEN/CENELEC Intern
7、al 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.Th
8、is 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
9、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 K
10、ingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2006 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15112:2006: EEN 1511
11、2:2006 (E) 2 Contents Page Foreword3 Introduction .4 1 Scope 5 2 Normative references 5 3 Terms and definitions .5 4 Description and assessment of corrosion risks 9 4.1 General9 4.2 Description of corrosion risks9 4.3 Corrosion risk assessment.9 5 Prerequisites for application of cathodic protection
12、 .10 5.1 General10 5.2 Electrical continuity.10 5.3 Electrical isolation .10 5.4 Cathodic protection equipment11 5.5 Groundbed11 5.6 Safety requirements 11 6 Design of the cathodic protection12 6.1 General12 6.2 Voltage drop profile method.12 6.3 Polarisation curve method13 6.4 Mathematical approach
13、 based on a field test .13 6.5 Simulation of the cathodic protection for a well 13 7 Measurement of the well-casing-to-soil potential at the wellhead .14 7.1 General14 7.2 Measuring points .14 7.3 Method used for potential measurement - Interpretation15 8 Additional cathodic protection equipment .15
14、 Annex A (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 Bibliography 36 EN 15112:2006 (E) 3 Foreword This docu
15、ment (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 identical text or by endorsement, at the latest by January 200
16、7, 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 Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
17、 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. EN 15112:2006 (E) 4 Introduction Gas, oil and water well casings are
18、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 between these. Steels in contact with the cement are in a passivation status and, thus, protected from any kind of externa
19、l 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 electroch
20、emical 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, particularly on recent wells, since most of them are well cemented. However, borehole cementation programmes sometimes r
21、esult 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 m
22、ay 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 whether or not to apply cathodic protection. EN 15112:2006 (E) 5 1 Scope This European Standard specifies methods used to
23、 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,
24、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
25、 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 refe
26、renced 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 60079-10:2
27、002) 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 cem
28、enting 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 str
29、ata; - 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
30、zone. There may be two or more strings of casing, one inside the other, in a single well: 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
31、 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 producti
32、on 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 betw
33、een 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
34、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 ap
35、plicable 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 tig
36、htness 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
37、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 EN 15112:2006 (E) 7 3.11 wellhead device installed at th
38、e 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 intervention on th
39、e different components of the well. This device allows a good electrical continuity between all the pipe strings EN 15112:2006 (E) 8 124531210635789Key 1 ground surface 2 surface casing 3 cementation 4 production casing 5 shoe 6 production annulus 7 tubing 8 liner (bottomhole) 9 packer (production)
40、10 intermediate casing Figure 1 Typical well completion equipment EN 15112:2006 (E) 9 4 Description and assessment of corrosion risks 4.1 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, wat
41、er, 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 consider
42、ed in order to decide if cathodic protection shall be applied to the structure. 4.2 Description of corrosion risks In general, for technical reasons, well casings should be covered by cement. In such conditions steel is passive, its potential is uniform under the cement and the corrosion hazards are
43、 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
44、 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 c
45、ells (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 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
46、 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 cementatio
47、n 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 i
48、s 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
49、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. EN 15112:2006 (E) 10 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 casin
