1、 Standard Practice Application of Cathodic Protection for External Surfaces of Steel Well Casings This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, wh
2、ether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise,
3、to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restrictio
4、n on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of
5、 this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE Inte
6、rnational standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety pro
7、blems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consu
8、ltation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time in a
9、ccordance with NACE technical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision. The user is cautioned to
10、 obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone +1 281/228-6200).
11、 Reaffirmed 2007-03-10 Reaffirmed 2001-09-20 Reaffirmed September 1984 Approved March 1986 NACE International 1440 South Creek Drive Houston, TX 77084-4906 +1 281/228-6200 ISBN:1-57590-134-X 2007, NACE International NACE SP0186-2007 (formerly RP0186-2001) Item No. 21031 SP0186-2007 NACE Internationa
12、l i _ Foreword Oil and gas wells represent a large capital investment. It is imperative that corrosion of well casings be controlled to prevent loss of oil and gas, environmental damage, and personnel hazards, and in order to ensure economical depletion of oil and gas reserves. This NACE Internation
13、al standard practice identifies procedures to determine the need for cathodic protection (CP) and the current requirements to achieve CP of well casings associated with oil and gas production and gas storage. It also outlines practices for the design and installation of CP systems and for their oper
14、ation and maintenance. The purpose of this standard is to ensure more effective prevention of corrosion of well casings by making available reliable information about CP as it relates to well casings. This standard is intended for use by corrosion engineers in oil and gas production, especially thos
15、e concerned with the CP of steel well casings. This standard was originally prepared in 1986 by Unit Committee T-1E on Cathodic Protection and Task Group (TG) T-1J-2, a component of Unit Committee T-1J on Storage Wells. It was reaffirmed in 1994 by Unit Committee T-1E, and in 2001 and 2007 by Specif
16、ic Technology Group (STG) 35 on Pipelines, Tanks, and Well Casings. The STG membership consists of representatives from oil and gas producing and storage companies, equipment manufacturers, consulting firms, and CP service companies. Included in the membership are persons involved in design, consult
17、ing, research, construction, maintenance, and manufacturing and supply of materials, all of whom are concerned with the establishment and maintenance of cathodic protection systems used with well casings. This standard is issued by NACE under the auspices of STG 35. In NACE standards, the terms shal
18、l, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something considered good and is recommended but is not man
19、datory. The term may is used to state something considered optional. _ SP0186-2007 ii NACE International _ NACE International Standard Practice Application of Cathodic Protection for External Surfaces of Steel Well Casings Contents 1. General 1 2. Definitions 1 3. Determination of Need for CP . 4 4.
20、 Criterion for CP and Current Requirements 5 Bibliography for Section 4 6 5. Design of CP Systems for Well Casings . 7 Bibliography for Section 5 9 6. Installation of CP Systems 10 7. Control of Interference Currents 11 Bibliography for Section 7 13 8. Operation and Maintenance of CP Systems . 13 9.
21、 Corrosion Control Records 14 References 16 Appendix A: Casting Potential Profile (Nonmandatory) . 16 Appendix B: E- Log I Test (Nonmandatory) 19 Appendix C: Electromagnetic Casing Inspection Instruments (Nonmandatory) . 21 Appendix D: Well Completion Design and Other Factors Associated with CP (Non
22、mandatory) 23 TABLES Table C.1Instrument Effectiveness . 22 FIGURES Figure A1Casing Potential Profile Tool 17 Figure A2Typical Casing Potential Profile Plot 18 Figure B1Equipment Set-Up for E-Log-I Test 20 Figure B2Sample E-Log-I Plot . 21 _ SP0186-2007 NACE International 1 _ Section 1: General 1.1
23、This standard presents acknowledged procedures for the control of external corrosion of steel well casings by applying CP. This standard is intended to be a guide for establishing minimum requirements for corrosion control when CP is practical and cost-effective. 1.2 This standard does not designate
24、 practices for specific situations. The complexity of some casing spacing, subsurface proximity to other casings, and environmental conditions preclude standardizing the application of CP. Deviation from this standard may be warranted in specific situations, provided those in responsible charge can
25、demonstrate that the objectives expressed in this standard have been achieved. 1.3 This standard does not include corrosion control methods based on chemical control of the environment. 1.4 This standard applies only to well casing exteriors and not to internal corrosion, or to corrosion of other su
26、rface or downhole equipment. 1.5 The provisions of this standard should be applied under the direction of competent persons knowledgeable in the physical sciences, principles of engineering, and mathematics. They may have acquired knowledge by professional education and related practical experience
27、and should be qualified to practice corrosion control for well casings by the use of CP. Such persons may be registered professional engineers recognized as being qualified as corrosion specialists in the appropriate fields of corrosion control by NACE International. Their professional activities sh
28、ould include suitable experience in well casing corrosion control practices. _ Section 2: Definitions(1) Alternating Current (AC): Current whose direction changes with time. Ampere: Unit of current that is one coulomb per second. Anode: The electrode of an electrochemical cell at which oxidation occ
29、urs. Electrons flow away from the anode in the external circuit. Corrosion usually occurs and metal ions enter the solution at the anode. Backfill: Material placed in a hole to fill the space around the anodes, vent pipe, and buried components of a cathodic protection system. Casing Potential Profil
30、e: Voltage (IR) drop and current direction versus casing depth is plotted. Amount of current is determined from the IR drop and casing resistance. (See nonmandatory Appendix A.) Casing-to-Electrolyte: See Structure-to-Electrolyte Po-tential. Casing-to-Reference Electrode: See Structure-to-Electrolyt
31、e Potential. Cathode: The electrode of an electrochemical cell at which reduction is the principal reaction. Electrons flow toward the cathode in the external circuit. Cathodic Protection: A technique to reduce the corrosion of a metal surface by making that surface the cathode of an electrochemical
32、 cell. Cement: Cement slurry fills the space between the casing and the sides of the wellbore to a predetermined height above the bottom of the well. Continuity Bond: A connection, usually metallic, that provides electrical continuity between structures that can conduct electricity. Corrosion: The d
33、eterioration of a material, usually a metal, that results from a reaction with its environment. Counterpoise: A conductor or system of conductors arranged beneath a power line, located on, above, or most frequently, below the surface of the earth and connected to the footings of the towers or poles
34、supporting the power line. Coupling (or Collar): Well casing joint connector. Current Density: The current to or from a unit area of an electrode surface. _ (1) Definitions in this section are those presented in the NACE Glossary of Corrosion-Related Terms and those that reflect the common usage amo
35、ng practicing corrosion control personnel. In many cases, in the interest of brevity and practicality, the strict scientific definitions are abbreviated or paraphrased. SP0186-2007 2 NACE International Deep Groundbed: One or more anodes installed vertically at a nominal depth of 15 m (50 ft) or more
36、 below the earths surface in a drilled hole for the purpose of supplying cathodic protection. Dielectric Coating: A coating that does not conduct electricity. Direct Current (DC): Current whose direction does not change with time. Drainage: Conduction of electric current from an underground or subme
37、rged metallic structure by means of a metallic conductor. E-log-I: A test that indicates the cathodic protection current required by a slope change on the cathodic polarization diagram. (Refer to nonmandatory Appendix B.) Electrical Isolation: The condition of being electrically separated from other
38、 metallic structures or the environment. Electric Log: A survey taken in the open borehole of a well to determine the lateral formation resistivity. Electrolyte: A chemical substance containing ions that migrate in an electric field. For the purposes of this standard, electrolyte refers to the soil
39、or liquid adjacent to and in contact with a buried or submerged metallic structure, including the moisture and other chemicals contained therein. Electroosmotic Effect: The effects of the movements in an electric field of liquid with respect to colloidal particles immobilized in a porous diaphragm o
40、r a single capillary tube. Fault Current: A current that flows from one conductor to ground or to another conductor due to an abnormal connection (including an arc) between the two. A fault current flowing to the ground may be called a ground fault current. Field: A group of wells in close physical
41、proximity, usually considered a unit when applying cathodic protection. It may be an oil or natural gas production field or a natural gas storage field. Foreign Structure: Any metallic structure that is not intended as a part of a system under cathodic protection. Galvanic Anode: A metal that provid
42、es sacrificial protection to another metal that is more noble when electrically coupled in an electrolyte. This type of anode is the electron source in one type of cathodic protection. Gamma Ray Neutron Log: Gamma ray is a measurement of the natural radioactivity of a formation. Neutron log is used
43、for delineation of porous formations. Data are used to identify the formations in the earth. Groundbed: One or more anodes installed below the earths surface for the purpose of supplying cathodic protection. Impressed Current: An electric current supplied by a device employing a power source that is
44、 external to the electrode system. (An example is direct current for cathodic protection.) Instant-Off Potential: The polarized half-cell potential of an electrode taken immediately after the cathodic protection current is stopped, which closely approximates the potential without IR drop (i.e., the
45、polarized potential) when the current was on. Interference Bond: An intentional metallic connection, between metallic systems in contact with a common electrolyte, designed to control electrical current interchange between the systems. Intermediate Casing: A string of casing set to protect a section
46、 of hole and to allow drilling to continue to a greater depth. Also called protection casing string. IR Drop: The voltage across a resistance in accordance with Ohms law. Isolation: See Electrical Isolation. Lithology: Rock formations traversed by well casing. Long-Line Current: Current through the
47、earth between an anodic and a cathodic area that returns along an underground metallic structure. Mutual Interference: An electrical DC interference on a well originating from within the cathodic protection system of several wells and structures, such as several DC power sources for a group of wells
48、. Native State Potential: The potential with zero groundbed current. Negative Return: A point of connection between the cathodic protection negative cable and the protected structure. Ohm: A resistance that passes one ampere of current when a one-volt potential is applied. Packaged Anode: An anode that, when supplied, is already surrounded by a selected conductive backfill material. Photovoltaic: Generation of an electromotive
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