CN-119177452-B - Cathode protection potential testing device for underground casing of oil field and use method

CN119177452BCN 119177452 BCN119177452 BCN 119177452BCN-119177452-B

Abstract

The invention discloses a cathode protection potential testing device of an oilfield underground sleeve and a using method thereof, comprising a testing cable, a probe fixing device and a potential testing meter, wherein the testing cable comprises an outer plastic layer, a shielding metal layer and an inner plastic layer from outside to inside, a potential cable core, a second potential cable core and a reference cable core are arranged in the inner plastic layer, the lower end of the testing cable penetrates through a cable through hole, a potential connecting terminal is connected with the lower end of the second potential cable core, a standby potential connecting terminal is connected with the lower end of the second potential cable core, the lower end of the reference cable core is also connected with a reference electrode, the outer plastic layer is used for insulating a stratum from the outer wall of the sleeve, and then the shielding metal layer is used for electromagnetic shielding to prevent stratum potential interference, and the potentials of the two cable core ends on the ground are equal to the potentials of the underground potential connecting terminal and the solid reference electrode, namely the protection potential and the natural potential of the sleeve at the underground position to be tested are directly detected on the ground.

Inventors

CHENG BIHAI
TIAN YUXIN
LIU GUANGSHENG
LI QIONGWEI
LI KAI
LI MINGXING
YANG HUILI
WANG XIAOYONG
GUO GANG
SUN YULAI

Assignees

中国石油天然气股份有限公司

Dates

Publication Date: 20260508
Application Date: 20230621

Claims (8)

1. A cathode protection potential testing device of an oil field underground casing is characterized by comprising a testing cable (1-2), a potential testing meter (1-5) and a probe fixing device (1-1) connected outside the casing (1-10), The probe fixing device (1-1) is a conical sleeve clamping tooth (3-1), the sleeve clamping tooth (3-1) is connected outside the sleeve (1-10), a cable through hole (3-2) for a test cable (1-2) to pass through is formed in the sleeve clamping tooth (3-1), a locking screw cap (3-3) is connected to the outer side of the sleeve clamping tooth (3-1), and an electric potential wiring terminal (1-12) and a standby electric potential wiring terminal (1-13) are connected to the locking screw cap (3-3); The test cable (1-2) comprises an outer plastic layer (2-1), a shielding metal layer (2-2) and an inner plastic layer (2-3) from outside to inside, a first potential cable core (2-4), a second potential cable core (2-5) and a reference cable core (2-6) are arranged in the inner plastic layer (2-3), the lower end of the test cable (1-2) penetrates through the cable through hole (3-2), the potential connecting terminal (1-12) is connected with the lower end of the first potential cable core (2-4), the standby potential connecting terminal (1-13) is connected with the lower end of the second potential cable core (2-5), the lower end of the reference cable core (2-6) is also connected with a reference electrode (1-11), and the reference electrode (1-11) is fixed outside the sleeve (1-10) through the reference cable core (2-6); the upper end of the reference cable core (2-6) is a reference electrode cable end (1-4), the upper ends of the first potential cable core (2-4) and the second potential cable core (2-5) are a first potential cable end (1-6) and a second potential cable end (1-14) respectively, and the first potential cable end (1-6), the second potential cable end (1-14) and the reference electrode cable end (1-4) are connected with the potential test meter (1-5).
2. The cathodic protection potential testing device of an oilfield downhole casing according to claim 1, further comprising a plurality of cable fixing devices (1-3), wherein the testing cables (1-2) are fixed on the outer side of the casing (1-10) through the cable fixing devices (1-3), and the cable fixing devices (1-3) are nylon ties or insulating tapes.
3. The cathodic protection potential testing device of an oilfield downhole casing according to claim 1, wherein the probe fixing device (1-1) is made of the same material as the casing (1-10).
4. The cathodic protection potential testing device of the underground casing of the oil field as claimed in claim 1, wherein the vertical distance between the probe of the reference electrode (1-11) and the outer wall of the casing (1-10) is within 18 mm.
5. The cathodic protection potential testing device of an oilfield downhole casing according to claim 1, wherein the first potential cable core (2-4), the second potential cable core (2-5) and the reference cable core (2-6) are dual-core aluminum or copper metals with the same wire diameter and the same material property.
6. The cathodic protection potential testing device of an oilfield downhole casing according to claim 5, wherein the first potential cable core (2-4), the second potential cable core (2-5) and the reference cable core (2-6) are respectively sleeved with a plastic layer, and the first potential cable core (2-4) and the reference cable core (2-6) are in a twisted pair winding structure.
7. The method of using a cathodic protection potential testing apparatus for a casing in an oilfield well according to any one of claims 1-6, comprising the steps of: Before the sleeve (1-10) is put in, connecting the probe fixing device (1-1) to the outer side of the sleeve (1-10), enabling the lower end of the test cable (1-2) to penetrate out of the cable through hole (3-2), connecting the reference electrode (1-11) with the reference cable core (2-6) at the lower end of the test cable (1-2), connecting the potential connecting terminal (1-12) and the standby potential connecting terminal (1-13) to the locking wire cap (3-3), and connecting the other ends of the potential connecting terminal (1-12) and the standby potential connecting terminal (1-13) with the first potential cable core (2-4) and the second potential cable core (2-5) respectively; The method comprises the steps of (1) setting a sleeve (1-10), setting test cables (1-2) synchronously along the sleeve (1-10) when setting the sleeve (1-10), and fixing the test cables (1-2) on the sleeve (1-10) through cable fixing devices (1-3) at certain intervals in the setting process; After the sleeve (1-10) is put into, connecting a reference electrode cable end (1-4), a first potential cable end (1-6) and a second potential cable end (1-14) of a test cable (1-2) left on the ground with a potential test meter (1-5), and connecting a shielding metal layer (2-2) of the test cable (1-2) with a grounding end of the potential test meter (1-5); The potential between the reference electrode cable end (1-4) and the first potential cable end (1-6) is measured when the sleeve (1-10) does not pass the cathodic protection current, the potential is the natural corrosion potential of the sleeve position at the corresponding depth in the unprotected state, and then the potential between the reference electrode cable end (1-4) and the first potential cable end (1-6) is measured when the cathodic protection current is conducted, and the potential is the protection potential.
8. The method for using the cathodic protection potential testing device for the underground casing of the oil field, which is disclosed in claim 7, is characterized in that a plurality of probe fixing devices (1-1) positioned at different depths are connected to the outer side of the casing (1-10), each probe fixing device (1-1) is connected with an overground potential testing meter (1-5) through a testing cable (1-2), and natural corrosion potential and protection potential at different depths of the underground casing (1-10) are measured.

Description

Cathode protection potential testing device for underground casing of oil field and use method Technical Field The invention belongs to the field of corrosion detection, and particularly relates to a cathode protection potential testing device for an oilfield downhole casing and a use method thereof. Background The oil-water well of the oil field of all countries of the world is widely applied to the production of the well cementation and completion of the sleeve, and the underground water of the stratum causes non-negligible external corrosion damage to the sleeve. In order to protect the integrity of the casing string to ensure long-term safe service of the oil-water well, oil-gas manufacturers generally adopt a casing impressed current cathodic protection technology which has been applied to the oil field for centuries and has remarkable effects. In the aspect of cathode protection effect evaluation, the cathode protection criteria specified by national standards GB/T21447-2018, steel pipeline external corrosion control Specification, GB/T21448-2017, buried steel pipeline cathode protection technical Specification, GB/T33791-2017, steel well casing cathode protection corrosion resistant operation Specification and the like are that the protection potential of metal is negatively shifted by 100mV, or 850mV is reached after IR drop is removed, the measurement method adopts a near-field method or a far-field method, and the specific operation is that a reference electrode is buried near a measurement point or at a relatively far position without electric field interference, and the potential difference value between the reference electrode and a position point is an absolute potential value. For a vertical pipeline, namely an oil-water well casing, because a cement sealing stratum is adopted outside the oil-water well casing, a reference electrode cannot be directly lowered into an annular space between the casing and the stratum, at present, the cathodic protection potential of the outer wall of the casing at the deep well is not directly measured, and is usually calculated and detected indirectly through numerical simulation calculation or a downhole potential profile logging instrument or an E-LogI method to evaluate whether the cathodic protection effect reaches the standard or not, and the method is recommended as a national standard method in GB/T33791-2017 technical Specification for cathode protection corrosion protection of steel well casings. The literature "well casing underground cathodic protection potential calculation method research" (Chinese corrosion and protection journal, 12 months 2001, 21 st volume, 6 th period) provides a method for calculating the cathodic protection potential of a certain depth position of an underground casing by detecting a protection parameter on the ground and according to a basic well completion parameter of the casing, wherein a calculation model is complex, and the method belongs to indirect measurement of theoretical calculation type. The document "cased well potential profile logging instrument" (logging technique, 2002, 26 th and 4 th) proposes to detect the potential by using a downhole potential profile logging instrument, the instrument has 2 elastic contact arm probes which are less than 10m apart, under the condition of passing a protection current, the potential difference between the two probes is detected downhole, whether the cathodic protection meets the protection standard (namely, eliminating the anode region) is calculated by using the potential difference, and the technology cannot detect the cathodic protection potential and still belongs to the calculation of indirect measurement effect. The direct potential measurement is a basic means for evaluating the cathodic protection effect of a ground pipeline, and the current evaluation of the cathodic protection effect of the oil field casing is only indirectly evaluated because of the limitation of the well structure, so that the direct potential measurement is sought to be the target pursued by corrosion workers and is also a realistic requirement for production. Disclosure of Invention The invention aims to provide a cathode protection potential testing device for an oilfield downhole casing and a use method thereof, so as to directly evaluate the cathode protection effect of the oilfield casing. The invention aims at realizing the following technical means, a cathode protection potential testing device of an oil field underground casing, which comprises a testing cable, a potential testing meter and a probe fixing device connected outside the casing, The probe fixing device is a conical sleeve clamping tooth, the sleeve clamping tooth is connected outside the sleeve, a cable through hole for a test cable to pass through is further formed in the sleeve clamping tooth, a locking wire cap is connected to the outer side of the sleeve clamping tooth, and a potential binding post and a standby pote