CN110408939B - Method for determining internal corrosion-resistant anode protection interval of coating well in casing - Google Patents

Method for determining internal corrosion-resistant anode protection interval of coating well in casing Download PDF

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CN110408939B
CN110408939B CN201910603601.4A CN201910603601A CN110408939B CN 110408939 B CN110408939 B CN 110408939B CN 201910603601 A CN201910603601 A CN 201910603601A CN 110408939 B CN110408939 B CN 110408939B
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mineralization
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coating
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程碧海
杨立华
戚建晶
刘汉斌
付彩利
卢文伟
刘彬
霍征光
陈彦云
刘曼
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Petrochina Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/005—Anodic protection
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
    • C23F2213/30—Anodic or cathodic protection specially adapted for a specific object
    • C23F2213/32—Pipes

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Abstract

The invention discloses a method for determining the internal corrosion-resistant anode protection interval of a casing internal coating well, which determines the installation mode of a casing built-in sacrificial anode by combining the means of an indoor simulation experiment according to the distribution of the internal corrosion-resistant anodes of different well depths, different well fluid mineralization degrees and different internal coating integrity rates, thereby avoiding the technical complexity of field experiments, reducing the period and the times of the indoor experiment, and avoiding the repeated experiments of each oil well to determine the anode distribution parameters due to different fluid media and the internal coating integrity rates of the casing. The invention has the advantages of quick and easy experiment, reliable technology and good economical efficiency.

Description

Method for determining internal corrosion-resistant anode protection interval of coating well in casing
Technical Field
The invention relates to the field of corrosion and protection of oil fields, in particular to a method for determining an internal corrosion prevention anode protection interval of a coating well in a casing.
Background
At present, oil well pipe columns of oil field production enterprises generally adopt common carbon steel pipes, and oil well produced liquid seriously corrodes carbon steel sleeves. In order to safely and efficiently develop oil fields, various casing anticorrosion measures except for a pipe are generally adopted in each oil field, such as external current cathodic protection external anticorrosion with early application and mature technology, epoxy cold winding belt (epoxy coating) sacrificial anode anticorrosion widely applied in China, commonly-implemented corrosion inhibitor filling technology and the like.
The patent "a sacrificial anode protection device for inner coating cased well (CN 105154889B)" discloses a sacrificial anode device for corrosion prevention inside casing by using oil pipe to carry sacrificial anode, and does not further describe how the sacrificial anode on the oil pipe should be distributed; the patent "a downhole evaluation device for sacrificial anode material" (CN105401921B) discloses a device for downhole evaluation of the working condition of anodes, but does not provide a downhole distribution of the anodes; the document "a tool development for preventing corrosion of casing pipe with the oil pipe going into well" (xiaozhiying, li jonwei, order forever, etc., oil industry technical supervision, vol.33no.3mar.2017) describes the field application condition and effect of the anticorrosion anode in the casing pipe, and does not relate to the anode protection potential or installation mode; the patent "oil well casing cathode protection system and electrode placement method based on pulse current" (CN104562043B) "discloses a potential distribution detection method of casing impressed current cathode protection, which is to detect the distribution potential at different positions of the casing outer wall by wrapping and binding a reference electrode cloth on the casing outer wall through a heat insulating material. The prior patent documents do not discuss an anode installation and arrangement method of the sacrificial anode in the sleeve, the distribution and installation of the sacrificial anode in the sleeve cannot be determined in production, and the installation and arrangement of the sacrificial anode are mainly determined according to the design experience of the electrochemical parameters of the anode in a ground pipeline and a storage tank.
Because the electromagnetic action range of the sacrificial anode in the limited space of the oil well casing is limited, the oil well casing is more than kilometer in underground depth, the protective potential of the sacrificial anode in the casing is naturally difficult to measure, the method for detecting the distribution potential of the outer wall of the casing is feasible by adopting the principle that a reference electrode is fixed on the oil pipe to measure the potentials at different positions of the inner wall of the casing, the direct detection is almost impossible due to great difficulty in realizing, and the reasonable distribution of the sacrificial anode in the casing can not be known from verification, so that the distribution of the anode can not be reasonably determined; if the protection potential and the distance distribution of the sacrificial anode in any shaft environment are simulated and tested indoors, the workload is too large, and the time, the labor and the cost are high. Therefore, the technology of preventing the sleeve from being corroded by the sacrificial anode is scientifically and reasonably adopted, scientific protection of the sleeve by the sacrificial anode is realized, the cathode protection criterion specified by the national standard is met, underprotection or over-protection is prevented, the distribution method of the sacrificial anode in the sleeve under the corrosion environment with different temperatures, mineralization degrees and coating integrity rates must be mastered, the installation mode of the sacrificial anode in the longitudinal direction in the sleeve is determined, and the production problem of reasonable application of the sacrificial anode which troubles the corrosion prevention in the sleeve is solved.
Disclosure of Invention
The invention aims to overcome the defects and provides a method for determining the protection interval of an internal anticorrosion anode of a coating well in a casing, which can master the distribution of sacrificial anodes in the casing under the corrosion environments with different temperatures, mineralization degrees and coating integrity rates so as to determine the installation mode of the sacrificial anodes in the casing in the longitudinal direction and solve the production problem of the reasonable application of the sacrificial anodes disturbing the corrosion prevention in the casing.
In order to achieve the above object, the present invention comprises the steps of:
s101, obtaining a relational expression of the protection length and the protection potential of the sleeve anode in a corrosion environment with certain temperature, mineralization and internal coating integrity through experiments;
s102, determining the temperature, the mineralization degree and the gradient value of the coating integrity rate of the protection length;
s103, establishing a relational expression of protection length, temperature, mineralization degree and coating integrity;
s104, establishing a relational expression of the mineralization degree and the temperature under the known coating completeness rate and the series protection length;
s105, drawing a graph of a relation curve between the mineralization and the well depth under the conditions of known coating completeness and series protection lengths;
s106, changing the known coating completeness, and repeatedly drawing to form a curve group diagram of the relation between the mineralization and the well depth under the series of protection lengths;
s107, detecting the completeness of the underground casing coating and the mineralization degree of well fluid, and looking up or detecting the geothermal gradient;
and S108, obtaining a protection interval through a relation curve set according to the known sleeve coating completeness, the well fluid mineralization and the well depth.
In S101, the relation between the protection length and the protection potential includes a four-term relation equation obtained by experiments in four environments, where the four environments are the reference temperature TBase ofReference degree of mineralization MBase ofReference coating integrity ratio CBase ofHigh temperature THeight ofReference degree of mineralization MBase ofReference coating integrity ratio CBase ofReference temperature TBase ofHigh degree of mineralization MHeight ofReference coating integrity ratio CBase ofAnd a reference temperature TBase ofReference degree of mineralization MBase ofHigh coating integrity CHeight ofEnvironment, the corresponding relational equation is the reference temperature reference mineralization degree reference coating integrity equation TBase ofMBase ofCBase ofEquation, high temperature reference salinity reference coating integrity equation THeight ofMBase ofCBase ofEquation, reference temperature hypersalinity equation reference coating integrity equation TBase ofMHeight ofCBase ofEquation and reference temperature reference mineralization high coating integrity equation TBase ofMBase ofCHeight ofAnd (4) an equation.
High temperature and hypersalinity can be replaced by low temperature and hypomineralisation.
In S102, the temperature gradient L of the guard length/ΔTReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and high temperature baseline salinity baseline coating integrity THeight ofMBase ofCBase ofThe equation is determined:
L/ΔT＝ΔL/ΔT＝(Lt radical－LHeight of T)/(THeight of－TBase of)
Mineralization gradient value L of protection length/ΔMReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and reference temperature hypersalinity equation reference coating integrity rate TBase ofMHeight ofCBase ofThe equation is determined:
L/ΔM＝ΔL/ΔM＝(Lm is high－LM radical)/(MHeight of－MBase of)
Coating integrity gradient value L of protection length/ΔCReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and reference temperature reference mineralization high coating integrity rate TBase ofMBase ofCHeight ofThe equation is determined:
L/ΔC＝ΔL/ΔC＝(Lheight of C－LC radical)/(CHeight of－CBase of)。
In S103, the relationship among the protection length, the temperature, the mineralization and the coating integrity is as follows:
L＝Lbase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(C－CBase of)×L/ΔC
Wherein L isBase ofReference coating integrity for reference temperature reference salinityBase ofMBase ofCBase ofThe value of the equation, L is the protection length, C is the coating integrity, M is the degree of mineralization and T is the temperature.
In S104, the relationship between the degree of mineralization under the known coating integrity and the series of protection lengths and the temperature is as follows:
Li＝Lbase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
Wherein, CIt is known thatFor known coating integrity, LiT is the degree of mineralization at the length of the series of protections and T is the temperature.
In S101, the mineralization degree of the anode of the sleeve under a corrosive environment is 10-100 g/l, the temperature is less than 80 ℃, the completeness rate of the coating is 0-100%, the reference temperature and the reference mineralization degree are intermediate values of the actual application environment temperature and the mineralization degree range, the completeness rate of the reference coating is 0-50%, the temperature and mineralization degree range is required to be within 50% of the intermediate value, and if the mineralization degree exceeds +/-50% of the intermediate value, an encryption simulation test is required.
Compared with the prior art, the method determines the installation mode of the sacrificial anode arranged in the casing by combining the means of indoor simulation experiments according to the distribution of the anode for corrosion prevention in the casing with different well depths, different well fluid mineralization degrees and different internal coating integrity rates, avoids the technical complexity of field experiments, reduces the period and the times of the indoor experiments, and avoids the repeated experiments for each oil well to determine the anode distribution parameters due to different fluid media and the internal coating integrity rates of the casing. The invention has the advantages of quick and easy experiment, reliable technology and good economical efficiency.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 shows a certain coating integrity ratio M1A curve graph of the relation between the well depth and the mineralization degree when the protection length is equal to 5 m;
FIG. 3 shows a certain coating integrity ratio M1A graph of the relationship between the well depth and the mineralization degree when the protection length is equal to 10 m;
FIG. 4 is a template of the internal corrosion protection anode protection distance when the coating integrity rate in the casing is 30%;
FIG. 5 is a template of internal anticorrosion anode protection space when the coating integrity in the casing is 50%;
FIG. 6 is a template of internal corrosion protection anode protection distance when the integrity of the coating in the casing is 70%;
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the anode installation mode is determined according to the anode distribution of the corrosion prevention in the casing pipe with different well depths, different well fluid mineralization degrees and different internal coating integrity rates according to the following steps:
the first step is as follows: the method comprises the steps of obtaining the relation between the protection length and the protection potential of the casing under the corrosion environment with certain temperature, mineralization and internal coating integrity rate through experiments, namely an L-U relational expression, comprising a four-term relational expression equation obtained through experiments under four environments, wherein the four environments are respectively reference temperature (T)Base of) Degree of reference mineralization (M)Base of) Reference coating integrity ratio (C)Base of) High temperature (T)Height of) Degree of reference mineralization (M)Base of) Reference coating integrity ratio (C)Base of) Reference temperature (T)Base of) Height ofDegree of mineralization (M)Height of) Reference coating integrity ratio (C)Base of) And a reference temperature (T)Base of) Degree of reference mineralization (M)Base of) High coating integrity (C)Height of) Environment, corresponding relational equation is reference temperature reference mineralization degree reference coating integrity equation (T)Base ofMBase ofCBase ofEquation), high temperature baseline salinity baseline coating integrity equation (T)Height ofMBase ofCBase ofEquation), reference temperature hypersalinity equation reference coating integrity equation (T)Base ofMHeight ofCBase ofEquation) and a reference temperature reference mineralization high coating integrity equation (T)Base ofMBase ofCHeight ofAn equation).
The mineralization value of a corrosive environment is 10-100 g/l, the temperature is less than 80 ℃, the coating integrity is 0-100%, the reference temperature and the reference mineralization are intermediate values of the actual application environment temperature and the mineralization range, the reference coating integrity can be 0-50%, the temperature and mineralization range is required to be within 50% of the intermediate value, and if the mineralization value exceeds +/-50% of the intermediate value, an encryption simulation test is required.
The high temperature and high mineralization degree in four corrosive environments can also be low temperature and low mineralization degree.
The corrosion medium of the simulation experiment is taken from the stratum water fluid medium of the actual oil well shaft, and the medium flow rate is the same as that of the field.
The protection potential U is determined by two methods, according to the protection criteria established by the standard specifications of metal structures: firstly, a fixed value of-0.85V is taken, and secondly, the protection potential offset delta U is determined according to the negative offset of 100mV, wherein U is equal to UNature of natureΔ U, U being the protective potential, UNature of natureThe corrosion potential is the natural corrosion potential of the sleeve material without adding the sacrificial anode, and the delta U is the offset of the protection potential determined by experiments.
The protection length L is the maximum distance of the single side of the sleeve protected by the sacrificial anode.
The anticorrosive sacrificial anode in the sleeve is arranged in the sleeve through the oil pipe, the metal elastic contact arm is electrically and mechanically connected with the inner wall of the sleeve, and meanwhile, the sacrificial anode and the oil pipe body are electrically insulated through plastic.
The simulation experiment time is the time when the stable polarization of the sleeve is achieved, namely the shortest time when the potential is not stabilized along with the change of the time.
The four-environment experiment is the minimum number of simulation experiments but is not limited to the simulation experiments, and the corrosion environment can be increased.
The second step is that: according to TBase ofMBase ofCBase ofEquation and THeight ofMBase ofCBase ofEquation determination of temperature gradient value L of protection length/ΔT(unit: m/. degree. C.):
L/ΔT＝ΔL/ΔT＝(Lt radical－LHeight of T)/(THeight of－TBase of)
According to L/delta T TBase ofMBase ofCBase ofEquation and TBase ofMHeight ofCBase ofDetermination of mineralization gradient value L of lower protection length by equation/ΔM[ unit: m/(g/l)]：
L/ΔM＝ΔL/ΔM＝(LM is high－LM radical)/(MHeight of－MBase of)
According to TBase ofMBase ofCBase ofEquation and TBase ofMBase ofCHeight ofEquation determination of coating integrity gradient value L for protection length/ΔC[ unit: m/(1/100)]：
L/ΔC＝ΔL/ΔC＝(LHeight of C－LC radical)/(CHeight of－CBase of)
The third step: and establishing a relational expression of the protection length L, the coating integrity C, the mineralization M and the temperature T (T has a corresponding relation with the well depth H).
L＝LBase of-(T－TBase of)×L/ΔT+(M－MBase of)×L/ΔM+(C－CBase of)×L/ΔC
In the formula, LBase ofIs TBase ofMBase ofCBase ofThe value of the equation, i.e. the three factors TBase ofMBase ofCBase ofDetermination of the protective length L obtained by experimentsBase of。
The fourth step: establishing a known coating integrity CIt is known thatProtection length of seriesLiThe degree of mineralization M at the following point is related to the temperature T.
Li＝LBase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
The fifth step: and (4) drawing a graph of the mineralization degree and temperature relation curve under the known coating completeness and series protection lengths.
L1＝LBase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
L2＝LBase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
……
Li＝LBase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
……
Ln＝LBase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
LiEqual to 5, 10, 15, 20, 30, respectively.
Further, from the linear relationship between the well depth H and the temperature T, the mineralization degree-temperature curve set is converted into a mineralization degree-well depth curve set, as shown in fig. 2 and fig. 3.
And a sixth step: changing the known coating completeness, and repeatedly drawing a curve group diagram (see a template diagram) of the mineralization degree and the well depth under the condition of forming a series of protection lengths.
And combining well depth-mineralization degree curves of different protection lengths under the same coating integrity rate in the same graph to obtain a protection length template under the coating integrity rate.
The seventh step: and detecting the completeness of the coating of the downhole casing of the oil well and the mineralization degree of produced liquid, looking up the ground temperature gradient, and also directly detecting the temperature of the well fluid.
Eighth step: and obtaining the anode protection length under the well environment, namely the protection distance (the value of which is equal to 2 times of the protection length) by drawing a relation curve set (template) according to the known sleeve coating completeness and the production fluid mineralization.
And finding out the corresponding protection length from the template graph according to the detected parameters of the underground casing coating completeness, the well fluid mineralization and the well depth, namely the temperature.
Example 1:
the pit shaft temperature of the oil well with the anode to be subjected to corrosion prevention in the casing in a certain area is about 25-55 ℃, the mineralization degree of formation water is about 70-30 g/l, the casing of the well with the anode in the area is subjected to internal corrosion prevention by adopting the sacrificial anode, the reasonable distribution of the sacrificial anode in the casing needs to be mastered, and the method comprises the following steps:
the first step is as follows: the method comprises the steps of obtaining the relation between the protection length and the protection potential of the sleeve material in a corrosion environment with certain temperature, mineralization and internal coating integrity rate through experiments, namely an L-U relational expression, comprising a four-term relational expression equation obtained through experiments in four environments, wherein the four environments are respectively reference temperature (T)Base ofStandard degree of mineralization (M) 28 ℃Base of12g/l) benchmark coating integrity (C)Base of0, no coating), high temperature (T)Height ofStandard degree of mineralization (M) 60 ℃Base of) Reference coating integrity ratio (C)Base of) Reference temperature (T)Base of) High degree of mineralization (M)Height of78g/l) reference coating integrity (C)Base of) And a reference temperature (T)Base of) Degree of reference mineralization (M)Base of) High coating integrity (C)Height of100%) environment, the corresponding equation of the relationship is the reference temperature reference degree of mineralization reference coating integrity (T) respectivelyBase ofMBase ofCBase ofEquation), high temperature baseline salinity baseline coating integrity equation (T)Height ofMBase ofCBase ofEquation), reference temperature hypersalinity equation reference coating integrity (T)Base ofMHeight ofCBase ofEquation) and reference temperature reference mineralization high coating integrity (T)Base ofMBase ofCHeight ofAn equation).
1. 12g/l +28 ℃ C. + without coatingT in layer "environmentBase ofMBase ofCBase ofThe equation:
L＝49.7U2+102U+52.5
2. t in the environment of 12g/l +60 ℃ plus no coatingHeight ofMBase ofCBase ofThe equation:
L＝24.3U2+51.2U+27
3. t in the environment of 78g/l +28 ℃ plus no coatingBase ofMHeight ofCBase ofThe equation:
L＝188.7U2+369.5U+181.2
4. t in an environment of "12 g/l +28 ℃ C. + coating integrity 100%Base ofMBase ofCHeight ofThe equation:
L＝60.2U+63.6
the second step is that: determining gradient values of the influencing factors.
1. According to TBase ofMBase ofCBase ofEquation and THeight ofMBase ofCBase ofEquation determination of temperature gradient value L of protection length/ΔT(unit: m/. degree. C.):
L/ΔT＝ΔL/ΔT＝(Lt radical－LHeight of T)/(THeight of－TBase of)
Under "12 g/l +60 ℃ + no coating" and "12 g/l +28 ℃ + no coating", the protection lengths were 2.9m and 6.5m, respectively, and the calculated protection lengths decreasing for each 1 ℃ increase, with the degree of mineralization, coating unchanged, were:
L/ΔT＝(6.5-2.9)/(60-28)＝0.113m/℃
2. according to TBase ofMBase ofCBase ofEquation and TBase ofMHeight ofCBase ofEquation determination of mineralization gradient value L of guard length/ΔM[ unit: m/(g/l)]：
L/ΔM＝ΔL/ΔM＝(LM is high－LM radical)/(MHeight of－MBase of)
Under "78 g/l +28 ℃ + uncoated" and "12 g/l +28 ℃ + uncoated", the protection lengths at the determined effective protection potentials were 14m and 9.6m, respectively, and the increase in protection length per 1g/l increase at constant temperature, coating integrity rate was calculated as:
L/ΔM＝(14-9.6)/(78-12)＝0.067m/(g/l)
3. according to TBase ofMBase ofCBase ofEquation and TBase ofMBase ofCHeight ofEquation determination of coating integrity gradient value L for protection length/ΔC[ unit: m/(1/100)]：
L/ΔC＝ΔL/ΔC＝(LHeight of C－LC radical)/(CHeight of－CBase of)
Under "12 g/l +28 ℃ + coating integrity 100%" and "12 g/l +28 ℃ + no coating", the protection lengths were 22.1m and 9.6m, respectively, and the increase in protection length per 1% increase in coating integrity was calculated at a constant degree of mineralization, temperature:
L/ΔC(22.1-9.6) × 100/(100-0) ═ 12.5 m/perfection factor
The third step: and establishing a relational expression of the protection length L, the coating integrity C, the mineralization M and the temperature T (T has a corresponding relation with the well depth H).
Substituting the known value into the formula:
L＝Lbase of-(T－TBase of)×L/ΔT+(M－MBase of)×L/ΔM+(C－CBase of)×L/ΔC
L＝9.6-(T-28)×0.188+(M-12)×0.067+(C－0)×12.5
＝0.067M-0.188T+12.5C+14.06
The fourth step: establishing a known coating integrity CIt is known thatProtection length L of seriesiThe degree of mineralization M at the following point is related to the temperature T.
According to the formula L-0.067M-0.188T +12.5C +14.06
Taking the known sleeve coating integrity rate as 30%, and substituting the known sleeve coating integrity rate into the formula to obtain:
L＝0.067M-0.188T+12.5C+14.06
＝0.067M-0.188T+17.81
taking the earth temperature gradient of 0.027 ℃/M, converting the temperature into the well depth H, T/0.027, and establishing an anode protection spacing relation formula of the mineralization degree M and the well depth H:
L＝0.067M-0.005076H+17.81 (1)
different protection intervals Li(5, 10, 15 and 20M) are substituted into the formula (1) to obtain a relational expression of the mineralization degree M and the well depth H, and a protection interval template can be established by drawing a relational graph under different intervals, which is shown in tables 1, 2 and 2.
TABLE 1 data table of the relationship between mineralization and well depth under different protection lengths when the coating integrity in the casing is 30%
Figure GDA0003216302580000071
TABLE 2 corresponding well depth data for different mineralization degrees and different protection intervals at 30% of coating integrity in casing
Figure GDA0003216302580000072
Figure GDA0003216302580000081
The fifth step: and drawing a graph of the mineralization M and the temperature T under the conditions of the known coating integrity C and the series protection length L.
Will be M of Table 2i－HiThe data set is plotted to obtain a protection distance template of the internal corrosion-resistant anode when the coating integrity rate in the sleeve is 30 percent, and the protection distance template is shown in figure 4.
And a sixth step: changing the known coating completeness, and repeatedly drawing a curve group diagram of the mineralization degree and the well depth under the condition of serial protection lengths.
And combining well depth-mineralization degree curves of different protection lengths under the same coating integrity rate in the same graph to obtain a protection length template under the coating integrity rate.
And (3) taking the known integrity of the inner coating to be 50% and 70%, repeating the fourth step to the sixth step to respectively obtain the templates with the internal anticorrosion anode protection spacing when the integrity of the inner coating of the sleeve is 50% and 70%, as shown in figures 5 and 6 (the mineralization is only used for reference in the range of 150-200 g/l).
The seventh step: the method can detect the completeness of the underground casing coating and the mineralization degree of produced liquid, look up the ground temperature gradient and also directly detect the temperature of the well liquid.
The well depth of a certain well is 1800m, the mineralization degree of the detected well fluid is 25g/l, the integrity of the inner coating is 25%, and the distribution distance of the anticorrosion anodes in the well needs to be determined.
Eighth step: and obtaining the anode protection length under the well environment, namely the protection distance through a relation curve chart (template) according to the known sleeve coating completeness and the mineralization degree of the produced liquid.
By using a plate with an internal coating integrity of 30%, the distribution distance of the anodes is 20m according to the mineralization-well depth data corresponding to the horizontal and vertical coordinates from fig. 4.
The invention calculates the conclusion according to the theoretical research and software of the sacrificial anode in the sleeve, the protective distance of the sacrificial anode to the inner wall of the sleeve is in proportional linear relation with the temperature, the mineralization and the coating integrity of the fluid medium in the sleeve, in order to determine the protective distance of the sacrificial anode in the environments with different temperatures, mineralization and coating integrity, the invention selects limited temperature nodes, mineralization nodes and coating integrity nodes to carry out indoor simulation experiment, determines the protective potential data set on different sleeve positions under the influence of single factor (factor refers to temperature, mineralization or coating integrity) when the sacrificial anode works under the environment of each node, so as to fit the relation equation of the protective length and the protective potential of each influencing factor, and then obtains the protective length gradient under the influence of the single temperature, mineralization and coating integrity factor according to the calculation, because of the temperature, the mineralization and the coating integrity, The influence of the mineralization and the coating integrity on the conductivity of the medium is in a linear relation, and further a relation equation of the protection length of the shaft fluid medium environment in a corrosion environment of any temperature, any mineralization and coating integrity medium environment and three factors of the temperature, the mineralization and the coating integrity is obtained. Finally, fixing two factors of protection length and coating integrity respectively, and transforming to obtain two factor relation equations of temperature and mineralization degree under a certain coating integrity and a certain series of protection lengths, so that the equations draw a series relation curve of the two factors on the same coordinate graph, and one coordinate graph represents a distribution template of the anode under different temperature and mineralization degree under the condition of coating integrity. After the sleeve coating integrity and the well fluid mineralization of a certain well are measured, the protection length of the anode can be determined according to the well depth (the well depth actually corresponds to the temperature), namely the distribution distance is determined.

Claims (4)

1. A method for determining the internal corrosion prevention anode protection distance of a coating well in a casing is characterized by comprising the following steps:
s101, obtaining a relational expression of the protection length and the protection potential of the sleeve anode in a corrosion environment with certain temperature, mineralization and internal coating integrity through experiments;
s102, determining the temperature, the mineralization degree and the gradient value of the coating integrity rate of the protection length;
s103, establishing a relational expression of protection length, temperature, mineralization degree and coating integrity;
s104, establishing a relational expression of the mineralization degree and the temperature under the known coating completeness rate and the series protection length;
s105, drawing a graph of a relation curve between the mineralization and the well depth under the conditions of known coating completeness and series protection lengths;
s106, changing the known coating completeness, and repeatedly drawing to form a curve group diagram of the relation between the mineralization and the well depth under the series of protection lengths;
s107, detecting the completeness of the underground casing coating and the mineralization degree of well fluid, and looking up or detecting the geothermal gradient;
s108, obtaining a protection interval through a relation curve set diagram according to the known sleeve coating completeness, the well fluid mineralization and the well depth;
in S102, the temperature gradient L of the guard length/ΔTReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and high temperature baseline salinity baseline coating integrity THeight ofMBase ofCBase ofThe equation is determined:
L/ΔT＝ΔL/ΔT＝(Lt radical－LHeight of T)/(THeight of－TBase of)
Mineralization gradient value L of protection length/ΔMReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and reference temperature hypersalinity equation reference coating integrity rate TBase ofMHeight ofCBase ofThe equation is determined:
L/ΔM＝ΔL/ΔM＝(Lm is high－LM radical)/(MHeight of－MBase of)
Coating integrity gradient value L of protection length/ΔCReference coating integrity rate T according to reference temperature reference mineralization degreeBase ofMBase ofCBase ofEquation and reference temperature reference mineralization high coating integrity rate TBase ofMBase ofCHeight ofThe equation is determined:
L/ΔC＝ΔL/ΔC＝(Lheight of C－LC radical)/(CHeight of－CBase of)；
In S103, the relationship among the protection length, the temperature, the mineralization and the coating integrity is as follows:
L＝Lbase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(C－CBase of)×L/ΔC
Wherein L isBase ofReference coating integrity for reference temperature reference salinityBase ofMBase ofCBase ofThe value of the equation, L is the protection length, C is the coating integrity, M is the degree of mineralization and T is the temperature;
in S104, the relationship between the degree of mineralization under the known coating integrity and the series of protection lengths and the temperature is as follows:
Li＝Lbase of-(T－TBase of)×L/ΔT+(M-MBase of)×L/ΔM+(CIt is known that－CBase of)×L/ΔC
Wherein, CIt is known thatFor known coating integrity, LiFor the series protection length, T is the temperature.
2. The method for determining the distance between the anode and the cathode for anticorrosion of the coating well in the casing according to claim 1,in S101, the relation between the protection length and the protection potential includes a four-term relation equation obtained by experiments in four environments, where the four environments are the reference temperature TBase ofReference degree of mineralization MBase ofReference coating integrity ratio CBase ofHigh temperature THeight ofReference degree of mineralization MBase ofReference coating integrity ratio CBase ofReference temperature TBase ofHigh degree of mineralization MHeight ofReference coating integrity ratio CBase ofAnd a reference temperature TBase ofReference degree of mineralization MBase ofHigh coating integrity CHeight ofEnvironment, the corresponding relational equation is the reference temperature reference mineralization degree reference coating integrity equation TBase ofMBase ofCBase ofEquation, high temperature reference salinity reference coating integrity equation THeight ofMBase ofCBase ofEquation, reference temperature hypersalinity reference coating integrity equation TBase ofMHeight ofCBase ofEquation and reference temperature reference mineralization high coating integrity equation TBase ofMBase ofCHeight ofAnd (4) an equation.
3. The method for determining the distance between the anode protection and the corrosion protection of the coated well in the casing according to claim 2, wherein the high temperature and the high salinity can be replaced by the low temperature and the low salinity.
4. The method for determining the internal corrosion prevention anode protection interval of the coating well in the casing according to claim 1, wherein in S101, the mineralization degree of the casing anode in a corrosion environment is 10-100 g/l, the temperature is less than 80 ℃, the coating integrity is 0-100%, the reference temperature and the reference mineralization degree are intermediate values of the actual application environment temperature and the mineralization degree range, the reference coating integrity is 0-50%, the temperature and mineralization degree range is required to be within 50% of the intermediate values, and if the temperature and mineralization degree range exceeds +/-50% of the intermediate values, an encryption simulation test is required.
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JP2012097315A (en) * 2010-11-01 2012-05-24 Ps Mitsubishi Construction Co Ltd Method for installing anode material for electrolytic protection to reinforced concrete structure
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