CN112430782A

CN112430782A - Casing for geothermal well and manufacturing method thereof

Info

Publication number: CN112430782A
Application number: CN202011148621.6A
Authority: CN
Inventors: 王蕊; 李东风; 施宜君; 韩军; 杨鹏; 张益铭
Original assignee: China National Petroleum Corp; Pipeline Research Institute of CNPC
Current assignee: China National Petroleum Corp; Pipeline Research Institute of CNPC
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2021-03-02
Anticipated expiration: 2040-10-23
Also published as: CN112430782B

Abstract

The invention discloses a casing for a geothermal well and a manufacturing method thereof, belonging to the technical field of low alloy steel manufacturing. The strength is ensured by controlling the content of C, the high-temperature and corrosion resistance of the pipe is improved, the corrosion resistance is better when the content of P, S is lower, the interatomic binding force is improved by adjusting the content of Cr, Mo, W and Nb elements, the activation energy is increased by solid solution strengthening, a stable second phase is formed, the thermal stability of the material is improved, and meanwhile, the material has certain corrosion resistance; si, Al and other elements can form a compact oxide structure, and the grain size can be controlled. The performance indexes of the obtained steel pipe are as follows: the yield strength is more than 552MPa, the tensile strength is more than 655MPa, and the Charpy impact energy of the V-shaped notch sample is more than 30J; the average corrosion rate is less than 0.2 mm/a. Therefore, the geothermal well casing pipe can meet the use requirements of the current and future markets for the geothermal well casing pipe.

Description

Casing for geothermal well and manufacturing method thereof

Technical Field

The invention belongs to the technical field of low alloy steel manufacturing, and relates to a casing for a geothermal well and a manufacturing method thereof.

Background

Geothermal resources are renewable, novel, environment-friendly and clean energy and have great application potential. With the technical progress, a brand new energy utilization form can be created by developing and applying geothermal resources, so that the energy consumption structure can be optimized, the resources are saved, the environment is improved, and the pollution and haze treatment effects are very obvious. In recent years, with the increasing attention on energy and environment, the development and utilization of geothermal resources become a key measure for realizing the combination of fossil energy and new energy from the perspective of low-carbon economy. The working conditions of the geothermal well are complex, the geothermal well bears the combined action of temperature and a large amount of corrosive media and the like, and the tubular product for the geothermal well is very easy to generate failure modes such as leakage, corrosion, deformation, fracture and the like after being in the high-temperature and corrosive media for a long time, so that the later maintenance, modification and well repair expenses are increased, the economic cost and the service life of the development of the geothermal well are influenced, even environmental pollution is caused, and the vigorous development and effective utilization of geothermal resources are limited. These factors determine that the performance of the casing for exploiting geothermal resources plays an important role, and a high-temperature-resistant and corrosion-resistant casing suitable for exploiting geothermal energy needs to be developed so as to achieve the purposes of safe exploitation, yield increase and efficiency increase.

The depth of the geothermal well is generally 1000-4000 meters, the temperature is generally divided into high temperature, medium temperature and low temperature, and when the temperature is higher than 150 ℃, the geothermal well belongs to high-temperature geothermal in the form of steam; the temperature is between 90 ℃ and 150 ℃, exists in the form of a mixture of water and steam and the like, and belongs to medium-temperature geothermal energy; the temperature is higher than 25 ℃ and lower than 90 ℃, and the heat-preserving material exists in the forms of warm water, warm hot water, hot water and the like, and belongs to low-temperature geothermal energy. The higher the geothermal well temperature, the stronger the corrosive effect on the metal. In the aspect of pipe design, the pipe for geothermal resources at the present stage adopts a traditional strength design method, namely a stress design method, and is based on the theory of elastic mechanics to ensure that the pipe cannot yield. The stress design method mainly considers the strength index of the pipe, can meet the requirements of drilling and completion engineering, considers the action of thermal stress, and can meet the condition that the pipe cannot yield under the high-temperature condition. In fact, the existence of the casing loss forms such as deformation, necking, shearing, fracture and the like of the tube for geothermal resources fully indicates that the tube is actually subjected to plastic deformation in the service process, and different plastic deformations cause permanent deformation and even fracture failure of the tube. Therefore, the pipe designed according to the stress lacks large deformation resistance required by operation, and the permanent deformation capacity of the pipe under the complex working condition of the geothermal well is not considered in the pipe selected by the existing geothermal well.

The corrosion of the tube for the geothermal well is mainly corrosion of geothermal fluid and soil, and mainly electrochemical corrosion. Generally, geothermal water has high mineralization degree and more ion types, and mainly comprises chloride ions, dissolved oxygen, sulfate ions, hydrogen sulfide, carbon dioxide and the like, wherein the corrosivity of the chloride ions is the strongest, and the chloride ions are important factors for causing uniform corrosion, hole corrosion and crevice corrosion of carbon steel, stainless steel and other alloys. In addition, the relative motion between the corrosive fluid and the surface of the well tubular metal causes accelerated wear corrosion of the metal, which is also known as "shock corrosion", erosive corrosion or abrasion corrosion, which increases in speed especially when the sand content is high during pumping. In the service process of the underground pipe column, the pipe column is simultaneously subjected to combined action of composite loads, including pulling up, compression, internal pressure, external pressure, torsion, welding residual stress and the like, and the combined action of the forces and a specific corrosion medium generates stress corrosion, so that the metal is cracked. Therefore, the requirement of designing and manufacturing a special sleeve for the corrosion working condition of the geothermal well is required, and the aims of low-cost safe development and long-term effective utilization of geothermal resources are met.

The common corrosion prevention mode at present adopts internal corrosion prevention, non-metal pipes, corrosion allowance increasing of the pipes, corrosion-resistant alloy materials and the like. The carbon steel material can be protected for protecting an inner anti-corrosion coating, a plating layer and a lining, such as nickel-phosphorus plating, SK-54 anti-corrosion, nitriding treatment, titanium nano coating, a stainless steel lining and the like, but the problems of poor bonding force of the coating, large-area falling and the like in the use process cannot be effectively reduced because the yield stress of the carbon steel and the anti-corrosion coating (plating layer and lining) is different, the requirements on the internal surface smoothness of a pipe body are higher mostly, the operation process is complex, the manufacturing cost is high, the plating layer is uneven, and the problems of poor bonding force of the coating, large-area falling and the like exist. The corrosion-resistant coating has strong corrosion resistance for nonmetal pipes such as PVC-U plastic pipes, glass steel pipes and the like, can effectively avoid the problems of corrosion and scaling, but has the technical problems of no high temperature resistance, low strength, bearing, heat resistance, aging, joint treatment and the like, and prevents the large-scale use of the coating in geothermal wells. The design of increasing the corrosion allowance of the pipe, namely increasing the thickness of the pipe wall, needs to monitor the corrosion rate of the material according to the expected service life of the pipe and the medium, and determines the corrosion allowance. The design needs to analyze the pipe performance influence factors and correctly evaluate the size of the corrosion allowance, can not solve the problem of local corrosion, and can further increase the economic cost of geothermal resource development.

In view of the above, there is a need to develop a new geothermal well casing that can resist high temperature and corrosion.

Disclosure of Invention

The invention aims to overcome the defects that the common tube corrosion prevention mode for geothermal wells is high in cost and cannot resist high temperature and corrosion in the prior art, and provides a sleeve for geothermal wells and a manufacturing method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

the chemical composition of the casing for the geothermal well comprises, by mass, 0.18-0.30% of C, 0.20-0.35% of Si, 1.25-1.45% of Mn, 0.85-1.55% of Cr, 0.10-0.5% of Mo, 0.15-0.30% of Ni, 0.01-0.1% of V, 0.01-0.05% of Ti, 0.02-0.5% of Nb, 0.015-0.040% of W, 0.10-0.30% of Cu, 0.015-0.035% of Al, and 0.001-0.002% of B, and also comprises P and S, wherein the maximum content of P is 0.010%, the maximum content of S is 0.005%, and the balance is Fe and inevitable impurities.

Preferably, the yield strength of the geothermal well casing is greater than 552MPa and the tensile strength is greater than 655 MPa.

Preferably, the geothermal well casing has a V-notch, and the charpy impact work of the V-notch is greater than 30J.

Preferably, the average corrosion rate of the geothermal well casing is less than 0.2 mm/a.

A preparation method of a sleeve for a geothermal well comprises the processes of converter smelting, continuous casting, heating, tension reducing and straightening of a pipe blank in sequence.

Preferably, the converter smelting and continuous casting process further comprises the process of inspecting the components, the macrostructure and the surface quality of the tube blank, and the next operation is carried out when the alloy components, the inclusion content, the size and the surface quality meet the standard requirements.

Preferably, the heating process comprises ring furnace heating, piercing, tube rolling and reheating.

Preferably, the heating temperature of the annular furnace is 1200-1300 ℃; the temperature of the reheating process is 930-980 ℃.

Preferably, the tapping temperature is at least 880 ℃ during the tension reducing process; the tube blank is further subjected to air cooling after the tube blank is subjected to tension reducing.

Preferably, the temperature of straightening is at least 320 ℃.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a sleeve for a geothermal well, which ensures the strength, improves the high temperature and corrosion resistance of a pipe by controlling the content of C, and controls the content of P, S, because the lower the content of P, S, the better the corrosion resistance, and the adjustment of the content of Cr, Ni, Mo, Si and Cu elements is beneficial to improving the pitting corrosion, thereby improving the pitting corrosion resistance of the sleeve material. The bonding force among atoms is improved through solid solution strengthening of Cr, Mo, W and Nb elements, the activation energy is increased, a stable second phase is formed, the thermal stability of the material is improved, and meanwhile, the pipe has certain corrosion resistance; si, Al and other elements can form a compact oxide structure, so that the oxidation resistance and the corrosion resistance of the material are improved, and the grain size of the material is controlled. The performance indexes of the casing for the geothermal well are as follows: the yield strength is more than 552MPa, the tensile strength is more than 655MPa, and the Charpy impact energy of the V-shaped notch sample is more than 30J; the average corrosion rate is less than 0.2 mm/a. Therefore, the geothermal well casing pipe can meet the use requirements of the current and future markets for the geothermal well casing pipe.

The invention also discloses a manufacturing method of the sleeve for the geothermal well, and the manufacturing process comprises the steps of converter smelting, continuous casting, heating, tension reducing and straightening in sequence; moderate alloy cost, no need of special heat treatment process, reduced processing energy consumption, shortened production and delivery cycle, and better market competitiveness of the product.

Furthermore, the tube blank smelted and continuously cast by the converter needs to be checked for components, macrostructures and surface quality, and whether the alloy components, the inclusion content and the size meet the standard requirements or not is determined, so that the quality of the tube is ensured. The macrostructure should not have macroscopic residual shrinkage cavity, peeling, layering, air bubbles, sand holes, white spots, cracks and non-metallic inclusions, and the surface quality of the tube blank does not allow the defects of scabbing, cracks, hairline, groove, folding, dents, ears, air holes, pockmarks, sand holes and the like.

Furthermore, the temperature is strictly controlled in the heating process of the annular furnace, and the defects of overheating, overburning, decarburization and the like are not allowed to be generated; reheating, performing tension reducing, determining the outer diameter of the pipe according to design requirements, and controlling the precision within the range of standard requirements; the tapping temperature is controlled to be more than or equal to 880 ℃, then air cooling is carried out, the required ferrite and pearlite structures can be obtained, the straightening temperature is at least 320 ℃, and therefore the stability of hot rolling performance can be guaranteed, and the deformation resistance of the prepared casing for the geothermal well can be further guaranteed.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is to be understood that the terms in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below:

a tubular product for a geothermal well comprises the following chemical components in percentage by weight:

c: 0.18-0.30%; si: 0.20-0.35%; mn: 1.25-1.45%; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; cr: 0.85-1.55%; mo: 0.10 to 0.5 percent; ni: 0.15-0.30%; v: 0.01 to 0.1 percent; ti: 0.01 to 0.05 percent; nb: 0.02-0.5%; 0.015 to 0.040 percent of W; cu: 0.10-0.30%; al: 0.015-0.035%, 0.001-0.002% of B, and the balance of Fe and inevitable impurities.

A manufacturing method of a sleeve for a geothermal well comprises the following manufacturing processes of converter smelting, continuous casting, heating in a circular furnace, perforating, pipe rolling, reheating, tension reducing and straightening in sequence; wherein, the tube blank smelted and continuously cast by the converter is subjected to component, macrostructure and surface quality inspection; heating the mixture in an annular furnace to 1200-1300 ℃; and then heating to 930-980 ℃, reducing the diameter by tension, controlling the tapping temperature to be more than or equal to 880 ℃, and then cooling by air to ensure the hot rolling performance to be stable, wherein the inlet temperature of the steel entering a straightening machine is more than or equal to 320 ℃.

The chemical compositions of the pipes prepared in the examples are shown in Table 1, and the technological processes are converter smelting, continuous casting, heating in a circular furnace, perforation, pipe rolling, reheating, tension reducing and straightening.

TABLE 1 chemical composition of pipes prepared in examples (mass fraction,%)

Note: the balance of Fe and inevitable trace impurities.

The results of the main mechanical properties of the pipes prepared in the above examples 1-3 are shown in Table 2.

TABLE 2 Main mechanical properties of the pipes prepared in examples 1-3

As can be seen from Table 2, the mechanical properties of the pipe are superior to those of the pipe for geothermal well exploitation at the present stage (yield strength range 379-552MPa, tensile strength 517MPa), and the toughness meets the requirements of the pipe for geothermal well exploitation on performance.

The corrosion performance results for the pipes prepared in the above examples are shown in table 3.

TABLE 3 Corrosion resistance of the pipes prepared in examples 1-3

The corrosion rates of Q345R in geothermal water at 30 ℃, 60 ℃ and 90 ℃ are 0.86mm/a, 3.02mm/a and 8.96mm/a, as known from the literature [1 ]. The document [2] shows that the corrosion resistance evaluation of 8J 55 casing pipes in Luo river water of Changqing oil fields shows that the average corrosion rate is 0.025-0.12 mm/a, and the maximum corrosion rate is about 2.4 mm/a. Document [3] indicates the tendency of the corrosion rates of the two materials K55 and J55 to change at different NaCl concentrations and temperatures. As can be seen from Table 3, the corrosion rate of the casing for geothermal well manufactured by the invention is 0.15mm/a on average, and the corrosion resistance of the casing is better than that of the casing for geothermal well manufactured by the prior art.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Reference to the literature

[1] Liu Zheng Tong, Yang Xiao Yu, Zhao Jie, anyi, Q345R Steel corrodes and scales in simulated geothermal water environment [ J ]. the proceedings of Beijing institute of petrochemical industry, 2015,23(3):30-34.

[2] The corrosion resistance of 8 kinds of J55 sleeves in Changqing oilfield Luohui water was evaluated [ J ] corrosion and protection, 1999,20(6): 259-.

[3] The corrosion characteristics of the Dingyichuan thermal production well string under the environments of chloride ions and acid gases are researched [ M ]2020:31.

Claims

1. The sleeve for the geothermal well is characterized by comprising, by mass, 0.18-0.30% of C, 0.20-0.35% of Si, 1.25-1.45% of Mn, 0.85-1.55% of Cr, 0.10-0.5% of Mo, 0.15-0.30% of Ni, 0.01-0.1% of V, 0.01-0.05% of Ti, 0.02-0.5% of Nb, 0.015-0.040% of W, 0.10-0.30% of Cu, 0.015-0.035% of Al, and 0.001-0.002% of B, and further comprising P and S, wherein the maximum content of P is 0.010%, the maximum content of S is 0.005%, and the balance is Fe and inevitable impurities.

2. The geothermal well casing according to claim 1, wherein the geothermal well casing has a yield strength of greater than 552MPa and a tensile strength of greater than 655 MPa.

3. The geothermal well casing according to claim 1, wherein the geothermal well casing has a V-notch, and the charpy work of the V-notch is greater than 30J.

4. The geothermal well casing according to claim 1, wherein the average corrosion rate of the geothermal well casing is less than 0.2 mm/a.

5. A preparation method of a sleeve for a geothermal well is characterized by comprising the steps of converter smelting, continuous casting, heating, tension reducing and straightening of a pipe blank in sequence.

6. The preparation method according to claim 5, characterized in that the converter smelting and continuous casting process further comprises the process of inspecting the components, macrostructure and surface quality of the tube blank, and the next operation is carried out when the alloy components, the inclusion content, the size and the surface quality meet the standard requirements.

7. The method of claim 5, wherein the heating process comprises ring furnace heating, piercing, tube rolling, and reheating.

8. The preparation method according to claim 7, wherein the temperature of the annular furnace is 1200-1300 ℃; the temperature of the reheating process is 930-980 ℃.

9. The method of claim 5, wherein the tapping temperature during the stretch reducing process is at least 880 ℃; the tube blank is further subjected to air cooling after the tube blank is subjected to tension reducing.

10. A method as claimed in claim 5, characterized in that the temperature for straightening is at least 320 ℃.