RU2667919C1 - Method of threaded connections sealing increase of circular and pump-compressor (lift) columns - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: method of increasing the tightness of threaded joints of casing and tubing (lift) columns refers to the petrochemical industry and can be used to provide reliable and long-lasting sealing of joints, when assembling threaded joints, including in the conservation of threaded joints, drilling, tubing and casing pipes, including various options for "metal-to-metal" sealing, when operating pipes in oil, gas, gas condensate fields, water injection wells.EFFECT: ensuring the stability of the operational properties of the GHS, such as reducing the moment of screwing, the absence of plastic deformation of the threaded joint, including in the "metal-metal" sealing zone, reliable sealing due to the selection of the size of the fillers, depending on the roughness of the surface of the threaded joint elements, which makes it possible to adjust the composition of the lubricant by selecting the fractional composition of the solid elements in the lubricant, depending on the quality of the thread, calculated by the formula: particle size, mcm ≤ 2Ra, where Ra is the smallest roughness value of the two contacting surfaces, which results in blocking the leakage of oil or gas.1 cl, 3 tbl

Description

A method of increasing the tightness of threaded joints of casing and tubing (elevator) columns relates to the petrochemical industry and can be used to ensure reliable and long-term sealing of joints when assembling threaded joints, including the preservation of threaded joints, drilling, tubing and casing pipes, including those with various metal-metal sealing options, when operating pipes in oil, gas, gas condensate fields, and water injection wells.

The average duration of exploitation of gas fields is 25-30 years. However, there are gas fields with special operating conditions, the planned life of which is defined in 80-90 years (Astrakhan gas condensate field).

The duration of the exploitation of oil fields has not been officially announced, and the service life of 50-100 years is not a record for them.

When drilling wells, the trunk crosses various formations, including gas, with drinking water used by the population. The need to exclude cross-flow from one formation to another, and gas to surface during the entire life of the wells is the most important task facing the oil industry and its production.

Accelerated development of the Romashkinskoye field in the war and post-war years, insufficient attention to ensuring environmental safety during the assembly and casing stringing led to the fact that a number of territories in Tataria and Bashkiria were declared zones of environmental disasters.

A large “contribution” to the formation of cross-flows is made by the leakage of threaded joints, which has been increasing in recent decades due to the widespread introduction of directional, gentle and horizontal drilling. An important role in the mentioned process is played by threaded sealing lubricants used in the assembly of threaded joints in the field and in the production of pipes. Currently, a number of pipe rolling plants use imported lubricants for compounds of some designs.

Threaded sealing greases are recommended for lubricating and sealing all threaded oil assortment pipes.

In accordance with the above, the main tasks of threaded sealing lubricants include:

- ensuring the necessary, long-term tightness of threaded joints of various designs (fill in all the structural clearances), especially when operating threaded oil assortment pipes;

- the exception of scoring on the surfaces of the threaded and sealing parts of the connection when screwing and unscrewing;

- ensuring the assembly of the connection not only with a regulated moment, but also the fulfillment of the assembly criteria: a make-up diagram that matches the reference assembly schedule, the relative position of the connection elements and others;

- prevention of plastic deformation of thread elements;

- uniform lubrication of the entire surface, preventing the formation of "dry" friction zones, "bridges" of cold welding;

- preventing obstruction of contacting surfaces, including thrust surfaces, of all metal-metal sealing elements (cone-cone, cone-sphere and the like);

- reduction of wear of all elements of the threaded connection (weight loss, resizing, changing the tightness) of the parts after repeated screwing-unscrewing, especially for the operation of tubing in underground and overhaul wells.

During the construction, operation and repair of wells, various types of oil-cut tubing are used.

At least 5 casing strings and one tubing string are present in the well design.

Each type of pipe has its own design of threaded joints, its own operating conditions, which determines certain operational requirements for threaded sealing lubricants:

- for threaded joints of casing pipes: long tightness of the joint, commensurate with the life of the field, low coefficient of friction;

- for tool joints of drill pipes: short-term (within drilling) tightness, increased coefficient of friction, high anti-wear and extreme pressure properties;

- for threaded connections of tubing: ensuring tightness during technological operations and / or for the life of downhole equipment (1-5 years); anti-wear properties - ensuring the maximum possible, but not less than 10-20 cycles of screwing-unscrewing without damage and a significant change in the geometry and tightness of the thread.

To ensure the tightness of the threaded joints of the casing and tubing (elevator) columns, lubricating and sealing means (hereinafter referred to as GHS) are used, which are referred to as operational lubricants and are intended for the assembly of tool joints of drill pipes, threaded joints of the tubing and casing, including including with various metal-metal sealing options when operating pipes in oil, gas, gas condensate fields, and water injection wells, providing anti-wear properties TWA and long sealing compounds. GHS can be used to preserve threaded connections.

It is known from the prior art that the performance properties of a lubricant for threaded joints of oil grade pipes must meet the ISO 13678 (API 5A3) standard “Oil and gas industry - evaluation and testing of threaded lubricants for joints of casing, tubing, pipe for pipelines and drill elements columns ".

Standards ISO 13678, API 5A3 and developed on their basis GOST R ISO 13678 give the following lubricant composition.

The standard grease is designed for standard “triangular” or “smooth” threads according to (API 5B), while being positioned as universal, i.e. suitable for any type of threaded connection, any pipe operated in any conditions. When choosing the sieve composition of metal fillers, the developers focused on the technological level of production and the manufacturing accuracy available at that time (tolerances). The larger the tolerances, the greater the gaps to be sealed. This explains the requirement (recommendations) for the presence in the lubricant of metal particles of lead filler in size from 299 microns to 150 microns in an amount of up to 1%, and up to 25% of particles larger than 75 microns.

The ISO 13678, API 5A3 standards and GOST R ISO 13678 developed on their basis establish requirements for the physicochemical properties of threaded greases and for ensuring the tightness of threaded joints.

To operational properties:

- do not form scoring on the surfaces of the threaded and sealing parts of the connection when screwing and unscrewing;

- to ensure the assembly of the connection not only with a regulated moment, but also to ensure the fulfillment of the assembly criteria: a make-up diagram that matches the reference assembly schedule, the relative position of the connection elements, etc .;

- not cause plastic deformation of thread elements;

- uniformly lubricate all surfaces, prevent the formation of "dry" friction zones, "bridges" of cold welding;

- do not impede the closure of contacting surfaces, including thrust surfaces, of all metal-metal sealing elements (cone-cone, cone-sphere, etc.);

- reduce the wear of all elements of the threaded connection (weight loss, resizing, changing the tightness) of the parts after repeated screwing-unscrewing, especially for the operation of tubing in underground and overhaul wells.

In the early 80s, modern CNC machines were widely introduced for threading in pipe joints of oil assortment. As a result, manufacturers were able to ensure the production of threads with tighter tolerances. In particular, due to this, it became possible to supply threads of all profiles with small gaps and high performance. Since the advent of API 5B joints, the leakage resistance of the joints has been associated with the particle size of the thread lubricants and the clearance in the thread. The recommended sieve composition of metal fillers has not been revised and remains unchanged since the 70s (reference to API 5B). The sizes of metal particles recommended there (150 microns and more), ensuring the tightness of the threaded joints of the thread, became "too" large at the current level of thread cutting.

Tubing connection: Nominal clearance in the thread of the tubing according to GOST 53366-2009 z = 0.076 mm (76 μm). The side faces are in contact with each other, there is no gap.

OTTM connection according to GOST 632-80 table 16: taking into account the maximum tolerance, the gap is 2.48-2.29 = 0.22 mm, taking into account the tolerance on the tool, the remaining faces are in contact with the counterpart of the thread.

Connection “Butress” according to GOST R 51906-2002: taking into account the maximum tolerance, the gap in the thread. 2.65-2.41 = 0.24 mm on the sides, the remaining faces are in contact with the counterpart of the thread.

Connections with a metal-to-metal seal in the threaded part have a gap in the power part of 0.15-0.24. There is no clearance in the sealing part.

In the modern edition of the API standard RP 5A3 and documents harmonized with it, the main task of lubrication also remains to ensure the tightness of the threaded connection. The appendices to the standard do not have a test method for anti-wear properties and evaluation criteria.

Conventional “standard” and “modified” thread greases made using the recommended fillers ISO 13678 (API RP 5A3) may not provide the above properties and are unsuitable for assembling joints with the metal-metal seal assembly, since in lubricating compositions with such fillers there are large metal particles that are comparable or significantly exceed the size of the gap in the threaded connection.

This is manifested by the instability of the make-up parameters, that is, when making with the same moment, the final position of the coupling is different. This is due to the presence of large particles in the lubricant, with an uneven distribution in the lubricant volume. Lubricants of a standard composition are characterized by an unstable coefficient of friction, a high moment of screwing and unscrewing of a threaded joint, a lack of guaranteed and prolonged sealing of the joint, uneven distribution over the thread, additional stresses, and no dependence of the sieve composition and shape of the filler particles.

Also known as "Lubricant for sealing threaded connections" according to the patent of the Russian Federation No. 2032712, IPC С10М 169/04, publ. 04/10/1995, containing, by weight. %: calcium grease 7-15; graphite 30-40; water 0.5-8; mineral oil - the rest, the use of which does not provide a long-term operational guarantee of the tightness of the assembled joint.

To ensure the tightness of threaded joints, grease-based thread-sealing greases with fillers in the form of powders (graphite, vermiculite, zinc, lead, aluminum, copper and others) are widely used.

From copyright certificate No. 1413123, publ. 07/30/1988, IPC С10М 169/04, it is known to use aluminum powder in a lubricant as a metal filler, in which, in order to increase its anti-seize antifriction properties, it is introduced into the composition, wt. %: aluminum powder 4-10; graphite powder 4-10 and liquid glass the rest.

In this technical solution there is no connection between the size and amount of powder in the lubricant with the roughness of the sealing (contacting) surfaces; assembly of the joint can be carried out only 16-24 hours after applying grease to the threaded surface, which is completely unacceptable for the manufacturer or for work on the drilling rig. The reference to 100% tightness in the manufacturer's conditions, where the pressure is maintained with the liquid for 10 seconds, does not mean the tightness of the connection, but the strength of the pipe body.

Closest to the claimed technical essence and achieved by using the technical result is a lubricant for sealing threaded joints "RUS-Premium" TU 0254-008-54044229-2005 according to the patent of the Russian Federation No. 2355740, IPC С10М 169/04, publ. 05/20/2009, which has in its composition, wt. %: oil IGP-18 24-30; LKS-M 8-19; copper 8-10; GLS graphite - the rest.

In the listed lubricants there is no connection between the surface roughness of the elements of the threaded connection and the size of the metal fillers in the lubricant, which also applies to the above-mentioned known lubricant for sealing threaded joints "Rus-Premium", manufactured according to the technical specifications TU 0254-008-540044229- 2005 in accordance with the patent for invention RU 2355740, IPC С10М 169/04, publ. 05/20/2009, adopted as a prototype of the inventive lubricating-sealing composition.

Since metal fillers of known compositions have a hardness close enough to the hardness of the steel of which the pipe is made, the abrasive effect of, for example, copper and zinc, on the elements of the threaded connection, sealing and threaded surfaces. This is manifested with the formation of micro-seizes, which, in turn, significantly reduces the sealing properties of the compound, especially in gas wells. Under the influence of a hydrocarbon medium, chemical reagents, and others, the fat base of the composition gradually dissolves (squeezed) out of threaded joints over time, which leads to a loss of tightness of the joint and, as a result, to the need for costly well repair.

One of the main functions of metal powders is to prevent seizing during screwing-unscrewing threaded joints of casing and tubing.

When choosing a filler, the applicant was guided by the parameters of metal fillers recommended by ISO 13678.

Physical properties:

Copper - density 8.92 g / cm ³ , soft, malleable metal: Brinell hardness: electrolytic copper 28-30 kgf / mm ² , deformed copper 53 kgf / mm ² ; due to hardening, the tensile strength of copper increases to 80 kgf / mm ² .

Zinc is a metal of medium hardness. It is fragile when cold. The density of solid zinc is 7.133 g / cm ³ (20 ° C), Brinell hardness is 8-10 kgf / cm ² . At room temperature, zinc is brittle, at 100-150 ° C it becomes ductile and rolled into thin sheets and wire, at 200-250 ° C it becomes very brittle, m. crushed into powder.

Lead is one of the low-melting metals, heavy non-ferrous metal: density, g / cm ³ : 11.3415 (20 ° С). Lead is soft, plastic, Brinell hardness of 4-4.2 kgf / mm ² .

The objective of the proposed technical solution is to ensure the stability of the operational properties (reliability and durability) of the lubricant seal for sealing the threaded joints of casing and tubing (elevator) columns, including those with various metal-metal sealing options, when operating pipes in oil and gas gas condensate fields, water injection wells.

The problem is solved by a method of increasing the tightness of threaded joints of casing and tubing (elevator) columns by selecting metal fillers of a lubricant-sealing agent, while the fractional composition of the fillers is determined by the properties of the threaded surface and calculated by the formula: filler particle size, μm ≤ 2Ra, where: Ra is the smallest roughness value of one of the two contacting surfaces.

Such a choice of the fractional composition of the fillers, when the minimum size of the filler fraction (diameter or thickness) is equal to or less than twice the smallest roughness value of one of the two contacting surfaces, allows to “smooth” the thread roughness to the maximum.

The method is as follows.

The performance properties of threaded greases can be adjusted by fractional and percent solids.

It is impossible to create a lubricant that provides 100% coincidence of the total free volume of the assembled threaded joint and the volume of solid elements, even if the mating parts are made on one machine and one tool.

The most realistic is the selection of a solid filler, depending on the surface roughness of the various elements of the threaded connection: the threaded part and the sealing part.

Selection of a metal filler (copper, zinc, lead, tin, bronze, aluminum, including their mixtures, salts and / or alloys of the above metals) by shape, sieve composition, volume and quantity, regardless of the type of dispersion medium and thickener, and the presence of other non-metallic fillers (graphite, polymer fillers, vermiculite, talc, microcalcite, chalk and other mineral fillers having a Moss hardness of 4 or less) are produced depending on the roughness of the contacting threaded and / or sealing surfaces. This ensures that the assembly criteria of the threaded connection are met and, accordingly, provides the calculated functioning of the threaded connection.

Let us analyze the example of threaded joints of casing pipes: “OTTG” and VMZ-1.

Where:

V _"OTTG" - the volume of the sealing part of the threaded connection "OTTG";

Ra is the smallest roughness value of one of two contacting surfaces;

2Ra _“OTTG” = 0.005 mm - twice the lowest value of the roughness of two contacting surfaces;

V _VMZ-1 - the volume of the sealing part of the threaded connection VMZ-1;

2Ra _VMZ-1 = 0.0032 mm - twice the lowest value of the roughness of two contacting surfaces;

Thus, the "free" volume to be sealed for the same structural thread element on the same area depends on the value of Ra, in our example it has a difference of 1.5625 times.

Any threaded connection, depending on the functional purpose, can be conditionally divided into “elements” or “parts”.

The threaded metal-metal connection is structurally divided into power and sealing "parts", the roughness values of which vary significantly. The threaded grease must have anti-seize properties for the power and sealing parts with a metal-to-metal seal. Damage to the metal-metal seal assembly will result in a leak in the threaded joint.

To fulfill these conditions, it is necessary that the solids content be in the range of not more than 85% of the volume of structural gaps, and the particle size in microns ≤ 2Ra, where Ra is the roughness size of the “element / particles” with the smallest roughness value of the two contacting surfaces.

A thread grease with the same content of metal fillers, but differing in size, will have anti-seize properties for a threaded joint with a roughness Ra _OTTG , but for a threaded joint with a roughness Ra _VMZ-1 will be unsuitable.

Let us consider the operation of a lubricating-sealing agent using the example of assembly of casing pipes with these threaded joints VMZ-1 and OTTG.

In OTTG compounds, the roughness of the contacting sealing surface is Ra = 2.5 μm (GOST 632), and the roughness of the sealing surface of VMZ-1 is _Ra = 1.6 μm (KD OJSC Vyksa Metallurgical Plant).

At the beginning of screwing the VMZ-1 threaded connection, the gap between the contact sealing surfaces with an interference fit of 5 mm and a given contact width of 9 mm (specified by the design documentation) will be 0.4 mm. With further make-up (advance along the axis by 4 mm), the initial contact of the sealing surfaces occurs, and the gap between the protrusions of the roughness will be 0 mm. The "extra" plastic base is "squeezed out" of the gap until the surfaces completely close. The distribution of filler particles with sizes ≥ 2Ra over the surface is possible until the moment when the gap size is commensurate with the size of the filler. Further, under the influence of torque, the "captured" filler particles must undergo plastic deformation. For this, it is necessary to apply an additional moment, which leads to plastic deformation of the threaded part and the "under-rotation" of the threaded connection.

For threaded connections with a metal-metal seal, this will lead to size disruption, the absence of a design contact pressure on the sealing surfaces, and the absence of a metal-metal contact. Threaded connection will not provide tightness. When unscrewing, the geometric dimensions of the thread elements will be violated due to hardening and plastic deformation during make-up, which makes repeated make-up and operation impossible.

The distribution of filler particles with sizes ≥ 2Ra over the surface is possible up to the moment when the gap size is commensurate with the size of the filler and in this case, the distribution will occur until the gap is 2Ra. Further, under the influence of torque, the “captured” filler particles are distributed over the surface, smoothing and smoothing the roughness. In this case, there is no plastic deformation, but an increase in the contact area of the surfaces and the formation of a compensation or corrective or insulating-sealing layer.

The metal filler does not have an abrasive effect, hardening does not occur, and there is no plastic deformation. When unscrewing, the geometric dimensions of the thread elements are not violated due to plastic deformation during make-up, which makes it possible to re-make and operate pipes with a metal-metal seal. Fillers of the lubricating-sealing agent “clogging” the said volume (formed by roughness) increase the tightness of the joint.

Threaded joints with a surface roughness of Ra 2.5 μm (OTTG connection) have a gap volume at the initial contact of irregularities almost one and a half times greater than with Ra 1.6 μm, a Premium connection (2.5 / 1.6 = 1.5625).

The sealing ability of the compound is proportionally reduced. Accordingly, the maximum size of solid fillers in contact to ensure guaranteed tightness should be increased.

Thus, the particle size of the GHS metal filler used in the assembly of sealing surfaces with Ra 2.5 μm should be larger than 1.5625 larger than when used on surfaces with Ra 1.6 μm, which is achieved by selection of the composition, but not exceed size ≤ 2Ra.

The technical effect of the proposed technical solution is to ensure the stability of the GHS operational properties, such as reducing the make-up torque, the absence of plastic deformation of the threaded joint, including in the metal-metal sealing zone, reliable sealing, by selecting the size of the fillers depending on the surface roughness of the elements threaded connection, which provides the possibility of adjusting the composition of the lubricant by selecting the fractional composition of solid elements in the lubricant, depending on the quality of the thread, and calculated by the formula: particle size, μm ≤ 2Ra, where: Ra is the smallest roughness value of two contacting surfaces, which leads to blocking the leakage of oil or gas.

Literature

1. Gudima N.V., Shane Y.P. A quick reference to the metallurgy of non-ferrous metals. M., 1975.

2. 3aitsev V.Ya., Margulis E.V. Metallurgy of lead and zinc M., 1985.

3. Kozin L.F., Morachevsky A.G. Physical chemistry and metallurgy of high-purity lead. M., 1991.

4. Smirnov M.P. Lead refining and processing of intermediate products M., 1977; Rabinovich V.A., Khavin Z.Ya. Brief chemical reference. L., 1977.

5. “Friction, Wear, and Lubrication,” Handbook, Volume 1, Moscow, “Mechanical Engineering,” 1978, edited by I.V. Kragelsky and V.V. Alice.

Claims (1)

A method of increasing the tightness of threaded joints of casing and tubing (elevator) columns by selecting metal fillers of a lubricating-sealing agent, characterized in that the fractional composition of the fillers is determined by the properties of the threaded surface and calculated by the formula: filler particle size, μm ≤ 2Ra, where Ra - smallest roughness value of two contacting surfaces.