RU2607935C2 - Self-packing package for asymmetric chevron collars - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: invention relates to self-compacting package of asymmetric chevron seals, which serves for installation in wellhead sealing gaskets of moving polished rod. Package consists of at least two asymmetric collars installed in case of wellhead gland, support and pressure sleeve with self-sealing gate effect with minimum friction force in area of contact sealing edges asymmetric cups with surface of the polished rod, and is able to seal moving polished rod without axial compression package seals, with multiple increase of service life of seals without replacement, increasing service life of polished rod, reduction of power consumption for pumping drive.

EFFECT: prevention of oil spills, environmental pollution and prevention of frequent stops process of oil production with mechanised method with application of sucker rod pumps.

1 cl, 2 dwg

Description

The invention "Self-sealing package of asymmetric chevron cuffs" relates to a sealing technique and can be used to seal long (over 2000 mm) polished rods moving with high axial speed (from 0.3 to 3 m / s), in particular for installation in wellhead oil seals with oil using sucker rod pumps (SHG).

One of the main reasons for stopping the continuous process of oil production using sucker rod pumps is the premature failure of replaceable seals due to increased friction in the contact zone of the seals with the surface of the polished rod and loss of tightness of the wellhead seal, which leads to oil spills at the wellhead and contamination the environment. The increased friction force occurs due to the uncontrolled compression force of the seal pack in the axial direction, as a result, the work of the friction force is converted to heat, the temperature in the contact zone of the sealing lips of the cuffs with the stem surface rises, which leads to overheating of the seals and premature failure, especially in the period of "dry friction" in the absence of fluid in the wellhead seal.

Known rubber-fabric chevron multi-row seal used for installation in wellhead glands, consisting of chevron cuffs, support and pressure rings according to GOST 22704-77, selected as a prototype.

The disadvantage of this device is the inability to ensure tightness in the contact area of the sealing lips of the cuffs with the surface of the polished rod without axial compression, therefore, multi-row seals according to GOST 22704-77 effectively seal the polished rod only with axial compression of the seals with a large uncontrolled force F (Figure 1), contributing to an increase in the friction force in the stuffing box assembly, premature failure of seals, premature wear of the surface of an expensive polished rod, increased power consumption during the operation of the rocking machine. The pressure nut of the wellhead stuffing box (see Bukhalenko EI, Abdullaev Yu.G. “Installation, maintenance, repair of oilfield equipment.” M .: “Nedra”, 1985, p. 42-45) oil production operators delay using a screwdriver with a torque M = 20 ÷ 30 kg⋅m, in this case, the force F = M / t €, where € is the angle of the thread turns, for the M76x3 thread used in wellhead seals in the pressure nut, the angle of the coil turns is 2 ° 15 '', t € = 0,03947, force F = 30 / 0,03947 = 760 kg, chevron cuffs are crushed with such force, pressing against the surface of the stem, and create a high friction force. The cuff design drawbacks include the symmetry of the inner and outer cuff shoulders in the cross-section of Figure 1, since axial compression of a pack of chevron cuffs according to GOST 22704-77 results in the closure of the surfaces of the inner and outer shoulders of adjacent cuffs, which limits further compression of the inner shoulders of the cuffs to the rod, that is, the preload is one-time.

The invention is aimed at ensuring tightness in the contact area of the sealing edges of the chevron cuffs with the surface of the polished rod in combination with the minimum friction force due to the self-sealing effect of asymmetric chevron cuffs interacting with each other.

The technical result is achieved by the fact that the lower and upper cuffs in contact have different angles of inclination of the surfaces, which act on each other in the axial direction and the cuff shoulders (internal and external) are asymmetric.

The invention is illustrated by drawings.

Figure 1 - cross section of a multi-row chevron seal according to GOST 22704-77.

Figure 2 is a cross section of a self-sealing package of asymmetric chevron cuffs.

A self-sealing package of asymmetric chevron cuffs is fitted with an interference fit into the housing (item 1) of Figure 2, is supported by a support sleeve (item 3) and consists of at least two cuffs (Figure 2 shows a package of three cuffs), on top of the package there is a push sleeve (item 4). The maximum number of cuffs is not limited, but eight cuffs are enough for the working chamber of the wellhead stuffing box, this conclusion was obtained experimentally as a result of pilot industrial tests in oil wells equipped with sucker rod pumps at the enterprises: OAO Lukoil, OAO Rosneft, OAO Tatneft, OJSC Surgutneftegas, LLC Russneft.

Asymmetric cuffs have the following parameters:

1. The angle of the plane of the inner shoulder of the lower cuff β is smaller than the angle of the plane of the inner shoulder of the upper cuff α, therefore, when the lower cuff acts on the upper cuff at point K of FIG. 2, the sealing edge of the inner shoulder of the upper cuff is pressed against the surface of the stem (pos. 2). In particular, for this size of asymmetric chevron cuffs, the optimal ratio is: α = 55 °, β = 45 °.

2. The plane angle of the outer cuff shoulder in the upper part is γ = 65 °; therefore, when the bag is compressed, the outer cuff shoulders do not touch and nothing prevents the lower cuff from affecting the upper cuff at point K for a long time the package is in operation.

The self-sealing effect occurs in the package of asymmetric chevron cuffs as follows.

With a slight preload of the package (Figure 2) with a force F min = 2 ÷ 3 kg of a compression nut (not shown) from the effort of the hand (without using the handles), the lower cuff, leaning with its shoulders on the support sleeve (item 3,), is pressed against the surface of the stem (pos. 2), in the contact zone T, a frictional force arises, which drags the lower cuff when the rod moves, which acts at the point K on the inner shoulder of the upper cuff, instantly shifts all the upper cuffs and each upper cuff, acting on the point K, compresses the sealing lip next upper cuff to the surface STI rod. The purpose of the upper pressure sleeve (key 4) is to limit the movement of the cuff package following the moving stem.

Since the tightness in the contact area of the sealing edges of the inner shoulder of the asymmetric chevron cuffs with the stem surface occurs without the need for axial compression of the cuff pack with great force, but only due to the friction force of the cuff material on the surface of the polished stem, in this case the friction force is minimal and is determined by the coefficient friction, in particular the coefficient of friction of polyurethane on polished steel, which is one of the lowest among the materials used for the manufacture of chevron cuffs. Pilot tests over 150 days showed that tightness at a well fluid pressure of 1 ÷ 2 MPa is ensured with a freely rotating (not clamped) compression nut of the wellhead seal only due to self-sealing of a package of asymmetric chevron cuffs. Heating of the rod surface is not observed even with dry friction (in the absence of the borehole fluid at the wellhead), which indicates a minimum friction force in the contact area of the sealing lips of the cuffs with the rod surface.

Due to the difference in angles, annular cavities A are formed between the outer shoulders of the lower and upper cuffs, which are filled with liquid lubricant during assembly of the package, which serves to lubricate the surfaces of the cuffs for better sliding on the contacting surfaces.

Information sources

1. GOST 22704-77.

Claims (1)

A self-sealing pack of asymmetric chevron cuffs, consisting of at least two cuffs installed in an interference fit, a support and pressure sleeve, characterized in that, due to the asymmetry of the inner and outer shoulders of the cuffs, the outer shoulders of the cuffs do not touch, without interfering with the influence of the inner shoulders of adjacent cuffs on each other, leading to the occurrence of a self-sealing effect due to the difference in the angles of the surfaces of the inner shoulders of the cuffs in contact and sealing the moving polished rod with a minimum frictional force without the need for axial compression of the package with high force.

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