RU184435U9 - Well-tightened pipe for threaded joints - Google Patents

Abstract

The invention relates to threaded oil and gas production pipes, namely to casing pipes with highly tight threaded joints intended for fastening the borehole wall of a drilled well, as well as to tubing pipes with highly tight threaded joints intended for oil, gas, gas condensate or injection into underground formations of any liquids, gases, or combinations thereof. A pipe for wells with a high-tight threaded connection with tapered threaded surfaces with a trapezoidal thread, with an end and radial sealing units, characterized in that the radial sealing element in the threaded connection on one of the elements (pipe or sleeve) is made in the form of successive sections forming at force screwing of the threaded connection at least two contacting surface "sphere-cone" and representing on the outer or inner element of the pipe sequentially located linear (conical) and curvilinear (toroidal or spherical) sections with linear (conical) sections corresponding to them or a section on the mating pipe element with a taper from less than 1: 6 to a cylindrical surface so that the centers of these curved (toroidal or spherical) ) the elements are located relative to the end of the tube element at a distance of no more than 2/3 of the entire length of the radial sealing assembly for the first curved element and for the second curved element - and the distance calculated on the basis of the conditions for ensuring the operation of the pipe in the well with various combined constant contact loads and the first and second spherical sections of the seal and 100% efficiency of the threaded joint in compression and tension. 5 ill.

Description

The invention relates to threaded oil and gas production pipes, namely to casing pipes with highly tight threaded joints intended for fastening the borehole wall of a drilled well, as well as to tubing pipes with highly tight threaded joints intended for oil, gas, gas condensate or injection into underground layers of any liquids.

First of all, the utility model relates to pipes used in the development of oil and gas fields, to which high demands are placed on the strength, reliability and tightness of the threaded joint in various operating conditions, for example, such as:

- operation at bending loads up to 100% in equivalent axial loads along the pipe body;

- operation under the action of combined loads (compression-tension and internal or external pressure with bending), sometimes with their cyclical change, which can occur both when the pipe is lowered into the well, and during its operation;

- high torsion moments of the pipe string, which occurs when the pipe string is lowered into a directional and horizontal well or when cementing with rotation of the string.

In such conditions, it is generally considered advisable to use casing and tubing with high-tight threaded joints having metal-metal seals and thrust end elements, since It is the threaded joint that is most at risk of damage when lowering the pipe in the well. In this case, the high operational properties of high-tight threaded joints reduce the risk of emergency situations in the well, accompanied by large economic losses and environmental problems.

At present, casing and tubing with threaded connections with trapezoidal conical threads and sealing surfaces of the mating elements on the male and female mating element (nipple and coupling /) are used for the construction of wells with vertically directed (inclined) geometry of the bore or with horizontal sections of the bore. coupling end, respectively) - both radial and end sealing surfaces. In this case, the end surfaces additionally serve to create preliminary axial stresses at the stage of axial attachment of the threaded connection, compressive stresses are created for the nipple part, and tensile stresses are created for the mating (coupling) part.

For example, in the technical solution described in the patent for utility model RU 116952, the authors propose a threaded connection with a “cone-cone” seal with an increased taper of 1:10, while the sealing surfaces pass through the fillet into end contact surfaces, as a result, the seal is located at the end of the tube element, and the technical solution according to the patent for invention RU 2310058 offers a threaded connection with a sphere-cone seal, with a conical section with a taper of 1:10 located on the coupling lemente, and pin-element compound - spherical radial seal portion smoothly passing into the abutment end surface. These proposed technical solutions have advantages only in certain operating conditions, for example, the authors of RU 2310058 justifiably suggest increasing the operational reliability of the connection by providing an increase in the contacting areas of the ends to increase the torque of make-up while maintaining contact stresses within the elastic deformation. Nevertheless, a simultaneous increase in tightness is minimal when exposed to large bending moments in combination with tensile loads and external pressure of the medium due to the presence of only one sealing surface of the mating elements, in case of loss of contact in which the tightness of the connection is lost. Similarly, for technical solution RU 116952, in which the geometric characteristics of the connection are slightly different from RU 2310058.

It should be noted that the joints with the metal - metal pipe seal work as follows: during assembly of the joint, the sealing surfaces experience radial elastic or plastic deformations, as a result of which a contact area is created with large contact stresses, which provides the necessary tightness. The tightness properties of the joint are ensured by the length of the contact occurring, by the nature of the contacting surfaces - in fact by the shape of these surfaces.

For example, it is known from the prior art that the high-tight threaded joints developed in the 1980-1990s provided 100% tensile and internal pressure efficiency, but had low compression and external pressure performance. The reasons for the low compression resistance are certain structural limitations - the thickness of the so-called nozzle (end section), where the sealing surfaces of the mating elements were located, most often amounted to no more than 50-60% of the pipe wall thickness. In this case, when a compressive load is applied to the threaded joint, it is almost completely transferred to the end surface of the nozzle (end section), which leads to plastic deformations, displacement of the nozzle (end section) of the nipple to the pipe axis and opening of the metal-metal seal, i.e. . there is a loss of tightness of the threaded connection.

For example, the method of increasing the resistance to external pressure and the compression resistance of the threaded connection by increasing the radial stiffness of the nipple at the location of the seal and the concomitant increase in the radial size of the thrust end is technically justified in solution EA 008078. In accordance with this invention, the seal is located near the threaded part, and between a seal and a persistent end is a nose (end section) of a special shape, between the outer surface of which and the coupling there is Azor formed by a special coupling bore. But with all the advantages, the authors of the indicated technical solution show that even with a large thickness of the spout (end section) with the simultaneous application of a strong compression force and external pressure, depressurization is possible.

Technical solutions are also known, for example, DE4446806, WO 2009/060729 or WO 2004/109173, in which the solution of the problem considered by the authors is carried out by moving the main sealing surfaces of the mating elements further from the end of the pipe. But from the literature data on the problem, it is known that in the case of a large distance between the seal and the axial stop (shoulder), it is necessary to take into account the possibility of elastic bending of the nose (end section) of the nipple in the non-contact zone between the seal and the shoulder. In this case, the complex deformation of the nozzle (end section) can lead to the fact that the contact pressure in the seal can both increase and decrease, which will lead to the appearance of scoring in the first case, and to the loss of tightness in the second case.

To overcome this phenomenon, the authors of the technical solutions described in DE 4446806 and WO 2009/060729 add an additional element between the main seal and the thrust end that restricts the outward movement of the nipple nose (end section) and ensures centering and stabilization of the main seal under combined loads. But in all these cases, the authors indicate that the functions of this additional element consist only in centering the joint during screwing and stabilization of the spout of the end portion under loads.

Thus, various researchers have attempted to create such a geometric solution to the sealing surfaces of the mating elements that will maintain tightness under various load cases - but there is such a combination of loads when the auxiliary elements introduced by specialists become “harmful” to the threaded connection.

The technical solution is a pipe with a tight threaded connection of oilfield pipes according to the patent RU 2310058 adopted as the closest analogue (prototype) of the claimed utility model.

Common features of this prototype with the claimed technical solution "Pipe for wells: are the following features: tapered threaded surfaces of male and female elements with a trapezoidal thread and a radial sealing assembly formed by forcefully screwing a threaded connection and representing an end threadless section with mating sealing surfaces, which has a shoulder on the female member and an end face on the male member abutting said shoulder.

The objective of the claimed utility model is to create a pipe for wells with a threaded connection, which would have the highest possible sealing characteristics and increased reliability for the widest range of operating loads, including bending, compressive, combined and cyclic loads while maintaining performance after repeated assembly-disassembly operations for both casing and tubing.

The technical result provided by the claimed utility model consists in creating a pipe with a threaded joint having a high tightness margin in the metal-metal seal under the effect of significant multidirectional loads on the threaded joint (tensile, compressed and bent pipes, internal in the pipe and external in well / annulus gas pressure), capable of withstanding multiple make-unscrew cycles in the absence or minimization of metal scuffing on the sealing surfaces of yagaemyh elements and thread.

The essence of the proposed utility model is as follows.

A pipe for wells with a high-tight threaded connection includes tapered threaded surfaces of the male and female elements with a trapezoidal thread and a radial sealing assembly formed by forcefully screwing the threaded connection and representing an end threadless section with mating sealing surfaces that has a shoulder on the female element and the end an element abutting said shoulder. What is new is that the mating sealing surface of the enclosing element is made tapered with a taper of not more than 1: 6, and the response of the indicated mating surface — the sealing surface of the covered element — is made with two successive convex toroidal sections, while the center of the circumference of the toroidal section located at the end the covered element is spaced from this end face at a distance of no more than 2/3 of the length of the end threadless portion of the radial sealing assembly.

Before describing the technical parameters of the proposed technical solution, we will make some explanations and apply some concepts that are well-established among designers and technologists of threaded joints:

- “sphere” - is used to explain the profile of the sealing surfaces of the mating elements, the cross section of which is an arc (of any radius), while on the body of revolution (on the pipe or sleeve / socket end-socket, for example), this element is actually a surface close to a toroid;

- “shoulder” is a mechanical seal with a protrusion (collar), called from the English “shoulder”.

The use of such specific concepts will allow specialists in the field of threaded joints under consideration to clearly understand what is at stake.

The technical result of the utility model claimed by the authors is achieved through the manufacture of tubing and casing with a highly tight threaded connection with a tapered trapezoidal thread with end and radial sealing units. In this case, the radial sealing surfaces of the mating elements are made in the form of a contacting pair of successively arranged (toroidal surfaces - for one element of the pair (male element) and conical surfaces with a taper of not more than 1: 6. for the second element (female element); these pairs of surfaces form when force screwing of a threaded surface of the "sphere-cone" type.

An additional very important element is the distance at which the toroidal sealing surfaces are located relative to the rest of the connection elements. Based on the results of calculations by the finite element method and research / testing of samples of the connection, the authors propose to establish certain patterns - the centers of these spherical elements (in the longitudinal section of the connection are the centers of the circles that describe these surfaces) should be located relative to the end of the pipe element:

for the first spherical element at a distance of not more than 2/3 of the entire length of the end threadless portion of the radial sealing assembly.

- for the second spherical element at a distance calculated on the basis of the conditions for providing the pipe during operation in the well with various combined loads of constant contact and for the first and second spherical sections of the seal and ensuring, as a result, 100% threaded joint operation for compression and tension. However, this feature is not considered as an essential feature of the proposed utility model.

The essence of this utility model and the possibility of achieving the claimed technical result become clear thanks to the description of an example of its execution shown using the accompanying figures:

figure 1 is a schematic representation of a threaded connection in isometry with a local section (a special case is a coupling connection; the coupling is a female element);

figure 2a - schematically shows the main view of the threaded connection in section (a special case is the coupling connection; the coupling is a female element);

Figures 2b and 2d show a schematic representation of a part of a pipe thread element (nipple) in longitudinal section, indicating the radii of the toroidal sealing surfaces and the distances between their centers: Fig. 2b is an embodiment with 2 (two) toroidal sealing surfaces, FIG. 2d - variant with 3 (three) toroidal surfaces;

in FIG. 2c is a schematic representation of a portion of a sleeve member in longitudinal section.

According to the proposals of the authors, a pipe with a high-tight threaded connection in the part of the threaded connection (Figs. 1 and 2a) includes an internal male (1) and external female (2) mating elements with conical surfaces on which the threaded sections are made, and a radial sealing (sealing ) node (3).

It should be noted that, despite the fact that, as an example, the authors illustrate the description with a male threaded connection, all technical solutions are equivalent for a non-coupled connection, i.e. when two pipes are connected not by means of a separate coupling, but in the pipe design it is provided that one end of the pipe is made in the form of a traditional nipple with an external thread, and the opposite end of the pipe is in the form of a socket, i.e. - This is the sleeve end of the pipe.

In accordance with the claimed utility model, in the most optimal case, the sealing assembly (3) on the pipe (Fig. 2b, for a female threaded joint) includes radial sealing surfaces located on the inner (1) male mating element in the form of conical (linear) consecutive and toroidal (curvilinear) sections (Fig. 2b, pos. 4 and 5), and on the coupling element the response section to it is made with a taper of not more than 1: 6 (Fig. 2c).

Such an arrangement - the curved sections on the nipple, and the conical surface on the coupling, the most optimal from the production point of view - it is easier to control the shape and dimensions of the spherical (curved) sections on the external thread (pipe) than on the internal one.

In FIG. 2b shows the most optimal variant from the point of view of ease of manufacture and control of the nipple, when the number of (toroidal) sections (poses 4 and 5) does not exceed 2 (two). In this case, the calculation of geometric parameters (for example, diameters, circle centers and relative positions) of these elements is simpler, and manufacturing under industrial conditions requires less effort (from the point of view of cutting and control). But it should be noted that the authors admit that the number of toroidal sections on the radial sealing surface can be more than two. For example, it is technically possible to arrange another spherical section (Fig. 2d, item 9), which, in addition to the additional sealing functions, will perform its main other function - centering the nipple part (pipe) relative to the coupling part (for example, the coupling) at the initial make-up stage, when deviations from the alignment of the elements can lead to scoring on mating surfaces or damage to the first turns of the thread and, accordingly, a decrease in operational reliability. But the authors consider this option as a possible option because of the difficulty in manufacturing at the current stage of development of threaded equipment - to ensure the required connection characteristics during operation, all three (toroidal) elements must be performed with very high accuracy (± 0.01 mm against ± 0 , 03-0.05 mm for the case with two elements). In industrial conditions, in-line production of products to ensure such accuracy at this stage of development of industrial equipment is impossible - only in the conditions of piece production (for example, in experimental production), which is not yet acceptable for the production of casing and tubing in large pipe plants, which per hour can produce up to several hundred products (depending on size). In the future, with the development of rifled machines, this problem can be solved.

Considering the following construction as an example, it should be noted that the distance (pos. 6, Fig. 2b) from the pipe end to the spherical element (pos. 4, Fig. 2b) with radius R1 is no more than 2/3 of the entire length (pos. 8, Fig. 2b, i.e., this is the distance to the thread) of the radial sealing assembly, and to the second (distance pos. 6 + distance pos. 7, Fig. 2b) a spherical element with radius R2 (pos. 5, Fig. 2b) is calculated experimentally from the condition of providing during operation of the pipe in the well with combined constant contact loads and in the first and second spherical sections (items 4 and 5, Fig. 2b), and at the same time providing 100% efficiency of the threaded connection for compression and tension. The case with another additional toroidal element is shown in FIG. 2g The sealing surfaces of the mating elements (pos. 9, Fig. 2d) in this case will perform the main technical task - centering (stabilization) of the joint when making up, which will allow for the element in pos. 4 leave only the main task - sealing, excluding for him the problem of centering (stabilization) of the connection when making up. In this embodiment, the distance for the elements in pos. 4 and pos. 5 (Fig. 2b) will be calculated according to the above principle, and the element according to pos. 9 will be located as close as possible to the end of the pipe to fulfill its main role - it will first come into contact with the corresponding sealing surfaces of the mating elements of the coupling part of the connection and carry out centering.

In order to further avoid confusion, the authors propose to further consider a design with two sealing spheres and the first to consider a seal located on the side of the thrust end, i.e. closer to the end of the pipe (pos. 4, Fig. 2b), and the second is the seal located on the thread side (pos. 5, Fig. 2b).

The distances proposed by the authors from the end of the pipe to the center of the first spherical element (pos. 6, Fig. 2b), as well as the distances between these spherical elements (pos. 7, Fig. 2b) were proposed by the authors as a result of verification strength calculations using finite element and full-scale methods tests of samples of threaded joints on test benches: the fulfillment of this ratio limits the negative effect of “squeezing” the seal when exposed to adverse combinations of loads, which allows you to create a threaded connection PAS "Premium" with increased tightness and reliability characteristics.

For example, technical solutions according to DE 4446806 provide that the second reference point (i.e., the second sealing surfaces of the mating elements) provides additional contact between the surface of the nipple and the mating surface of the coupling, which allows a fuller use of the radial stiffness of the long nipple. However, for a certain type of load (for example, external pressure combined with bending, it can lead to the formation of a gap or irreversible plastic deformations at the second reference point, i.e., to create conditions for loss of tightness. All this takes place due to the chosen technical essence this additional sealing element (closest to the end of the pipe).

The authors of the proposed utility model as a result of calculations and experimental work with images of a threaded connection found a way to solve this problem - to create such a pipe with a sealing unit containing two spherical cones spaced apart in the axial direction, the first of which is located on the side of the thrust end, the second sides of the threaded part, characterized in that both seals maintain tightness throughout the VME circle of repeated combined loads.

When a group of at least two seals is located on the nipple, in each of which a certain geometric interference is created, an increase in the joint tightness is achieved due to synergy, i.e. the effect of seals on each other. The fulfillment of these conditions is ensured by the correct selection of the radii of the sealing surfaces and the geometric position of each element relative to the end of the pipe and relative to each other.

The calculations of the authors of the proposed technical solution show that the preferred distance from the point (center of the circumference of the section) of the first seal to the end of the nose (end section) of the nipple is no more than 2/3 of its length, the nose. With a greater distance from the point (center of the circumference of the cross section) of the first seal to the end face of the nipple end portion of the nipple, the risk is significantly increased that due to the creation of a pressing effect due to the shoulder (protrusion) during axial attachment, the second (far from the end) sealing surfaces will be pressed mating elements, and at very large distances, the first spherical element can also be squeezed out. In this case, the tightness margin in the second seal is accordingly reduced.

For the second seal, the choice of the distance from the point (center of the circumference of the section) to the end of the nose of the end section of the nipple is determined from the view that the maximum contact stress in the seal is 100-160% of the yield strength of the nipple material. So, if the maximum contact stresses are less than 100% fluidity, the reliability of the joint in terms of tightness is reduced, and if the maximum contact stresses are exceeded more than 160%, plastic deformations in the contact area may occur, which increases the risk of scoring during make-up.

The pipe proposed by the authors was manufactured industrially using conventional metalworking technologies used in the production of tubing and casing pipes, including using various material pipe designs - pipe samples were made with the proposed threaded joint from ordinary carbon steel (steel of the strength group Q125 according to API 5CT), and also samples of pipes were made of high-chromium steel 13Cr-P1 10L.

Pipe for wells in accordance with the claimed utility model can be used for various pipe sizes and strength groups of the material. When changing the size or strength group, it is necessary to choose the correct geometric parameters that affect the performance of the connection. A specialist with relevant skills in the theory of elasticity and strength, as well as the skills to design and calculate thick-walled and thin-walled shells working under pressure, can select these parameters taking into account the described technical features of the threaded connection designed in accordance with the presented utility model.

Tests of the prototype according to the methods in accordance with the API 5C5 standard confirmed the influence of a set of essential features on the achieved technical result.

Claims (1)

A pipe for wells with a high-tight threaded connection, including tapered threaded surfaces of the male and female elements with a trapezoidal thread and a radial sealing assembly formed by forcefully screwing the threaded connection and representing an end threadless section with mating sealing surfaces that has a shoulder on the female element and male element abutting against said shoulder, characterized in that the mating sealing the surface of the enclosing element is conical with a taper of not more than 1: 6, and the response of the indicated mating surface — the sealing surface of the enclosed element — is made with two successive convex toroidal sections, while the center of the circumference of the toroidal section located at the end of the covered element is spaced from this end at a distance of no more than 2/3 of the length of the end threaded portion of the radial sealing assembly.

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