RU2120537C1 - Tubing centralizer-insulator - Google Patents

Abstract

FIELD: oil producing industry; may be used in wells with wax-hydrate accumulations on walls of tubing which are prevented or removed by direct (conductive) electric heating of tubing. SUBSTANCE: tubing centralizer-insulator assembly has body formed by segments made with internal longitudinal hole. Segments are joined at edges along length of centralizer-insulator by means of splined joint and fixed by studs. Body is made with eccentricity with respect to tubing. Center of circumscribed circle of internal geometric holes of segments coincides with center of circumscribed circle round outer sizes of segments. At ends, segments are made with beads and internal cylindrical surface whose diameter corresponds to tube internal diameter and diameter of internal cylindrical surface of segments corresponds to external diameter of coupling. The claimed invention is provided concentric arrangement of conducting members: internal conducting member of tubing with electric heating cable relative to external conducting member tubing. EFFECT: improved electric insulating properties between conducting members. 16 dwg

Description

 The invention relates to the oil industry and can be used in wells with paraffin-hydrate deposits on the walls of tubing (tubing), the prevention or elimination of which is carried out by direct (conductive) electric heating of the tubing string, regardless of the method of production, for example, using submersible centrifugal electric pumps (ESP), in a fountain way, using sucker rod pumps and other methods.

 A known centralizer-insulator for electrical insulation of the tubing string from the production string when electric current passes through them (see P.P. Galonsky "Paraffin control in oil production", Gostopizdat, 1955, p. 101, Fig. 65 and Fig. 67).

 One embodiment of the centralizer-insulator is an axisymmetric one-piece structure made of cylindrical textolite with a hole inside for the passage of tubing (see the same, Fig. 65).

 Another variant of the known centralizer-insulator is a detachable (on a threaded connection) axisymmetric structure made of cylindrical PCB with internal collars, worn on the tubing sleeve (see the same, Fig. 67).

 However, the design of such a centralizer-insulator does not provide electrical insulation of the tubing from the production string if the cable of the submersible centrifugal electric pump (ESP) is attached to the tubing, which in this case, touching the armor of the inner surface of the production string, violates the electrical insulation. In addition, due to damage to the cable armor, the operational reliability of the ESP cable is reduced.

 At the same time, these designs of the centralizer-insulator complicate their installation on tubing, since it is necessary to perform an additional operation to “pull” the centralizer-insulator through the pipe.

 The closest in technical essence, adopted by the authors for the prototype, is the centralizer-insulator of the tubing string according to US patent N 4266578.

 The centralizer-insulator is an axisymmetric detachable structure including a housing formed by segments made with an internal longitudinal hole. The segments are fixed to each other by means of a spline connection along the edges of the segments, in the body of the teeth of which through holes are made with the possibility of combining them and fixing them with studs. The segments on the one hand are connected by a fixed pin with the possibility of disclosing the segments and with their subsequent coverage of the tubing body. After crimping the pipe body and connecting the teeth from the other edge of the segments, a removable pin made in the form of a wedge-shaped metal rod is inserted into the holes of the teeth. This form of the rod provides a tight compression of the tubing body, preventing the centralizer from moving along the pipe during the round-trip operations (STR) of the tubing string in the well.

 The segments of the centralizer-insulator body are made of a metal frame rubberized with rubber.

 The main disadvantage of the known design is the following.

 This design of the centralizer-insulator, when used in wells during production with the help of the ESP, provides the clamping of the ESP cable only along the pipe body. At the junction of the tubing, the cable is located between the sleeve connection of the tubing string and the production string. Since the inner surface of the production casing has various protrusions, irregularities (especially in the sleeve joints of the production casing pipes) during tripping operations of the tubing often violates the cable armor.

 In addition, the use of a centralizer-insulator with a metal frame gummed with rubber also leads to a violation of the insulating properties of the insulator due to the rapid wear of the rubber shell during the STR.

 Thus, along the length of the tubing, an electrical contact is often formed between the tubing string, the ESP electric cable and the production string.

 To prevent paraffin-hydrate deposits or their elimination, electrical voltage is supplied to the wellhead to the tubing string and production string, isolated by centralizer-insulators, from each other. The electrical contact between the tubing string, the ETsN cable and the production string resulting from the violation of the integrity of the centralizer-insulator and the armor of the cable during tripping operations leads to the occurrence of welding currents at the point of contact and, as a result, to the failure of the ETsN cable and installation of electric heating in general.

 It should also be noted that the eccentric location of the ESP cable in a known design relative to the tubing axis and its approach to the production string further aggravates the situation, given the directional design of most modern wells.

 The present invention is to create a design of a centralizer-insulator of the tubing string, providing reliable electrical protection of the internal conductive elements, as well as protecting them from mechanical damage during tripping operations in the most vulnerable part of the tubing - the coupling connection, regardless of the method of operation of the wells: using submersible centrifugal electric pumps (ESP), using sucker-rod pumps, fountain method or others.

 The essence of the claimed invention is as follows.

 The centralizer-insulator of the tubing string assembly has a closed tubular shape and includes a housing formed by segments made with an internal longitudinal hole. Segments along the edges along the length of the centralizer-insulator are fixed to each other by means of a spline connection. Through holes in the teeth of the splined joint are made through holes with the possibility of combining them and fixing them with studs.

The distinctive features of the claimed centralizer-insulator of the tubing string are as follows: the casing is made with eccentricity relative to the axis of the tubing, while the center of the circumscribed circle of the inner geometric hole of the segments is aligned with the center of the circumscribed circle around the outer geometric size of the segments. At the ends, the segments are made with collars with an inner cylindrical surface, the diameter of which corresponds to the outer diameter of the pipe, and the diameter of the inner cylindrical surface of the housing segments corresponds to the outer diameter of the coupling, while the eccentricity is determined by the formula
e = k / 2,
Where
e is the magnitude of the eccentricity between the axis of the tubing and the center of the circumscribed circles of the internal geometric hole of the body and around the external geometric size of the body, m;
k - the maximum size of the conductive elements adjacent to the tubing along the radius of the described circles, m

 The inventive design of the centralizer-insulator of the tubing string leads to a concentric arrangement of the conductive elements, that is, such an arrangement of the internal electrically conductive element relative to the outer - production casing is provided, in which the outer surface of the internal conductive elements is equally spaced from the inner surface of the production string. This ensures equal electrical conductivity (electrical resistance) of the gap, which improves the electrical insulation properties between the two conductive elements, while the tubing coupling is a limiter of freedom of movement of the centralizer-insulator.

 The invention is illustrated by the following drawings.

 In FIG. 1 shows a variant of a two-segment centralizer - insulator assembly, top view.

 In FIG. 2 shows a variant of a two-segment centralizer-insulator assembly, side view.

 Figure 3 presents the stud for fixing the segments.

 Figure 4 presents a side view of segment 1.

 In FIG. 5 is a top view of segment 1.

 FIG. 6 is a section AA through the depression of the spline connection of the segment in FIG. 4.

 In Fig.7 is a section bB on the tooth splined connection of the segment in Fig.4.

 On Fig presents a side view of a segment, for example, with a groove for a conductive element, for example, a flat cable ESP.

 In FIG. 9 shows a top view of a segment, for example, with a groove for a conductive element, for example, an ESP flat cable.

 In FIG. 10 is a section BB of a tooth for a spline connection of a segment with a groove for a conductive element in FIG. eight.

 In Fig.11 - section GG on the cavity of the spline connection of the segment with the groove for the conductive element in Fig.8.

 In FIG. 12 is a variant of mounting a centralizer-insulator on a tubing coupling with a conductive element, for example, an ESP flat cable.

 In FIG. 13 is an embodiment of mounting a centralizer-insulator on a tubing coupling with a conductive element, for example, an ESP round cable.

 In FIG. 14 is an embodiment of mounting a centralizer-insulator on a tubing coupling with conductive elements, for example, an ESP flat cable and communication cables.

 In FIG. 15 shows an embodiment of a three-segment centralizer-insulator assembly, a top view.

 In FIG. 16 shows an embodiment of a four-segment centralizer-insulator assembly, top view.

 The body of the centralizer-insulator (see figure 1) includes segments 1 and 2, interconnected by means of a spline connection 3 along the edges of the segments (see figure 2). In the body of the teeth 4 of the spline connection 3, through holes 5 are made (see Figs. 2, 4, 5, 9, 10) with the possibility of combining them and fixing them with studs 6.

 The height of the tooth 4 and the depth of the cavity 7 of the spline connection on the mating segments 1, 2 (see Fig. 4, 8) provide the installation of connecting studs for radial movement of the segments relative to each other in order to open the centralizer-insulator for installation on the tubing string.

 The studs connecting the segments together (see Fig. 3) are, for example, an axis with a collet tip 8 at one end and a travel stop 9 at the other end.

 At the ends, the housing segments are made with collars 10 (see Fig. 1, 2, 4) for abutment against the ends of the coupling 11 (see Fig. 12-14) with an inner cylindrical surface 12 (see Fig. 2), the diameter of which corresponds to the diameter of the tubing 13, and tubing covering the body with a uniform gap (interference fit) over the entire surface of the pipe. The diameter of the inner cylindrical surface 14 (see Fig. 2) of the centralizer-insulator housing segments corresponds to the outer diameter of the coupling 11 of the tubing for fitting onto the coupling, with a uniform clearance (tightness) over the entire surface of the coupling.

 The height of the shoulder 10 is performed necessary to ensure the strength properties of the centralizer-insulator during the STR, impacts on the protrusions and friction on the production string.

 The assembled segments give the centralizer-insulator a closed tubular shape with a length that allows landing on the tubing coupling. The inner longitudinal hole of the cylindrical-shaped segments passes, for example, into the groove 15 (see FIGS. 1, 12) for laying and fixing the conductive elements, for example, the power cable ESP 16 on the body of the tubing string.

 This design of the centralizer-insulator guarantees a hard fit on the sleeve connection of the tubing string, without axial and radial movements of the centralizer-insulator relative to the tubing string.

The body of the centralizer-insulator is made with an eccentricity relative to the axis of the tubing string, and the center of the body is the center of the circumscribed circle with the radius (R _in ) of the internal geometric hole of the housing and it is aligned with the center of the circumscribed circle with a radius (R _n ) around the external geometric size case, while the amount of eccentricity of the body is determined by the formula
e = k / 2,
Where
e is the magnitude of the eccentricity between the axis of the tubing string and the center of the circumscribed circles of the internal geometric opening of the housing and around the external dimension of the housing, m;
k - the maximum size of the conductive elements adjacent to the tubing along the radius of the described circles, m

 Such a design of the centralizer-insulator provides an eccentric arrangement of the tubing string relative to the production string and a concentric arrangement of the tubing string with the ESP cable relative to the production string along the described circles.

 Installation sequence.

 The body of the centralizer-insulator, for example, by a longitudinal groove 15 (see Fig. 12) is put on a conductive element, for example, on an ETsN cable 16, is mounted on the sleeve 11 so that the upper and lower shoulders 10 of the housing cover the sleeve, are fixed on it, and the inner surfaces 14, 12 of the housing (the bodies of the segments and collars) laid respectively on the outer cylindrical surfaces of the coupling and pipe. Next, the segments, previously connected to each other on one edge of the segments by a pin 6, are deployed and laid on the sleeve 11. In this case, the upper and lower shoulders 10 of the segments cover the ends of the coupling and the inner surfaces of the shoulders abut against the ends of the coupling. The splined connection from the other edge of the segments is closed and fixed with a stud 6.

 The centralizer-insulator installed on the tubing coupling of the tubing string in this way presses the cable to the tubing string and protects the tubing string and the ESP cable from touching the production string, while maintaining a constant uniform clearance between the tubing string and the cable and the production string. This provides electrical isolation of the tubing string and the ESP cable from the production string, protecting the cable and tubing string from mechanical damage during tripping.

 The design of the centralizer-insulator ensures its implementation by casting, for example, of polyamide.

 The design of the proposed centralizer-insulator allows the tubing string to be oriented adequately to the azimuth and angle of inclination of the well structure (production string), which is important for installation in directional wells.

 To facilitate the installation of the centralizer-insulator on the tubing string, its body can be made three-segment (see Fig. 15) or four-segment (see Fig. 16).

 The specified design of the centralizer-insulator can be used for any methods of operating wells, while in the internal longitudinal hole, for example, with a groove, both ESP cable and communication cables or only communication cables for conducting well and reservoir studies can be laid. In the absence of power cables and communication cables, for example, during gushing operation or operation of a sucker-rod pump installations, if there is no need to study wells, formations and operation of the installations k = 0 and e = k / 2 = 0.

 An example of a specific implementation.

The design dimensions of the centralizer-insulator during the operation of the wells with an ESP unit with a cable KPBP 3x16 for production casing 146 mm and tubing string 73 mm:
the outer size of the centralizer-insulator is 122 mm (0.122 m);
internal size for the tubing sleeve - 89 mm (0.089 m);
groove depth = k = 14 mm (0.014 m);
groove width - 42 mm (0.042 m).

 At the same time, the guaranteed gap between the tubing string with the cable (conductive element) and the production string is 9.5 mm (0.0095 m).

 Tests of centralizer-insulators at all real loads in the production casing showed high reliability both from the point of view of mechanical protection of the conductive element, for example, cable and tubing string elements, and high electrical protection of the tubing string with a conductive element.

Claims (1)

The centralizer-insulator of the tubing string, including a housing formed by segments made with an internal longitudinal hole, fixed to each other by means of a spline connection along the edges of the segments, through holes are made in the teeth of the teeth with the possibility of combining them and fixing them with studs, characterized in that the housing is made with an eccentricity relative to the axis of the tubing, and the center of the described circumference of the inner geometric hole of the housing is aligned with the center of op ik- around the outer circumference of the geometric body sized for housing the ends of the segments formed with collar with an inner cylindrical surface whose diameter corresponds to the diameter of the tubing and the diameter of the inner cylindrical surface of the housing segments corresponds to the outer diameter of the sleeve, wherein the magnitude of the eccentricity body is determined by the formula
e = k / 2,
where e is the magnitude of the eccentricity between the axis of the tubing and the center of the circumscribed circles of the internal geometric holes of the housing and around the outer size of the housing, m;
k - the maximum size of the conductive elements adjacent to the tubing along the radius of the described circles, m

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