CN114961590A - Special screwed joint of casing pipe for unconventional oil gas horizontal well multistage fracturing - Google Patents

Abstract

The invention belongs to the technical field of screwed joints, and discloses a special screwed joint of a casing for unconventional oil-gas horizontal well multistage fracturing, which comprises an external screwed joint and an internal screwed joint which are connected in a coupling manner; the external thread joint comprises an external thread section, an external thread sealing section and an external thread shoulder section which are connected in sequence; the external thread sealing section comprises an external thread main sealing surface and an external thread sealing surface guide surface; the internal thread joint comprises an internal thread section, a tool withdrawal groove section, an internal thread sealing section and an internal thread shoulder section which are sequentially connected; the internal thread sealing section comprises a conical surface sealing surface and an arc sealing surface, the conical surface sealing surface is connected with the tool retracting groove section through an arc transition surface, and the arc sealing surface is connected with the internal thread shoulder section; the thread forms of the external thread section and the internal thread section are interchangeable with the API standard buttress thread form. The problem of the operating mode suitability of current API standard screw thread, semi-special screw thread and high-end special screw thread not enough is solved.

Description

A special threaded joint of casing for multi-stage fracturing of unconventional oil and gas horizontal wells

technical field

The invention belongs to the technical field of threaded joints, in particular to a special threaded joint for casings for multistage fracturing of unconventional oil and gas horizontal wells.

Background technique

Shale gas and shale oil are unconventional oil and gas resources. Shale gas is stored in the fractures and pores of organic-rich mud shale or high carbon mud shale in a free or adsorbed state. Shale oil is contained in pores and fractures of shale, tight carbonate or clastic rock adjacent layers and interlayers. This kind of oil and gas resources has no natural production capacity, so special production technologies such as horizontal wells and multi-stage fracturing must be used. In this way, the contact area between the wellbore and the reservoir is increased, and the oil and gas production crevice channels are artificially created, thereby obtaining industrial production. It is technically difficult and requires strict cost control. At present, the average length of horizontal well sections in shale oil and gas development exceeds 2,000 meters, and there are more than 20 multi-stage fracturing stages. The production casing of the horizontal well section is subjected to the rotating bending and tension-compression alternating loads during going downhole, the liquid high internal pressure cyclic load during fracturing, and the long-term gas low internal pressure during the production process. The special thread puts forward the requirements for the applicability of working conditions that take into account the economy. The economic requirements are mainly manifested in: easy processing, simple testing, and broad quality control. , fatigue resistance, high pressure liquid / low pressure gas sealing performance, etc. The selection process of casing threads for shale oil and gas development has undergone continuous exploration and tortuous development. In the early days, API standard threads were used for reference from North American experience. However, shale oil and gas in my country are buried deeper and have higher fracturing grades. API standard threads have tightness and compression resistance. On the basis of API standard thread, the semi-special thread with added shoulder is upgraded and adopted, but the large torque fluctuation range leads to the inability to guarantee the fatigue resistance, and the lack of the main sealing structure makes it impossible to meet the requirements High-pressure fracturing requirements; in recent years, in order to solve the above problems, high-end special threads with typical radial seal, cylindrical nose and shoulder structure are widely used, but they show the disadvantages of excessive sealing, insufficient compression resistance, and high cost. , which cannot meet the engineering needs of safe and efficient large-scale development of shale oil and gas.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells, which solves the problem of insufficient working conditions of existing API standard threads, semi-special threads and high-end special threads.

The present invention is achieved through the following technical solutions:

A special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells, comprising an external threaded joint and an internal threaded joint that can be connected by coupling;

The external thread joint includes an external thread section, an external thread sealing section and an external thread shoulder section which are connected in sequence; the external thread sealing section includes a main sealing surface of the external thread and a leading surface of the sealing surface of the external thread; the main sealing surface of the external thread and the sealing surface of the external thread The guide surfaces are arc surfaces;

The internal thread joint includes an internal thread section, a relief groove section, an internal thread sealing section and an internal thread shoulder section which are connected in sequence; the internal thread sealing section includes a conical sealing surface and an arc sealing surface, and the conical sealing surface transitions through the arc The surface is connected with the undercut section, and the arc sealing surface is connected with the internal thread shoulder section;

When the male threaded joint and the female threaded joint are engaged, the male threaded sealing section is in contact with the female threaded sealing section;

The thread profile of the external thread segment and the internal thread segment adopts the thread profile that can be interchanged with the API standard buttress profile.

Further, the shoulder surfaces of the internal thread shoulder segment and the external thread shoulder segment are both right-angled shoulder surfaces or negative-angled shoulder surfaces.

Further, the shoulder angle of the right-angled shoulder surface is 90° to the axial direction of the casing, and the shoulder angle of the negative-angle shoulder surface is -3° to the radial direction of the tube.

Further, the taper angle of the conical sealing surface is 10-25°, the axial length of the sealing surface of the inner thread sealing section is greater than or equal to 3.3mm, and the roughness is controlled to be 0.5-0.8um;

The radius of the arc sealing surface is 0.8 to 1.5 mm.

Further, the arc radius of the main sealing surface of the external thread is 30-80 mm, and the arc radius of the leading surface of the external thread sealing surface is 1-2 mm;

The axial length of the external thread sealing section is greater than or equal to 3.5mm, and the roughness is 0.5-0.8um.

Further, the undercut is used for tool retraction and storage of thread grease, and the axial length of the undercut is 1 to 1.5 times the thread pitch.

Further, the taper of the external thread segment is 1.59 mm in diameter increment per 25.4 mm of axial length, and the tooth crest and the tooth bottom of the external thread segment are parallel to the generatrix.

Further, the inner thread segment adopts the same taper as the outer thread segment;

Or the internal thread segment adopts a variable taper scheme, specifically:

Taking the mid-diameter point as the axial boundary, set up a circular arc transition section within the pitch range, with different taper tolerance zones, the side near the end face of the coupling is a larger taper section, and the side near the shoulder surface is a small taper The tooth crest and tooth base of the female thread segment are parallel to the generatrix.

Further, the larger taper section adopts a taper tolerance zone with a diameter incremental change range of -0.015 to +0.114mm per 25.4mm axial length;

The small taper section is set with a taper tolerance zone with a diameter incremental change range of -0.064 to +0.025mm per 25.4mm axial length.

Further, the increase range of the complete thread axial length of the external thread segment is 20-30 mm; the increase range of the pitch diameter of the inner thread segment is 0.1-0.2 mm.

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

The invention discloses a special threaded joint of casing for multi-stage fracturing of unconventional oil and gas horizontal wells. The sealing surface, shoulder and thread taper structure of the joint are designed, and different design parameter combinations are adopted according to the classification of working condition parameters. A low-cost strategy is used to address the full-cycle requirements of horizontal well fracturing conditions; the external threaded joint adopts the compact connection and smooth transition of the threaded section, the sealing section and the shoulder section, and the cylindrical nose end is omitted. The female threaded joint adopts the thread, seal and shoulder part corresponding to the external thread, and adopts the undercut groove to avoid the interference of the external thread screwing, the machining retraction, the stress dispersion and the storage of thread grease and other functions. It adopts the tooth shape that is interchangeable with the API standard trapezoidal tooth shape. The above design ensures the connection performance, sealing performance, screw-in positioning and other functions, and greatly saves the processing cost and maintenance cost; the internal thread sealing section includes the conical surface seal The sealing surface of the external thread includes the main sealing surface of the external thread and the leading surface of the external thread sealing surface; the sealing surface of the conical surface and the main sealing surface of the external thread adopt the metal-metal interference fit sealing structure of the arc-to-cone surface. , to achieve a normal distribution of contact pressure distribution; the arc-cone metal sealing surface structure keeps the contact point of the main seal at a distance from the shoulder, reducing the risk of mechanical bumps during the make-up process; greatly reducing the support of the seal to the negative-angle shoulder Depends on the function; the optimized taper of the external thread takes into account the sealing performance under the composite load of anti-galling and high tensile internal pressure; the sealing length is sufficient to ensure that the integral value of the sealing contact pressure over the contact width is higher than the leakage threshold; the reliability of the sealing structure There is no additional high requirement for surface roughness control; the optimized camber radius takes into account the matching of contact width and peak contact stress, and meets the high sealing performance under the premise of anti-galling.

Further, the internal thread and external thread shoulder sections can adopt right angles and low negative angles, reducing the dependence of the sealing structure on the shoulder support, making the main seal position away from the shoulder to reduce the risk of mechanical damage to the main seal and increasing the shoulder section. structural strength to improve the compression and torsion resistance of the threaded joint.

Further, the shoulder surfaces of the internal thread shoulder section and the external thread shoulder section adopt right-angled shoulders or negative-angled shoulders. The right-angled shoulders control the deformation of the nose end, reduce stress concentration, and maximize the anti-torsion capability of the thread. The lack of support for the sealing surface can be selectively compensated by the internal thread variable taper scheme; at the same time, according to the comprehensive consideration of working conditions and application and processing cost control, a low negative angle shoulder (-3°) can be selected. ), which is much lower than the shoulder angle of typical special threads (generally -10~-15°), which significantly improves the sealing performance on the basis of limited reduction of torsional resistance; right-angle and low-negative angle shoulders are easy to clean. By omitting the cylindrical nose structure of the external thread, the rigidity of the sealing structure of the external thread is increased; the stability of the sealing structure of the internal thread is increased by distributing the stress dispersion of the undercut groove. As a result, a full 90° right-angle shoulder structure is used to ensure high sealing and high compression resistance, and an optional -3° low negative angle shoulder is realized to achieve a reasonable match of high pressure sealing and compression resistance.

Further, the optimization of dimensions such as the length of the relief groove ensures the sufficient length of the threaded connection strength, and realizes functions such as avoiding screw-in interference of external threads, machining retraction, stress dispersion and storage of thread grease.

Further, the outer thread sealing surface adopts double arc surfaces, including the main sealing arc surface and the outer thread sealing surface guide surface; The rigidity of the sealing surface cooperates with the arc surface of the nose end of the internal thread to form the thread grease storage space of the sealing section.

Further, the external thread adopts a single taper, and the internal thread adopts the optional variable taper technology to realize the flexibility of the design, manufacture and use of the threaded joint. At the end of the externally threaded pipe with less rigidity, by slowing down the taper of the internal thread, the deformation of the nose end of the external thread after make-up is reduced, and the risk of galling is reduced, making up for the shortage of excessive deformation of the sealing surface without a cylindrical surface transition, and fully ensuring sufficient sealing Surface contact pressure; when the rigidity is relatively large, close to the disappearing end of the external thread, increase the taper of the internal thread to improve the torque of the thread part during the make-up process, and ensure the thread make-up in place and the ability to resist over-torsion. By selectively adopting the internal thread variable taper combination, a reasonable matching of torsion resistance and sealing performance is achieved. An economical sealing structure suitable for different internal pressure levels is formed by the change of the shoulder angle and the thread taper, which realizes the flexibility of the design and manufacture of the threaded joint. For different sealing and anti-torsion conditions, various combinations of cost and performance are provided.

Further, based on the API standard thread profile, the effective length of the complete profile is increased, the pitch diameter interference of the thread is reduced, and the flexible design is realized through the change of taper, which not only improves the applicability of multi-stage fracturing conditions in horizontal wells, It also realizes the requirements of processing versatility, operation interchangeability and manufacturing economy; the thread bearing area is increased by increasing the complete thread axial length of the external thread; the pitch diameter of the internal and external threads is optimized, considering the shoulder bearing 90 In the case of % total torque, the anti-galling performance is significantly improved by reducing the thread interference fit, which greatly reduces the risk that the final torque will not be made in place on site.

Description of drawings

Fig. 1 is the sectional structure schematic diagram of the special threaded joint of the present invention;

Fig. 2 is the schematic diagram of the special threaded joint right angle shoulder thread and sealing form of the present invention;

3 is a schematic diagram of the negative angle shoulder thread and sealing form of the special threaded joint of the present invention;

Fig. 4 is a schematic diagram of the inner thread segmented taper form of the special threaded joint of the present invention.

In the figure: 1 is the inner thread joint, 11 is the inner thread section, 12 is the undercut section, 13 is the inner thread sealing section, and 14 is the inner thread shoulder section;

131 is the conical sealing surface, 132 is the arc sealing surface;

14-1 is the right-angle shoulder surface of the internal thread shoulder section, and 14-2 is the negative angle shoulder surface of the internal thread shoulder section;

2 is the external thread joint, 21 is the external thread section, 22 is the external thread sealing section, 23 is the external thread shoulder section; 221 is the external thread main sealing surface, 222 is the external thread sealing surface guide surface;

23-1 is the right-angle shoulder surface of the external thread shoulder section, and 23-2 is the negative angle shoulder surface of the external thread shoulder section;

15 is the larger taper section, 16 is the arc transition section, and 17 is the slightly smaller taper section.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are to explain rather than limit the present invention.

As shown in FIG. 1 , the present invention discloses a special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells, including an external threaded joint 2 and an internal threaded joint 1 connected by a coupling; the external threaded joint 2 includes The external thread section 21, the external thread sealing section 22 and the external thread shoulder section 23 are connected in sequence; the external thread sealing section 22 includes the external thread main sealing surface 221 and the external thread sealing surface guide surface 222; the internal thread joint 1 includes sequentially connected The internal thread section 11, the undercut section 12, the internal thread sealing section 13 and the internal thread shoulder section 14; the internal thread sealing section 13 includes a conical sealing surface 131 and a circular arc sealing surface 132, and the conical sealing surface 131 passes through the circular arc The transition surface is connected with the undercut section 12, and the arc sealing surface 132 is connected with the internal thread shoulder section 14; type.

Both the female threaded joint 1 and the male threaded joint 2 are steel casing joints, the outer diameter of the male threaded joint 2 can be 139.7mm, the outer diameter of the female threaded joint 1 can be 160 mm, and the outer diameter of the female threaded joint 1 and the male threaded joint 2 can be 160 mm. Taper thread fit is adopted between the inner thread joints 1 and 2, and the metal interference sealing structure in the form of arc surface-cone surface is adopted for the inner threaded joint 1 and the outer threaded joint 2, and the right angle or low negative angle shoulder structure is adopted for the inner threaded joint 1 and the outer threaded joint 2.

The external thread main sealing surface 221 and the external thread sealing surface guide surface 222 are arc surfaces, the arc radius of the external thread main sealing surface 221 is 30-80 mm, and the arc radius of the external thread sealing surface guide surface 222 is 1-2 mm.

Specifically, starting from the end face of the external thread of the pipe, a radial arc surface sealing surface consisting of a small radius arc (radius 1-2 mm) and a large radius arc (radius 30-80 mm) is constructed, and the small radius arc is the outer The thread sealing surface guide surface 222, the large radius arc is the main sealing surface 221 of the external thread, and the main sealing surface 221 of the external thread naturally disappears in the thread part. The external thread sealing section 22 is completed by a simple nose chamfering process, ensuring that the axial length of the external thread sealing section 22 is not less than 3.5mm, and the roughness is controlled to be 0.5-0.8um.

The external thread sealing section 22 adopts a small radius arc (radius 1-2mm) as the guide surface for making up, dispersing the contact pressure when the sealing surface starts to contact during the making up process, greatly reducing the risk of sticking of the sealing surface; the external thread sealing section 22 adopts The large radius arc (radius 30-80mm) is used as the main sealing surface of the radial arc surface, which increases the sealing contact width and improves the robustness of the sealing structure.

The inner thread sealing section 13 includes a conical sealing surface 131 and a circular arc sealing surface 132, the taper angle of the conical sealing surface 131 is 10-25°, and the radius of the circular arc sealing surface 132 is 0.8-1.5 mm. Specifically, starting from the shoulder surface of the inner thread of the coupling, a radial conical sealing surface 131 composed of a small radius arc (0.8-1.5 mm) and a tapered surface (taper angle 10-25°) is constructed. The angle disappears in the thread relief groove, the axial length of the sealing surface is not less than 3.3mm, and the roughness is controlled to be 0.5~0.8um.

The inner thread sealing section 13 starts from the shoulder surface, and constructs a radial cone sealing surface 131 composed of a small radius arc sealing surface 132 (0.8-1.5mm) and a conical sealing surface 131 (taper angle 10-25°). , the axial length of the sealing surface of the inner thread sealing section 13 is not less than 3.3mm, which optimizes the total sliding distance after the sealing surface contacts, which not only ensures the integrity of the sealing surface but also realizes the high-pressure sealing ability under high tension. The tapered sealing surface 131 can be completed by rough turning and fine turning. The change of the measurement value caused by the axial change of the sealing diameter measurement control point is a simple linear relationship, which is beneficial to the measurement control accuracy, and overall achieves easy processing and quality control. .

As shown in Figure 2, the sealing surface of the female threaded joint 1 is a tapered surface, the taper angle is 15°, and the 1mm radius arc is connected to the shoulder surface. The length is 3.4mm; the sealing surface of the male threaded joint 2 is a circular arc surface, the main sealing surface is formed by a 45mm radius circular arc surface, and the 2mm radius circular arc surface is used as the guide surface to connect to the shoulder surface, which naturally disappears in the threaded part, sealing The axial length of the face is 3.6 mm.

More preferably, the position of the last stage tooth of the inner thread of the casing close to the sealing surface is provided with an undercut which takes into account the functions of retraction and thread grease storage, so as to achieve no interference with the nose end of the external thread after making up. The axial length of the inner thread relief groove is specifically set to be 1 to 1.5 times the pitch (ie, 5.08 to 7.62 mm).

As shown in Figures 2 and 3, the shoulder surfaces of the internal thread shoulder section 14 and the external thread shoulder section 23 can be selected as right angle (0°) or negative angle shoulder surface (-3°). The inner surfaces of the hoop connections are flush. When the right-angle shoulder surface 14-1 of the female thread shoulder section is used as shown in Figure 2, the right-angle shoulder surface 23-1 of the male thread shoulder section is also corresponding to the right-angle shoulder surface 14-1 of the female thread shoulder section. 1 Matching; when the negative angle shoulder surface 14-2 of the female thread shoulder section is shown in Figure 3, the negative angle shoulder surface 23-2 of the male thread shoulder section is also corresponding to the negative angle of the female thread shoulder section. Shoulder face 14-2 match.

As shown in Figure 4, the thread profile of the outer thread and the inner thread of the casing adopts the profile that is interchangeable with the API standard buttress profile. The thread bearing surface angle of the API standard trapezoid profile is 3°, and the thread guide surface is The angle is 10°.

The taper of the external thread segment 21 is 1.59mm in diameter increment per 25.4mm axial length (the range of diameter increment per 25.4mm axial length is: complete thread segment -0.038～+0.089mm and incomplete thread segment -0.038 ~+0.114mm), the tooth top and tooth bottom of the external thread segment 21 are parallel to the busbar.

The internal thread can choose to use the same taper of the external thread, or the variable taper scheme can be selected. The internal thread variable taper adopts the center diameter point at the axial distance of 40mm from the shoulder as the axial boundary. According to the pitch of 5 threads per inch, the arc transition is set with an axial range of one pitch (5.08mm), and the radius of the arc is 95~110mm can be used, and the larger taper is actually set on the side close to the end face of the coupling, that is, a taper tolerance zone with a diameter increment of -0.015~+0.114mm per 25.4mm axial length is used; The side of the shoulder surface is actually set with a small taper, that is, the incremental change range of the diameter per 25.4mm of axial length is -0.064 to +0.025mm.

The internal thread section 11 can selectively adopt the thread taper scheme. On the premise of ensuring the anti-torsion performance of the thread, the circumferential deformation of the coupling can be controlled, the radial contact pressure of the main seal can be selectively increased, and the impact on the negative angle of the shoulder can be further reduced. Rely on, optimize the thread sealing and torsion resistance, and realize the flexible design of the threaded joint structure; the thread taper can achieve smooth connection through the arc transition section, avoiding local stress concentration. The thread taper scheme is realized by the control change of the thread taper tolerance zone. The optimized taper tolerance parameters ensure the performance and machinability of the flexible design; the large tolerance zone setting of the taper thread is adopted, and the parallel generatrix of the taper surface of the thread is easier to process and control. The structure reduces the processing cost on the premise of ensuring the performance of the threaded connection.

The complete thread axial length of the optimized external thread can be increased by 20 to 30 mm, and the pitch diameter of the internal thread can be increased by 0.1 to 0.2 mm. The complete axial length of the external thread and the pitch diameter of the internal thread are optimized to ensure the smoothness of make-up and the connection performance after make-up. The above design realizes the requirements of processing versatility, operation interchangeability and manufacturing economy under the premise of satisfying the working conditions parameters.

Many of the above design elements reflect the applicability of manufacturing economy and working conditions. For example, adopting the tooth form interchangeable with the standard tooth form can save more than 50% of the thread processing cost, at the same time increase the thread bearing area by increasing the axial length of the complete thread, and optimize the thread interference by changing the pitch diameter of the thread, thereby improving the make-up. High anti-velcro performance, the axial connection efficiency after buckle can achieve 100% pipe body strength, and the requirements of processing versatility, operation interchangeability and manufacturing economy can be achieved under the premise of meeting the working conditions parameters.

The arc surface-cone surface metal interference sealing structure is adopted, and the sealing surface structure adopts a small-radius arc as the guide surface of the make-up on the external thread, which disperses the contact pressure when the sealing surface starts to contact during the make-up process, and greatly reduces the risk of the sealing surface sticking; The external thread adopts a large-radius arc as the main sealing surface of the radial arc surface, which increases the sealing contact width, and the contact pressure is distributed normally after the buckle is engaged, which improves the robustness of the sealing structure; at the same time, the main sealing contact point and the shoulder are maintained. distance, reducing the risk of mechanical bumps during the buttoning process. The sealing surface of the external thread is completed by a simple nose end chamfering process to ensure that the axial length of the sealing surface is not less than 3.5mm, and the sealing surface of the external thread naturally disappears in the threaded part. On the one hand, the processing cost of the thread sealing surface is greatly reduced, and on the other hand, the anti-compression performance of the thread nose is greatly improved. The internal thread sealing surface starts from the shoulder surface, and constructs a radial cone sealing surface 131 composed of a small radius arc and a small angle cone surface, which not only optimizes the total sliding distance of the sealing surface after contact, thereby improving the resistance of the sealing surface. Velcro and high-pressure sealing ability under high tensile state, and the main sealing cone surface is easy to process and control.

The thread design adopts the shoulder structure of -3° and 0° angle, which brings about a significant improvement in the torsion resistance and compression resistance of the thread. Processing cost, convenient for maintenance operations such as on-site cleaning. Considering the contradictory relationship between the increase of the shoulder angle and the improvement of the sealing performance and the reduction of the compressibility, the combination of two shoulder angles is adopted to meet the requirements of different working conditions. At the same time, the internal thread of the butt-coupling adopts two schemes of fixed taper and variable taper. The variable taper scheme is to slow down the taper of the internal thread near the pipe end of the external thread, reduce the risk of sticking, and improve the contact pressure of the sealing surface; The disappearing end adopts increased taper of the internal thread to ensure the thread is screwed in place and the anti-torque ability. By selectively adopting the internal thread variable taper combination, a reasonable matching of torsion resistance and sealing performance is achieved. Furthermore, the variation of the shoulder angle and the taper of the thread further strengthens the individual characteristics of the thread as a whole, forming an economical sealing structure suitable for different levels of internal pressure and compression performance, and realizing the flexibility of the design and manufacture of the threaded joint.

The special threaded joint can be adapted to select casings with different outer diameters, wall thicknesses and steel grades. When making up, apply universal casing thread grease evenly on both ends, the clamping thread is close to the pipe body side and the coupling is close to the factory end side, and the best control torque is used on site to make up.

After the assembly is completed, the inner wall of the outer threaded end of the casing is provided with an expanded conical surface, which is flush with the junction of the inner threaded end of the casing, so as to improve the fluid erosion resistance of the inner surface of the joint.

After the assembly is completed, the radial sealing structure of the circular arc surface and the cone surface is formed between the outer thread and the inner thread of the casing. Since this sealing structure does not require the transition between the cylindrical surface and the threaded part, a simple radial sealing is realized, and the The variable combination of shoulder angle and thread taper forms an economical sealing structure suitable for different internal pressure levels.

According to the different needs of working parameters, especially the different requirements for the comprehensive performance of threaded joints against gas internal pressure and torsion resistance, through the combination of variable taper and different shoulder angles of the internal thread, combined with a simple sealing structure, different characteristic performances can be achieved. Subdivision, that is, starting from the needs of different anti-internal pressure and anti-torsion working conditions, select different internal thread taper and shoulder angle matching schemes, reflecting the product's flexible design, manufacturing process and working conditions applicability, as shown in the following table.

The above design ensures the smoothness of the buckle and the tensile and compressive properties of the buckle. The invention is suitable for shale gas and shale oil wells in the long-distance horizontal and large dog-legged wellbore casing running process of lifting and lowering pressure, rotation and bending process, and improves the fracturing load cycle conditions of shale gas wells and shale oil wells. The water sealing performance meets the gas sealing performance requirements of the shale gas well in the production stage. In particular, the general design of the transition between the external thread sealing surface and the threaded part is changed from a cylindrical surface, and the external thread sealing surface starts directly at the end of the pipe body and disappears into the threaded part.

The present invention adopts the above technical scheme, the threaded joint is easy to process, easy to make up, the axial tension/compression, internal pressure/external pressure performance can reach the same strength as the pipe body, and it is suitable for deep shale oil and gas reservoirs in my country and fracturing. High pressure, large displacement, long production target cycle and other working conditions.

The above content is a further detailed description of the present invention, and it cannot be considered that the specific embodiments of the present invention are limited to this. Several simple deductions or substitutions should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims (10)

1. A casing special threaded joint for multistage fracturing of unconventional oil and gas horizontal wells, is characterized in that, comprises the male threaded joint (2) and the female threaded joint (1) that can adopt the coupling type connection; The external thread joint (2) comprises an external thread segment (21), an external thread sealing segment (22) and an external thread shoulder segment (23) which are connected in sequence; the external thread sealing segment (22) comprises an external thread main sealing surface (221) and the external thread sealing surface guide surface (222); the external thread main sealing surface (221) and the external thread sealing surface guide surface (222) are both arc surfaces; The female threaded joint (1) comprises an internal threaded section (11), an undercut section (12), an internal threaded sealing section (13) and an internal threaded shoulder section (14) which are connected in sequence; the internal threaded sealing section (13) includes The conical sealing surface (131) and the circular arc sealing surface (132), the conical sealing surface (131) is connected with the undercut section (12) through the circular arc transition surface, and the circular arc sealing surface (132) is connected with the inner thread shoulder segment(14) connection; When the male threaded joint (2) and the female threaded joint (1) are engaged, the male threaded sealing section (22) is in contact with the female threaded sealing section (13); The thread profiles of the external thread segment (21) and the internal thread segment (11) are both interchangeable with the API standard buttress profile. 2. The special threaded joint of casing for multistage fracturing of unconventional oil and gas horizontal wells according to claim 1, characterized in that the inner thread shoulder section (14) and the outer thread shoulder section (23) are The shoulder surfaces are all right-angled shoulder surfaces or negative-angled shoulder surfaces. 3. a kind of unconventional oil and gas horizontal well multi-stage fracturing casing special threaded joint according to claim 2, is characterized in that, the shoulder angle of the right-angled shoulder surface is 90° with the casing axial direction, and the negative angle is 90°. The shoulder angle of the shoulder surface is -3° to the radial direction of the tube. 4. A special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells according to claim 1, characterized in that the taper angle of the conical sealing surface (131) is 10-25°, and the inner thread seals The axial length of the sealing surface of the section (13) is greater than or equal to 3.3mm, and the roughness is controlled to be 0.5-0.8um; The radius of the arc sealing surface (132) is 0.8-1.5 mm. 5. The special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells according to claim 1, wherein the arc radius of the main sealing surface (221) of the external thread is 30-80 mm, and the external thread The arc radius of the sealing surface guide surface (222) is 1 to 2 mm; The axial length of the external thread sealing section (22) is greater than or equal to 3.5mm, and the roughness is 0.5-0.8um. 6. The special threaded joint for casing for multistage fracturing of unconventional oil and gas horizontal wells according to claim 1, wherein the undercut is used for retracting and storing thread grease, and the axial length of the undercut is It is 1 to 1.5 times the pitch. 7. The special threaded joint of casing for multi-stage fracturing of unconventional oil and gas horizontal wells according to claim 1, wherein the taper of the external thread section (21) is a diameter increment per 25.4mm axial length 1.59mm, the tooth top and tooth bottom of the male thread segment (21) are parallel to the busbar. 8. The special threaded joint for casing for multistage fracturing of unconventional oil and gas horizontal wells according to claim 1, wherein the inner thread section (11) adopts the same taper as the outer thread section (21); Or the internal thread section (11) adopts a variable taper scheme, specifically: Taking the mid-diameter point as the axial boundary, set up a circular arc transition section within the pitch range, with different taper tolerance zones, the side close to the end face of the coupling is a large taper section, and the side close to the shoulder surface is a small taper The tooth top and tooth bottom of the female thread segment (11) are parallel to the generatrix. 9. a kind of unconventional oil and gas horizontal well multi-stage fracturing casing special threaded joint according to claim 8, is characterized in that, the larger taper section adopts the diameter increment variation range on every 25.4mm axial length to be- Taper tolerance zone of 0.015～+0.114mm; The small taper section is set with a taper tolerance zone with a diameter incremental change range of -0.064 to +0.025mm per 25.4mm axial length. 10. A special threaded joint for casing for multi-stage fracturing of unconventional oil and gas horizontal wells according to claim 1, characterized in that the axial length increase of the complete thread of the external thread section (21) ranges from 20 to 30 mm; The increase range of the pitch diameter of the internal thread segment (11) is 0.1-0.2 mm.

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