This disclosure relates to a tubular coupling assembly, for example, a coupling member coupled to two pins such as two tubulars, to form sealed assemblies.
Wellbore tubulars can be axially coupled, end-to-end, using threaded joints. One technique to couple two tubulars is using buttress threads and a hollow coupling. A first end of a first tubular has a thread profile on a tapering outer surface. A first end of the second tubular also has a thread profile on a tapering outer surface. The coupling is a hollow member that has complimentary internal threads on its inner surface. The inner surface of the coupling also tapers from respective ends of the coupling towards a center of the coupling. The threads are formed on the tapered portions. An unthreaded shoulder joins the two tapered portions of the coupling. The threaded end of the first tubular and the threaded end of the second tubular are screwed into respective ends of the coupling. The thread profile is a buttress thread that joins the two tubulars and also seals the outer surfaces of the two tubulars to the inner surface of the coupling.
This specification describes technologies relating to a tubular coupling assembly with modified buttress thread.
The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.
Like reference numbers and designations in the various drawings indicate like elements.
This disclosure describes a coupling assembly (i.e., a combination of a coupling member and two tubulars) that solves a challenge of leakage into annuli in wellbores, for example, due to poor zonal isolation post a cementing stage. Such poor zonal isolation can lead to ingress of hydrocarbon between intermediate and/or outer casing strings. The coupling assembly described here provides improvement in long term well integrity by improving the barrier element. The coupling assembly can be used as a gas tight connection for large diameter tubulars in shallow gas intervals or as production string for gas wells, oil wells with high GOR oil and gas-lift applications. The coupling assembly can form a hybrid or metal-to-metal (or both) connection with buttress thread form and pitch and can be used in API or proprietary connections.
In some implementations, each of the first tapered axial portion 120 and the second tapered axial portion 124 can include a respective pocket (e.g., pocket 114) that can accommodate excessive dope (i.e., a sealant used with threaded pipes to create a seal) when the coupling member 100 is coupled to the two pin connections, i.e., the two tubulars. In some implementations, the pocket 114 can accommodate excessive dope applied during make-up process and reduce the risk of humping and leaking connection. The pocket 114 can be included in the pin connection around the initial partial or unengaged threads such that at final make-up (i.e., contact with the concave shoulder), there is a pocket or a space in the connection to accommodate the excess dope during make-up process. The pocket 114 formed by the pin is not limited to using the overlap between the plane of end of power tight to the plane of hand tight of a standard buttress with no threads on the pin to create a gap. Alternatively, the pocket 114 can be included in the coupling member 100 or both connections (tubulars and the coupling member 100) in the initial partial or unengaged threads zone. The dimension of the pocket 114, whether in the pin or the coupling member or both, should have minimum impact on the compression capacity of the connection at final make up.
In some implementations, the dimension of the shoulder 200 is such that the middle section of the concave shape, which will have the most stress in the shoulder 200, has sufficient thickness to withstand compression loads without plastic deformation of the shoulder 200. Ends of the shoulder 200 are comparatively thinner and trimmed compared to the middle of the shoulder 200. Such design prevents easy chipping during connection make-up or well intervention. Due to the design described here, additional incremental turn after shoulder contact of the pin connection imposes sufficient compressive load on the metal-to-metal seal 108 to ensure a gas-tight seal integrity without plastic deformation of the pin nose. Inclusion of the load shoulder 200 delivers a flush inner diameter in the buttress connection. Also, the base triangle correlates with the shoulder contact of the pin with the box connection and make-up torque ranges can be provided for different connections depending on the grade and weight. This is in contrast to the current reliance on average torque to reach the base triangle during make-up process.
The use of the metal-to-metal sealing system in the buttress connection eliminates limitations with interference or common resilient seals used in some modified buttress connections. Examples of failures that the disclosed coupling member eliminates includes (i) temperature degradation of interference or resilient seal; (ii) dynamic failure of interference or resilient seal under cyclic pressure especially when used as a production string; (iii) seal failure under compression load; (iv) chemical degradation of resilient seal or interference seal.
The coupling member 100 can include a seal ring groove 301 (shown in
The combination of metal within the seal 300 improves the stability, strength and temperature limit of the seal. In some implementations, the seal 300 can encapsulate a metallic strip 304. Together with the metallic strip 304, the seal 300 forms an inverted trapezoidal shape. The materials (e.g., the polymeric or elastomeric materials, the metal for the metallic strip, and other materials used to make parts of the seal 300) can be selected such that there is a compatibility between the seal material and the metallic material that reduces risk of shear failure of the seal 300 during make-up process. Depending on the type of material and the seal contact areas, the shape of the seal need not be an inverted trapezoid.
The coupling member 100 described in this disclosure can be used in a top-hole application for tubulars having diameters greater than 16 inches or deeper hole applications for tubulars having diameters less than 13⅜ inches (or both). The former can utilize a hybrid seal (e.g., the seal 300) as a secondary sealing mechanism. The latter can be used using the metal-to-metal seal. The modified buttress connection with a metal-to-metal seal can also be used as a gas-tight connection in shallow gas intervals or where there exists a risk of gas migration between intermediate casing and the wellbore surface.
In sum, implementations of the subject matter can reduce erosion risk of the connection post make-up process and deployment. The approach involves reducing turbulence in the coupling section between two ends of the tubulars post connection make-up. Elimination of the unengaged thread section in the coupling and ensuring a flushed ID with the shoulder reduces the risk of turbulence in the area while drilling the next hole section or during production if used as a production string. The approach also limits the degree of abrasion in the coupling in this section to wear and ultimately connection leak. Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims.