Development of Gastight, Pressure-Rated, Third Generation Rotary Shouldered Connections for 20,000-psi Internal and 10,000-psi External Pressure Service

Abstract

This paper presents the results of a two-year comprehensive effort to design, test, and qualify third-generation rotary-shouldered connections (RSC) for 20,000 psi internal and 10,000 psi external pressure service. ISO13679 testing methodologies for casing and tubing were modified to evaluate the RSC pressure capability. Results from comprehensive finite element modeling and extensive laboratory testing designed to reproduce the harsh, aggressive loading modes and high pressures encountered in field use are presented. The result of this program is a RSC that incorporates a double-start thread form to reduce the number of revolutions to assemble the connection by 50 percent reducing trip time. The thread form also provides a unique dual-radius thread root that offers a step change improvement in fatigue resistance. A metal-to-metal seal provides pressure integrity. In addition to providing a 20,000 psi internal and 10,000 psi external pressure rating, the new connections provide increased mechanical and hydraulic performance compared to second generation high torque connections while also providing fatigue performance greater than standard API connections. Introduction New developments in drilling tubulars are rapidly evolving and represent enabling technologies for the industry's continued advancement of drilling deeper, further and more cost-effective wells. Much focus has been made toward the advancement of RSC technology to permit high torque drilling of extended reach, directional and horizontal wells. In response to this need, the development of third generation, ultra-high torque connections was recently announced providing reduced tripping times and the mechanical and hydraulic load requirements for drilling today's deepwater, extended reach and ultra-deep wells. The next step in the evolution of RSCs has now occurred with the development of a third-generation, gas-tight, pressure rated connection providing enabling technology for high-pressure completion and workover, drill-stem testing, UBD and intervention riser applications. Although drill pipe, drill pipe connections and drill stem materials represent mature technologies, innovations are being developed in these areas. This third generation gas-tight, double-shoulder connection presented here represents several advancements that address some of the challenges ahead. Double-Shoulder Connection Design Development First generation double-shoulder connections (1st Gen. DSC), see Figure 1, were introduced in the early 1980's.4 1st Gen. DSC's were basically API rotary-shoulder connections (primarily NC or FH) with a second torque shoulder added inside the box member at the pin nose interface.1,3 These 1st Gen. DSC's incorporated the same basic design features in terms of thread form, taper, lead, pitch diameters, etc. as the API connection on which they were based. These connections yielded a simple, straight forward solution that increased the connection torsional strength by approximately 40 percent over the corresponding API connection.

Force analysis and tightening optimization of gas sealing drill pipe joints

“…Taking the XT-M tool joint that is developed by GRANT Company as an example, the torsional strength of XT-M is about 70% higher than API joints and the gas sealing performance is satisfactory, which is confirmed by an experiment that XT-M joints can seal 20,000 psi internal pressure and 10,000 psi external pressure load [1].…”

Finite Element Numerical Simulation of Tubing Premium Connection

“…The threaded connection was modeled using an elastic-plastic relationship and axisymmetric quadrilateral element with non-liner deformation. [3,4] The element has two degrees of freedom per node. The analysis examples presented in this paper will consider an 88.9mm, Grade 110 premium connection of tubing connection.…”

Design Optimization for the Thin-Walled Joint Thread of a Coring Tool Used for Deep Boreholes

“…Although API RP 7G provides the ultimate working torque for API RSCs, the relationship between the ultimate working torque and axial tension is simplified to be linear, which is only true when the axial tension is not too large [25]. The stress distribution in API joints is not reasonable, which results in a short service life [26]. For a drilling pipe, taking the XT-M tool joint developed by GRANT Company as an example, the torsional strength of XT-M was higher than that of API joints, and the gas sealing performance was satisfactory, which was confirmed through an experiment in which XT-M joints sealed an external pressure load [27].…”