The Design of Tubing and Casing Premium Connections for HTHP Wells

Abstract

Abstract The design of premium connections for casing and tubing applications in HT/HP wells, especially in sour environment, require the consideration of extreme design conditions not present in common applications. The high pressures to stand and seal -both internal and external, and the limitations on steel yield strength due to sour environment provokes an increase of wall thicknesses, adding challenges to obtain simultaneously enough structural resistance, good seal response and low resistance to galling. The design of specific and very tight stress relief procedures is a key element to keep the material resistance to sour environment, when swaging or expansion required. Regarding design performance verification, it is based on the use of a combination of very refined non-linear Elastic-Plastic Finite Element Analysis, together with the testing concepts of new standard ISO 13679 / API 5C5, which expose the connection to a very demanding evaluation in terms of resistance to galling, extreme combined loading conditions -tension, compression, internal pressure, external pressure, bending, thermal cycling, and limit load. This paper describes, through actual examples, the design process and the key elements that need to be considered in the design of a high performance premium connection for HP/HT Sour wells, from the paper to the manufacturing process, including the ways to balance the design features for optimum performance, and the different tools and evaluation methods required to validate the designs. Introduction The high pressures and temperatures in HPHT wells require the maximum performance of premium connections. The addition of sour environment introduces an additional requirement with clear impact on the connection design (when thicker wall thicknesses required) while pushing the manufacturing technology limits.