Drilling and completing wells deeper, and in HPHT sour environments, magnifies the importance of having reliable threaded casing and tubing connections. High pressure/high temperature wells present many critical challenges for threaded tubular connections. Through design, proof testing, and installation, premium connections are meeting these requirements in a number of ways. With coupling stock for thick walled tubulars and sour service environments often being the limiting factor as the pipe wall increases, integral connections, and threaded and coupled designs with pin to pin contact allow the use of production casing over one inch in wall thickness. The incorporation of resilient seals into threaded and coupled connections can offer secondary back-up seals to the primary metal to metal seals.
Premium connection designs are often required to be validated or pass a qualification test program before acceptance by the users. Two fundamental approaches exist for qualification testing; product line testing and project specific testing. Product line testing is used to "qualify" a range of dimensions and wall thickness within a given design and is often accompanied by Finite Element Analysis (FEA). Project specific testing is used for very critical applications and when the connection designs are tailored to meet specific requirements. The ISO 136791 test procedure is most commonly used as the basis for qualification testing although "modified" ISO and other qualification test procedures are also used.
The design and qualification of HPHT connections determine that the connections are fit for purpose and that they provide reliability for HPHT well applications. The installation process is also a critical issue in the successful drilling and completion of such wells. Computer controlled make-ups, low stress or non-marking dies in handling equipment and even the application of the proper thread compound and quantity can be critical components in the successful completion of HPHT sour wells.