Ultrasonic Techniques Accurately Examine Seal-Surface Contact Stress in Premium Connections
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110675, "Using Ultrasonic Techniques To Accurately Examine Seal-Surface Contact Stress in Premium Connections," by Kirk Hamilton, SPE, Brian Wagg, SPE, and Tim Roth, CFER Technologies, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed.
One of the most important functions of a tubular connection is sealability. This is especially the case for premium connections commonly used in the demanding conditions of high-pressure/high-temperature (HP/HT) and thermal-well applications. Sealability also is one of the most important criteria used during connection qualification. Ultrasonic inspection technology provides a means to obtain nonintrusive measurements of contact stress between two mating metal surfaces separated by a thin lubricating film.

Introduction
Resources thought unrecoverable only a few years ago now are being targeted by operators, however, the extreme environments where many of these resources are located pose unprecedented operational and technical challenges. As a result, wellbore-integrity-management (WIM) systems have become important components in well design for many operators. Critical well designs include premium connections, which generally offer better sealability compared with standard American Petroleum Inst. (API) connections. However, the sealing systems in premium connections can be damaged either during makeup or as a result of exposure to the service environment. Current connection-makeup acceptance criteria are based primarily on makeup torques (shoulder and final), which may not be associated directly with connection seal integrity and overall sealability.

Wellbore Integrity
Wellbore integrity is an important component of current well-design practices. WIM and WIM programs focus on prevention of uncontrolled fluids releases across well barriers including tubing, casing, packer elements, and cement sheaths over the full construction, service, and operational life of the well for worker safety, environmental protection, and well-production efficiency. Connections in casing and tubing strings play a critical role in preventing fluid loss and maintaining wellbore integrity.
Two areas of concern for connections are leakage to the environment and sustained casing pressure. In both cases, an accumulation of fluid in the ground around the well, in the annular space between casing strings, or between casing and tubing strings can lead to contamination, corrosion, and even in some cases, loss of the well and catastrophic blowout situations. Operators have recognized these issues, and considerable efforts have been made to mitigate them through proper well design and construction techniques, equipment selection and installation techniques, and safe operating procedures.
Proper tubing- and casing-connection selection is a very important step that operators need to take to ensure that risk of leakage past connections is minimized. It is estimated that approximately 90% of all tubing and casing leakage failures are attributed to connections. This percentage is high, but it takes into account the large number of casing and tubing connections relative to other potential downhole leak paths (e.g., packer elements and pipe-body failures).