The Evolution of Expandable Technology
Authors: Bailey Greg 
Published: February 2015

Management
Emerging industry standards and continued technology advances are supporting broad industry acceptance of expandable tubulars as a common element in enhancing the economics and performance of both new and old wells. The growing reliability and utility of the technology have quickly evolved an extensive range of standard applications across drilling, completion, and production operations.
Soon after its introduction, expandable technology was incorporated as more of a contingency of last resort in deepwater drilling programs. However, a far greater scope of well-site use in much more common applications would require advancement in hardware and experience in running the systems. Today, expandable tubulars are enabling new wells to be drilled in difficult reservoirs and have become a powerful tool in extending the lives of mature assets.

Technology Advancement
While reliability has steadily increased to an average of more than 95%, expandable pipe presents some unique operational challenges related to differential sticking, hole restrictions, and high build rates. Common to all drilling operations, these problems have slightly different ramifications for expandables. Refinements in technology and operating procedures are effectively addressing these issues.
For instance, because the expandable system is run into place while supported at the bottom of the liner string, one could expect that tension be reduced. However, if hole friction or differential sticking restricts the pipe and prevents it from shortening during expansion (a fixed-fixed situation) an additional 100 to 200 kips of tension can be imparted to the string. Combined with other forces, this could exceed connector or pipe tensile limits. Awareness and close observation of restrictions during string installations is a key to avoiding this type of problem.
For this reason, hole conditions continue to dramatically affect the success rate of expandable installations. Tortuosity and hole curvature can result in torsional forces being inflicted upon the connections. Installation in a smooth, nontortuous wellbore ensures pipe is run and expanded efficiently.
Technology refinements and innovation have improved the reliability and broadened the application of expandables. These advances include strengthening the connections, increasing makeup torques, and reducing friction.
Connector development is an ongoing process. Expandable connections have unique stress demands because they must often remain a pressure barrier after expansion. Early improvements added a connection sleeve to protect the connector from damage to the outer surfaces during installation. Scores and notches inflicted during running create stress, so protecting the connectors from this damage prevents associated failure modes during expansion.
Next, the torque shoulder region of the sleeve was modified to increase torsional capacity. More recent innovations include new designs that aid reliability through increased pipe-wall thicknesses and improved seal geometry. To improve the expansion process, friction-reducing coatings have been added on the inner diameter of expandable pipe.