Low SCF Integral Premium Connections for Use in Highly Demanding Casing and Tubing Drilling Operations
Authors: Carcagno Gabriel E. , Bufalini Andrea , Conde Luis , Toscano Rita 
Published: October 2008

Abstract
The diffusion of new techniques such as casing drilling, tubing drilling or tubingless completion are requiring the development of connections with performance features not common in standard tubing and casing connections. High resistance to fatigue loading, high overtorque capacity, and sealability after drilling are key performance features difficult to find in available tubing and casing connections.
This paper describes the development, evaluation and uses of an integral type premium connection for tubing/casing also suitable for drilling applications under very demanding conditions. Finite Element Analysis performed in combination with full-scale fatigue, overtorque and sealability tests were used to assess the application of the proposed connection design. FEA analysis confirmed a very low Stress Concentration Factor (&lt; 2.0), while full-scale tests for fatigue showed no fatigue crack development through 2 million cycles with dog leg severity as high as 30° / 100' for a 4 ½" 12.7# P110 tubing string.
The connection evaluated has been successfully used in Mexico in tubing drilling applications and left in the well as the production string (tubingless technique). This connection was also used for several deep wells with highly demanding repair activities and subjected to more than 200 hours of effective rotation and 30 round trips.
This type of connection design minimizes the limitations of these new techniques which can ultimately be expanded to more challenging deeper or highly deviated wells.

Introduction
The Casing Drilling is one of the new fast growing drilling techniques, because it has proven to be a good method to reduce drilling costs and to solve some typical drilling problems [1,2]. As the technique is developed, the problems associated with any new technology are being solved and the application limits are expanded toward more demanding conditions. Hence, although today the applications are concentrated in shallow vertical wells, the use of casing drilling techniques for directional wells is being considered [3]. However, the use of standard casing connections on these wells is affected by the limitations of connection performance due to the peculiar loading conditions, mainly concerning the fatigue resistance due to the oscillating stresses from string rotation and curvature, and the higher torque capacity required to overcome torque and drag [4].
Another application that requires very robust connection is related to the well repairing jobs where several round trips are expected. In order to optimize cost and time, the use of a production tubing string to perform this job instead of using the drill pipe can be implemented if a rugged, high torque resistant, high fatigue resistance tubing connection is used. In that way, once the workover job is finished, the string can then be used for production.
In this paper, a premium type integral connection particularly capable for the above mentioned applications is described. Technical features, Finite Element Analysis support, laboratory experimental evaluation and actual field experiences are described. It was verified that the ability of this type of connection for applications such as drilling with casing can satisfy requirements such as:high fatigue resistancehigh overtorque resistanceexcellent make & break behavior (&gt; 20) andmaintenance of sealing properties.