Offshore Drilling and Production Time-Saving Quick Connect and Disconnect Wellhead Connectors
Authors: Adamek F.C. , Humphrey B. 
Published: October 2008

In this development effort, a new family of wellhead connectors was designed, analyzed, and tested. The design criteria are outlined, the optimization routine is described, and the weight capacity and the makeup time are described in comparative terms relative to the API flange. The test results for a connector design are compared with finite element analysis (FEA), and the results are correlated with the predictions and criteria.

INTRODUCTION

The traditional API flange and clamp connections have served the industry well for many years. Some of the disadvantages of these connection systems include slow makeup times, high torques, and handling problems. These drawbacks, along with a requirement for increased safety and efficiency, indicated a need for an alternative end connection. An initial incentive was provided by an oil company that required a wellhead system for a slant drilled well where flange makeup would be difficult. The "other end connection" (OEC) used for this application was based on a marine riser connection which has been used in subsea drilling for many years and fulfilled the end user's requirement that the OEC utilize "field-proven technology." (Figure 1).

The long term industry requirement was reviewed, and a functional and operational requirement specification was generated. The main features of this specification were as follows:

Safety:

The mandrel should have an outside diameter that is capable of passing through either a BOP stack or diverter (depending on connection size). This would facilitate the landing of casing hangers and setting of the packoffs with BOP protection.

Connection Capacity:

The connection should have a capability equivalent to the API flange, considering pressure, tension, and bending. Connection separation would be deemed as connection failure.

Connection Makeup:

The connection should be fast makeup (initial target of 15 to 30 minutes for a 13-5/8", 15,000 psi connection). The required makeup torque should be minimized (initial target of 1,000 ft-lb for the 13-5/8", 15,000 psi connection. Ideally, no specialized tooling should be required for makeup or breakout of the connection.

Performance Verification:

The connection should meet the performance verification testing to PR2 as outlined in API 6A, Sixteenth Edition, Appendix F. The temperature rating of the connector should be in line with API 6A classifications P through X.

DESIGN AND DEVELOPMENT

Common Mandrel For New Designs:

Having established the desirability of an OEC, a brief review of the market was made and outline concepts were produced. It was felt that a low cost clamp type connection should be developed for production applications where a single or low number of makeup cycles was likely (the NF clamp, Figure 3). The dog type connector would be required for the drilling (BOP) mode (the NT-2 connector, Figure 4A).

It was felt that the number of mandrel profiles should be minimized and that the mandrel profile should be common for all pressure ranges within a certain nominal size. This would ease any interface problems with BOP stacks. A decision was made to design and prototype test the following sizes: 13-5/8", 15,000 psi and 21-1/4", 5,000 psi.