Beyond Stress Relief Features...The Bottom Hole Assembly Connection for the Harshest Fatigue Environments
Authors: Chandler Raymond Brett , Muradov Andrei , Payne Michael Lyle , Wright Jon C. , Jellison Michael J. , Reeves Michael Edward , Pixton David 
Published: December 2007

This paper describes the development, design, lab and field testing of a new generation rotary shouldered connection for BHA components.Originally pursued to enable data transmission through the BHA, this new connection further provides a dramatic increase in fatigue resistance to cyclic loads.Additional benefits from the optimized design are gained in handling and repair performance.Lab results from resonant bending fatigue tests are discussed.Successful results from the industry's first field trials of these new connections are also provided.The paper describes a critical field application where the new BHA connection has been selected to provide advanced fatigue resistance.The paper further illustrates how the connection may be used in the harshest fatigue environments to minimize risk of failure and improve well economics.

Introduction

New developments in drilling tubulars are rapidly evolving and represent enabling technologies for the industry's continued advancement of drilling deeper, longer reach and more cost-effective wells.Much focus has been made toward the advancement of drill pipe connection technology to permit high torque drilling of extended reach, directional and horizontal wells.During development of these high torque connections, manufacturers have also advanced the connection fatigue performance through the use of proprietary thread forms.

Yet there has been no significant development in bottom hole assembly (BHA) connection technology since the introduction of stress relief features (SRF) and cold rolling practices to the thread roots.The predominant use of American Petroleum Institute (API) NC and Regular connections within the BHA serves to maximize the compatibility of the industry's inventory of BHA tools, but does not necessarily optimally address the cyclic loading conditions that exist within every BHA.Fatigue continues to be the most common failure mode in the BHA and represents one of the most costly drilling problems, often requiring lengthy trips, open hole fishing and sidetrack operations.

In order to address this industry need, a comprehensive two-year program to design, develop and test a highly fatigue resistant BHA connection was pursued.As a result of the program, a new proprietary connection was developed with test results that indicate at least nine times improved fatigue performance when compared to standard API connections.

Developed for the IntelliServ® network, the new connection incorporates a secondary internal shoulder, which can house inductive coils to permit telemetry transmission across the drill collar connection.

Project Background

The IntelliServ network, a high-speed, bi-directional, real-time drill string telemetry system, has been under development since 1997.This network utilizes conventional drilling tubulars modified to incorporate a 3/16 in. diameter high-speed data cable running the length of each joint.The cable terminates at unique, inductive coils that are installed in the pin nose and corresponding box shoulder of every connection.

A double-shouldered connection provides an ideal location for coil placement, with each coil installed in a protective groove in the secondary torque shoulder.Figure 1 illustrates a coil installed in the pin end of a double-shouldered drill pipe connection.