Field Testing of High-Strength Rotary Shouldered Connections in Difficult Drilling Conditions

Abstract

Rotary shouldered connections on a bottom hole assembly (BHA) are most susceptible to twist-offs during high-fatigue drilling, which lead to expensive fishing jobs and loss of productive time. The increasing use of rotary steerable systems and the difficult drilling conditions in land operations demand threaded connections that are substantially stronger than the existing API ones. This paper is meant to present the field test results of two newly developed connection designs in harsh drilling environments. The high-strength connections were developed by devising and optimizing a new thread form and applying an advanced manufacturing process. Experimental results from full-scale fatigue tests indicated ten-fold fatigue life extensions over their existing counterparts at a given dogleg severity (DLS) level. The aspects that could not be covered in laboratory conditions were evaluated in field environments. These include on-rig makeup and breakout, downhole drilling conditions, field inspections, and recuts. The field testing program underwent using one new connection on a BHA, replacing all existing connections with the new ones, and eventually having a fleet of BHA components with the new connections. All field trials on the two new connections, one being a shop joint and the other a field joint, were conducted in client wells with over 100 runs on North American land. More than 717,000 drilling feet and 9,500 drilling hours have been accumulated. The connections were used per the existing common field practices to drill both curved and lateral sections. The maximum DLS achieved was 17°/100 ft. The longest lateral section drilled in one run was more than 19,500 ft. The large curvature in the curved section, along with the long lateral section where noticeable local DLS was frequently encountered in interbedded formation, posed a substantial risk of fatigue failures to the connections. Nevertheless, no twist-off was reported with in-specification conditions. Root causes for failures induced by out-of-specification circumstances could be well explained. The respective recut rates of the new connection designs were found to be lower than those of the existing ones. A comprehensive field test program on two newly developed high-strength BHA connections will be presented. The measured key performance metrics, which could not be covered in laboratory experiments and were particularly evaluated in client wells, will be discussed. Investigation results of failures caused by out-of-specification conditions will be shared. The field trial results indicated that the two new connection designs provide a reliable solution to twist-offs of existing API connections induced by harsh fatigue environments.