Evaluation of Lateral BHA Twist-Off Incidents and the Effect of a Redesigned Thread Connection on Reducing Twist-Off Risk in the Permian Basin, USA

Abstract

A common issue encountered when drilling in the Permian Basin involves the twist-off of a bottomhole assembly (BHA) component. A twist-off incident can result in significant costs incurred due to nonproductive time (NPT) as well as lost-in-hole (LIH) charges if retrieval of the fish is unsuccessful. The paper will present several case studies to illustrate the primary cause of the failures. An innovative thread connection for BHA components was designed in 2016 to reduce risk of twist-off. The paper will demonstrate its effect on reducing twist-off risk as well as the enablement of improved drilling performance in 2019. The paper will illustrate statistical analysis of data gathered from 2016 through 2019 comparing the performance of the conventional thread connection versus the new thread design. The goal of the analysis is to evaluate whether the thread design is effective in reducing the frequency of twist-off incidents. The bending moment of each connection within the BHA will be analyzed using modeling software to understand the stress-loading profile. Memory data from the rotary steerable system (RSS), including near-bit attitude measurements and downhole drilling dynamics, will be analyzed in conjunction with data acquired from the rig's surface sensors to identify if any abnormal drilling events are observed prior to the twist off. The BHA bending moment study concludes that connections between the measurements-while-drilling (MWD) tool and the RSS suffer higher stress loading compared to other connections in the BHA. Empirically, field statistics confirm that the connections between RSS and MWD exhibit the highest frequency of twist-off incidents. However, further analysis is required to understand the root cause of the connection failure. The memory data retrieved from the RSS enables the visualization of hole curvature and vibration at the time of the incident. Investigation into several field cases concluded that, immediately prior to connection twist off, there is sudden change in borehole curvature and/or emergence of shock and vibration (S&V) which can dramatically reduce the expected fatigue life of the connection. Based on the statistical analysis, it can be concluded that the new connection design is effective in reducing the twist-off failure rate of the BHA. Consequently, the implementation of the new thread design enabled a step-change in drilling performance through use of a more powerful positive displacement motor (PDM) to drive the RSS system.