Axial Excitation Tools, or AETs, are known to help improve ROP in modern horizontal wells. These devices instigate an axial vibration in the drillstring, which then propagates along the length of the horizontal assembly. The improvement in ROP is thought to originate from a more effective WOB transfer due to this induced axial movement from the AET. However, the exact mechanics of how these tools affect the drillstring is not known due to a lack of adequate modeling. Additionally, little work has been done to examine the potential consequences of inducing an axial resonance within the drillstring while utilizing these types of tools. This study explores these questions through advanced dynamic modeling.
Using a newly-developed, validated, comprehensive drillstring model, the dynamic response of the drillstring, due to the axial excitation provided by an AET, is examined via a forced-frequency approach. The resulting sensitivity analysis illustrates the dependence of the system on the various operational and structural characteristics of the drillstring. Parameters examined include applied WOB, wellbore trajectory, design characteristics of the AET, and various boundary conditions. Nonlinear time- domain simulations are also conducted in order to quantify how AETs affect the axial force transfer to the bit.
It is shown that various operational parameters will have a noticeable impact on the dynamic response of the drillstring when inducing axial vibrations while drilling. This observation suggests the necessity to properly plan for the use of AETs in order to avoid unnecessary failures of downhole components and subsequent non-productive time (NPT). While the modeling itself is advanced, the outputs are designed to help visualize the response of the system in a "user-friendly" manner, reducing the learning curve and bridging the gap between the "tech-savvy" and non-technical personnel.
This study presents an efficient way of determining the potential of harmful vibrations when drilling with an Axial Excitation Tool. The modeling approach shown is comprehensive and provides new insights into the fundamental operation of these types of tools and how axial excitations help to improve drilling efficiencies. Results presented show that induced vibrations do not simply "reduce friction," as is so often claimed; instead, these tools generate a dynamic axial force, oscillating about the average value, which may help work past "tight-spots" along the well. In turn, this would give the impression of reduced friction along the wellbore based on hook load measurements.