Analysis of the Stick-Slip Phenomenon Using Downhole Drillstring Rotation Data

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe stick-slip phenomenon has been identified in the industry as an inefficient and often damaging drilling vibrational condition. Numerous studies, predominantly focusing on measurements of drillstring torque, have detailed the nature of this phenomenon, and have shown its detrimental effects on drillstring components and especially on PDC bits. Using surface rotary motor current, drilling contractors and surface logging companies have attempted to monitor drillstring torque so as to recognize and correct for this torsional instability.Recent MWD tool developments using downhole drillstring rotational speed have established a superior method to identify stick-slip and establish its severity. Measuring actual rotational behavior of the lower BHA gives a better insight to the torsional movement of the drill bit during the drilling process, without the problems involved when inferring this behavior from the surface torque readings, obtained at the opposite end of the drillstring. This paper describes the method of determining the stickslip behavior downhole from magnetometer readings. The sensors are sampled at a high enough frequency to compute nearinstantaneous values of downhole drillstring rotation, and variations in the RPM are then used to establish the incidence and severity of stick-slip. This information is telemetered to the surface and provided to the driller in order to allow for real-time changes in drilling parameters to correct for this inefficiency. Also presented in the paper are several examples using actual field data that detail stick-slip behavior and demonstrate how real-time information about downhole RPM variations can help to reduce the problems associated with this torsional drilling dysfunction.

Application of Rotary Steerable System/PDC Bits in Hard Interbedded Formations: A Multidisciplinary Team Approach to Performance Improvement

“…In the analysis all incidents were noted and explained by looking at the bit type, drilling parameters, BHA configuration and formations drilled. 6 Here is a typical example of an analysis, in this case carried out on the first run with new BHA and new design antiwhirl PDC bit: Lateral vibrations also remained low throughout the run, averaging 1.0 g-RMS. The lateral vibrations experienced seemed to be caused by coupling with torsional vibration.…”

The Significance of Pro-active Online Monitoring with Stick-slip Mitigation

“…Mud motor stalling may cause backward rotation of the BHA, leading to extreme torsional vibration (Efteland 2014). Robnett (1999) and Makkar (2014) report backward rotation causes severe damage to the PDC cutters. Another driver for stick-slip is high torque and drag along the wellbore, from the BHA and up to the surface.…”

Derivation and experimental validation of an analytical criterion for the identification of self-excited modes in drilling systems

“…Several studies have focused on stick/slip of the whole drilling system, the most familiar kind of measured torsional vibration [11,14,15]. In this context, the drilling systems comprises the rig, a drillstring, and a bottomhole assembly (BHA) with measurement tools, and a bit to cut the formation.…”