Resolving Torsional Vibration in Limestone Reservoirs Reduces Equipment Damage
Authors: Carpenter Chris 
Published: November 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19058, “Resolving Torsional Vibration in Horizontal Limestone Reservoirs Prevents Severe Equipment Damages,” by Adil Zahran Al Busaidi, SPE, Ahmed El Hawy, Ahmed Omara, Ali Baqir Al Lawati, Ramiro Oswaldo Vasquez Bautista, SPE, Muhannad Awadalla, and Ghaida Abdullah Salim Al Ghaithi, Schlumberger, and Zied Chibani, SPE, and Suroor Al Jamaei, Petroleum Development Oman, prepared for the 2019 International Petroleum Technology Conference, Beijing, 26–28 March. The paper has not been peer reviewed. Copyright 2019 International Petroleum Technology Conference. Reproduced by permission.
Torsional vibration (also known as stick/slip) is a major contributor to•equipment failure and severe damage•when drilling the 6.125-in. lateral limestone Shuaiba reservoir section. This paper examines multiple factors that can affect the severity of stick/slip and measures their actual effect. These factors include bit and bottomhole assembly (BHA) design and formation and mud properties. The authors examined the effect of using a software plugin to an automated drilling system to mitigate stick/slip when drilling the 6.125-in. lateral section.
Introduction
Before the deployment of rotary steerable systems (RSS) in the Shuaiba reservoir section, all directional sections (12.25-, 8.5-, and 6.125-in.) had been drilled with positive displacement motors (PDMs), but with the implementation of RSS, the operator achieved dramatically reduced well-delivery time. In the 12.25- and 8.5-in. sections, the shale and shallow limestone formations did not introduce any negative effect on drilling mechanics along with the change in the directional drive. In the lateral reservoir section (6.125 in.), stick/slip became more severe and resulted in higher costs. It was vital to identify the root cause of, and to implement preventative measures for, the damage.
Stick/Slip Factors
Controllable factors related to stick/slip in the bit/BHA design include type of drillpipe, the directional drive used, and stabilization. Fig. 1 shows a significant change in stick/slip behavior between two different bit designs in simulations.
Type of Drillpipe Used in Horizontal Drilling. In long lateral sections, drillpipes of 3.5 or 4 in. occupy most of the drillstring below the 7-in. liner hanger. Generally, the larger the size of the drillpipe, the higher the makeup torque limit. In terms of shocks and vibration, the purpose of having a larger drillpipe size is to stiffen the BHA and reduce the overall vibration of the drillstring. Upgrading to larger drillpipe size offers further improvement from a hydraulics perspective. The standpipe pressure drops because of the increase in the tubular inside diameter; furthermore, hole cleaning improves with larger pipe size.
Directional Drive (Motor or RSS). The two available directional-drive options in this application are PDM and RSS. The RSS is preferable for the long lateral section in this case. The RSS creates a borehole with a higher integrity because it does not create microdogleg severity. However, a PDM system is more reliable in delivering directional requirements quantitatively. The motor can generate a higher rate of penetration (ROP) than RSS tools, with a lower rate of surface rev/min.