Cost Savings through an Integrated Approach to Drillstring Vibration Control

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrillstring vibrations occur frequently during drilling operations. They can result in drillstring failure, fishing and, in the worst case, side tracking. At the same time, the rate of penetration and the bit/downhole tool longevity are reduced. All these effects of drillstring vibrations lead to substantial additional well cost.An integrated approach towards vibration control, addressing all the contributing factors, can have a positive impact on well costs. This is especially true for hard rock drilling, as frequently occurring in Middle East countries. Various types of vibration can be distinguished, each having their own specific adverse effects. The integrated approach, developed in Shell, consists of the following elements: 1. The application of a soft torque rotary system (electric and hydraulic rotary drives) for suppressing (torsional) stick slip vibration of BHA and bit. 2. The use of vibration analysis software in the design of a BHA, to prevent buckling and to identify safe operating windows for rotary speed. 3. The cost-effective deployment of vibration monitoring tools. 4. The regular inspection of drillstring components.Field cases of the deployment of this methodology reveal that twist-offs can be reduced by more than 80% and drilling performance in terms of ROP and bit life can be improved. Cost savings are realised through the reduction of well days and prevention of tool failures. A limitation of the method is that safe operating parameters are not available under all circumstances.

Mitigating Stick-Slip in Deep Drilling Based on Optimization of PDC Bit Design

“…1, left) that can severely damage PDC cutters. Such vibrational issues have long been tackled in the field via efficient integrated approaches [24] and specific solutions have been developed to mitigate stick-slip, according to four main trends: definition of best drilling practices to avoid the unfavourable regime of stick-slip [1]; surface regulation systems designed to absorb upward torsional waves [39,25]; hardware solutions to reduce friction along the drillstring [14,2]; hardware technologies aiming at controlling the penetration of the drillbit into the rock [8,20]. However, stick-slip still occurs today in a wide range of drilling applications [27].…”

Advantages of an LQR Controller for Stick-Slip and Bit-Bounce Mitigation in an Oilwell Drillstring

“…Many such controllers have practical limitations. However, one system that has achieved real-world acceptance is the soft torque rotary system (STRS) [16][17][18]. STRS is a torque feedback at the top of the drillstring which makes the system behave in a "softer" way rather than as a fixed heavy flywheel, so that the torsional waves arriving at the surface are absorbed, breaking the harmful cycling motion.…”

Fatigue life improvement of threaded connections by cold rolling

“…These new drilling techniques have placed even more demands on the drillstring, which has basically remained of the same design throughout its history. Downhole failure of the drillstring is an expensive and all too common occurrence which costs the industry millions of dollars each year [1,2]. The majority of drillstring failures are recognized and attributed to fatigue of the threaded connections, which join together the lengths of drillstring.…”