Analysis and Control of Stick-Slip using a Scaled Experimental Drilling Rig

Abstract

Drilling is one of the most challenging and expensive processes involved in oil and gas production. Due to the destructive nature of the drilling process, dysfunctions are common during drilling. These dysfunctions can increase the non-productive time (NPT) greatly, cause loss of revenue and pose a safety concern. Avoiding and controlling these dysfunctions is essential for safe and efficient drilling. Friction from the wellbore and the rock formation induces vibrations in the drillstring. The drillstring vibrations can be classified into three modes: axial, lateral and torsional. Stick-slip vibrations are a type of torsional vibrations which occur very frequently during drilling. These vibrations are responsible for decreasing the rate of penetration (ROP), causing damage to the drilling equipment and greatly reducing the life of a drill bit. Different control algorithms have been proposed in the last few decades but only one of them (Shell Soft Torque) has seen industry-wide adoption. Now, with the increase in the complexity of well design and increasing depths, the limitations of Soft Torque have been highlighted. Therefore, extensive research is still underway to design a new stick-slip con-trol/mitigation approach. The main aim of this study was to analyze and control stick-slip vibrations in a drillstring using a downscaled experimental drilling rig setup. To achieve this, an experimental setup was designed and constructed. Thereafter, strategies to control/mitigate stick-slip were devised and tested on the constructed setup. The results showed that surface parameters alone may not be sufficient to design a robust stick-slip mitigation system. Access to downhole data, even at low frequency, can significantly help in the development of a stick-slip mitigation system.