Hardware-In-the-Loop Simulations Used as a Cost Efficient Tool for Developing an Advanced Stick-Slip Prevention System

Abstract

Hardware-In-the-Loop (HIL) simulation is a technique where machine control software runs virtual machines, which are mathematical models emulating the physical machines. The technique has become increasingly popular in recent years, because of its ability to shorten product development time for complex dynamic systems, through quick and cost efficient testing over a wide range of conditions. This paper focuses on the lessons learned from HIL simulation testing of an advanced and patent applied method for curing and preventing stick-slip oscillations in drilling. In this project the HIL simulations have provided several advantages, such as a high repeatability in test conditions, the ability to test under challenging conditions rarely occurring in the field, thus avoiding time consuming field tests. The HIL simulations have also proven to be an efficient tool for debugging the control software, because programming errors are discovered long before the commissioning and field test phases. The HIL simulation of stick-slip oscillations uses an advanced dynamic model for the entire rotary system, including the top drive electronics, the motors, and the drillstring. The drillstring is modeled as a series of lumped inertia and torsional spring elements where the friction torque for each element is a non-linear function of the wellbore contact force and instant rotation speed. The lowest element also includes the bit torque as a function of weight on bit. The first version of a stick-slip prevention system, which has been described in an earlier IADC/SPE paper, was HIL tested over a wide range of drillstring and well geometries. Simulations with very long strings (typically 5000 m or longer) revealed that higher mode stick-slip oscillations tend to appear when the normal stick-slip oscillations are cured. The second mode frequency is roughly three times the frequency of the fundamental mode so it falls outside the effective absorption band for the first version prevention software. However, after adding an inertia compensating term in the tuned speed controller, the stick-slip prevention software was able to prevent both the fundamental and the higher modes stick-slip oscillations at the same time. In summary, the HIL simulations improved the stick-slip prevention system so it is more robust, easier to operate and has improved performance. The HIL simulations also helped to find and eliminate code bugs.

Field Experience with an Active Stick-Slip Prevention System

“…As presented in a recent paper by Kyllingstad and Nessjøen (2010), 2 nd mode stick-slip is a phenomenon observed in simulations and HIL-testing, especially prevalent in longer drill strings. Field loggings have now also verified that this is not only a theoretical phenomenon, but a real problem that needs to be addressed when using an active stick-slip prevention system.…”

“…Kyllingstad and Nessjøen (2010) describe the theory of this feature. It is designed to improve the top drive's ability to prevent both first and second mode stick-slip.…”

Drilling seeking automatic control solutions

“…Automatic stick slip prevention by feedback control of motor current and speed is presented e.g. in (Kyllingstad and Nessjoen, 2010).…”