No abstract

In the paper the road vehicle simulation package Janus, developed in the Engineering Department at Durham University, is described. Janus is a flexible simulation package that allows internal combustion engine vehicles, electric vehicles and hybrid vehicles to be simulated, and their performance and energy consumption evaluated over standard driving cycles. The simulation techniques used in these programs are described and the simulation program shown to produce results comparable with experimental data.

No abstract

This paper describes the work carried out at NOV Downhole on an in house designed and built, small scale, vibration test rig which was developed with the purpose of replicating stick slip and studying various stick slip mitigation methods.There are currently well established down hole tools that offer improvements axial friction reduction and axial load transfer by way of introducing axial excitation into the drill string -with resulting improvements in ROP and MSE.As a result, such tools also have the potential for stick slip mitigation, by providing friction reduction particularly during the stick phase of stick slip where the string becomes stationary. This approach offers further ROP and MSE benefits where stick slip is prevalent.The introduction of axial excitation into the drill string compliments other stick slip mitigation devices such as the asymmetric stabilizer. The asymmetric stabilizer tackles the spin up phase of stick slip (by providing additional torsional damping) whilst axial excitation tackles the stick phase.During the rig testing, it has been possible to compare the axial excitation tool performance with that of a test with no Axial excitation tool present. The rig tests demonstrate significant stick slip mitigation with the axial excitation tool present. The axial excitation frequency used during the rig tests has been representative of that used by typical axial excitation tools. Axial load amplitude was similarly representative.Full scale field operations where an axial excitation tool technology has been applied have resulted in significant overall improvements in stick slip. With reference to offset data, the paper presents actual field data that demonstrates significant benefits to slip stick, lateral vibration, ROP and MSE and the resultant beneficial impact upon drill string tool and bit life.

For years drillers have been taught to mitigate all vibrations in the drillstring while drilling to maximize Rate of Penetration (ROP), limit bit damage, and extend bit life. While limiting lateral vibrations and stick/slip are proven ways to improve performance and maintain directional control, in recent years it has been conclusively proven in the field that inducing axial agitation with specialized downhole tools can significantly improve lateral reach. Currently, however, the benefits of downhole oscillation tools have not been thoroughly studied for other performance gains, such as improved ROP in non-directional wells.An extensive research study, including lab and field testing, found that a low-frequency, benign axial vibration can increase the ROP significantly in all well types. Initial laboratory experiments were performed by inducing axial vibrations into the drilling process on a small scale drill bit in hard rock. Dramatic improvements in ROP and drilling efficiency were observed, with the added benefits of improved bit life and an unexpected reduction in stick/slip. This lab experiment was later tested in the field by utilizing a proven downhole oscillation tool in an active Bottom Hole Assembly (BHA) to create the effect that was simulated in the lab. The field tests showed the same results as the lab tests: significant performance gains were observed in several test wells using the downhole oscillation tool as compared to offset data. In addition, this same downhole oscillation tool showed drastically improved directional control when run above a Rotary Steerable System (RSS) tool, and stick/slip was practically eliminated with no negative effect on bit life or BHA reliability.High-speed sensor data collected at the bit during both the lab and field tests will further demonstrate the validity of the theory. Testing for a hard-rock application with roller cone bits is forthcoming, as the data indicates possible performance gains in this environment as well.Overall, the study revealed many benefits, such as improving well placement, reducing Non-Productive Time (NPT) and time to Total Depth (TD) by preventing BHA component damage through beneficial axial vibrations from the downhole oscillation tool. The data indicates that "benign vibration" can drastically improve drilling performance. Induced Vibration Theory and Application Background (Forster and Grant, 2012)Theoretically, any drilling assembly which provides a fluctuating axial load application focused downhole will improve drilling efficiency. The axial excitation will improve drilling efficiency by breaking static friction, both in the BHA and at the bit. Once static friction is overcome and stead-state dynamic friction results, the Weight on Bit (WOB) required will be a fraction of the WOB required under normal drilling conditions, and load transfer will improve.