Study on speed characteristics of hydraulic top drive under fluctuating load

A hydraulic top drive is a high-power gyrator used in oil or scientific drilling rigs, whose shaft is connected to drill pipe when it drives drilling tools to excavate well. The output speed of top drive determines the speed of drill bit directly. Load acting on the top drive shaft fluctuates randomly, which will cause top drive output speed hard to be in consistent with the setting value. This paper presents a main transmission system of a hydraulic top drive designed for deep continental scientific drilling, which was built with a multi-stage mechanical structure and a closed circuit hydraulic system with variable displacement pumps and motors. Electro-hydraulic proportional control was applied to vary the speed of the hydraulic top drive. A theoretical model is detailed for the hydraulic top drive main transmission system. Among the new techniques proposed in this paper is a simulation model for studying the performance of hydraulic top drive and capturing speed characteristics under fluctuant load. A drilling experiment of the hydraulic top drive was performed on the CRUST-I drilling rig in CCSD-SK-II well site. This paper concludes by comparing the results of the simulation model with theoretical results and drilling experimental data gathered in the hydraulic top drive possessing the same architecture, components, and control methods used within the simulation model. The drilling experiment and the analysis result showed that the hydraulic top drive could meet the requirements of deep continental scientific drilling and that the speed could be output according to the setting speed with very small oscillation. The simulation model can be used for several applications such as hydraulic top drive design and performance analysis of various drilling conditions.