Research On Downlink Communication Ground System In Strapdown Rotary Steering Drilling System

As an important part of the downlink communication systems,the ground downlink communication system play a key role in controlling the trajectory of drilling,guide the drill bit to achieve the target and so on.Currently the downlink communications technology is monopolized by several major foreign oil service co MPanies,domestic experts also conduct some researches on the downlink communication theory,the downlink coding and other related technologies,but their researches mostly remain on theoretical exploration stage since lacking of appropriate rotary steerable tool as a background.In this paper,the research is depend on the "Strapdown rotary steerable drilling tool",which is independently developed by the Drilling Technology Research Institute in Shengli Petroleum Administration,provide a technical basis and equipment for ground downlink communication system.This paper analyses the bypass drained downlink communication principle and the design parameters of ground systems,raise a design of downlink communication ground system based on this principle and design parameters,then describes the composition structure and the key design of the downlink ground systems.According to the design scheme of ground system for downlink communication,a new ground downlink device was designed.The device was composed of two parts: pneumatic control valve and decompressive device,in which the valve element of the pneumatic control valve was in rotary valve structure and the decompressive device was in reconfigurable orifice structure,offering different configurations for different wellhead pressures and bypass flows.Based on the structure design of this device and with the combination of theoretical analysis and analogue simulation,this paper first made a theoretical analysis on the influence of the structure parameter of decompressive device on the downlink signal,then probe into the relation among the throttle pressure drop,flow rate and opening angle of the rotary valve of the pneumatic control valve,and finally set up an analogue simulation model for the control valve structure and decompressive module,which gave integrate analyses on the flow filed characteristics of the ground downlink device under different working conditions.The required downlink control information of the strapdown rotary steering tool was confirmed,and the encoding structure of the downlink information was designed.which uses sync header and check bit to further improve the encoding reliability;the probability of code element was analyzed,bringing up an encoding method of downlink information based on Hoffman coding,making a co MParative analysis on the encoding efficiencies,advantages and disadvantages between binary coding and Hoffman coding,and finally,developing the software control system of downlink communication combining binary coding and Hoffman coding,which met the control requirements of the ground downlink device.An experimental prototype of downlink communication ground system was designed and developed,and some relevant ground experiments were also completed with it.Results showed: measurements of bypass flows and pressure drops of the ground downlink device were consistent with the simulation results,which indicated the design of ground downlink device was correct.It could be seen from the received information in the turbine generator of the strapdown rotary steering tool that the wave characteristics of downlink information were pretty clear and the encoding results were correct,which verified the feasibility of the encoding method of downlink information and the correctness of the proposed design scheme of downlink communication ground system.