Experimental And Theoretical Study On Drilling String Of Horizontal Well For Gas Drilling

The combination of gas drilling and horizontal well can effectively recognize and protect the reservoir, increase the drainage area and enhance oil recovery. However, there are problems and challenges in the key technologies about drill string motion state and well path control with gas drilling of horizontal wells or complex structure wells. Technical problems about drill string dynamics characteristics analysis and drag and torque calculation of horizontal gas drilling need to be solved urgently.Based on literatures about string dynamics of gas drilling and friction torque of horizontal wells at home and abroad, a series of work such as theoretical research, experimental study, simulation modeling and result analysis has been done. In this paper, experimental study has been done about motion state of drill string and friction torque of horizontal gas drilling. And nonlinear dynamic finite element model has been established through experimental result. Main achievements are as follows:(1) On the basis of similarity theory and model test, the relationship between the influencing factors are analyzed, and the relationship between the relevant parameters and the basic criterion are determined. According to the principle of similitude, a simulation experimental device for investigating drill string dynamics characteristics of horizontal well is set up.(2) The weight on bit (WOB) fluctuation of horizontal well is researched by simulation experiment. The frequency between the drilling string rotation and the WOB fluctuation is confirmed. The change of weight on bit to the effects of the WOB fluctuation frequency is analyzed. The change of the WOB and drilling string rotation speed would influence the WOB fluctuation.(3) For the field application of wells with structure of152.4mm, suitable WOB and rotational speed can ensure the proper WOB fluctuation and avoid severe vibration.(4) The experiment shows that the rotational speed would influence the torque. The relationship between the tangential velocity and the axial velocity would decide the torque. The rotation of drill string would reduce the friction, so rotary drilling should be used in gas drilling.(5) Influenced by gravity and friction, the drilling string is always in the low right part of the wellbore and the variation of the WOB and the rotary speed wouldn’t change this feature. In the horizontal there is no whirl phenomenon like the vertical well.