Design And Analysis Of The Hydraulic Thruster Used In Horizontal Wells

In the process of horizontal well drilling，with the increase of the deviation angle, the component forceof the weight of the drill string in horizontal direction is getting smaller and smaller, and the frictionalresistance between the drill string and the borehole wall is increasing correspondingly. So it is oftendifficult to exert WOB by the weight of the drill string. The way of using hydraulic thruster to generateWOB can absorb the vibration of the drill bit, and also the value of WOB is unaffected by the friction.Therefore, the hydraulic pressure is widely used in horizontal well drillingThe paper puts forward the design idea of nested hydraulic thruster on the basis of full investigation ofthe related work at home and abroad. The new design can make full use of the inner space of all levers ofpiston shaft. When the stage number of piston, the number of stroke, and the stroke distance are equivalentto the existing hydraulic thruster, the new design can greatly decrease the overall length of thruster; reduceits manufacture difficulty and cost. Theoretical calculations and numerical simulation are used to optimizethe fit mode and materials of the torque transmission mechanism of hydraulic thruster, it is found thattetragonal fit and hexagonal fit cannot meet the strength requirements and stiffness requirements within thedimension parameters of the design. During the operation of octagonal fit, sliding friction force between thesleeve and the piston shaft to meet the WOB requirements. Strength, stiffness and WOB requirements aresatisfied simultaneously by spline fit. So the spline fit is chosen as the torque transmission mechanism ofhydraulic thruster, whose dimensions of different stage piston shafts are determined by numericalsimulation. A kind of three-stroke hydraulic thruster is designed based on numerical simulation, which issuitable for the borehole of215.9mm or more. Theoretical calculations show that the hydraulic thruster canprovide26.59KN~126.93KN WOB for the bit in the drilling process. It fully meets the WOBrequirements. This paper offers a new method for the design of hydraulic thruster for horizontal wells.