A Method of Evaluating the Effectiveness of a Hydraulic Oscillator in Horizontal Wells

Bent-housing motor is the most widely used directional drilling tool, but it often encounters the problem of high friction when sliding drilling in horizontal wells. In this paper, a mathematical model is proposed to simulate slide drilling with a friction reduction tool of axial vibration. A term called dynamic effective tractoring force (DETF) is defined and used to evaluate friction reduction effectiveness. The factors influencing the DETF are studied, and the tool placement optimization problem is investigated. The study finds that the drilling rate of penetration (ROP) can lower the DETF but does not change the trend of the DETF curve. To effectively work, the shock tool stiffness must be greater than some critical value. For the case study, the best oscillating frequency is within 15∼20 Hz. The reflection of the vibration at the bit boundary can intensify or weaken the friction reduction effectiveness, depending on the distance between the hydraulic oscillator and the bit. The optimal placement position corresponds to the plateau stage of the DETF curve. The reliability of the method is verified by the field tests. The proposed method can provide a design and use guide to hydraulic oscillators and improve friction reduction effectiveness in horizontal wells.