Mechanical Behavior and Comprehensive Optimization Design of Drill String with Drag Reduction Oscillators in Horizontal Drilling

Abstract

Abstract The efficiency and safety of drilling operations have increasingly been limited by the friction and torque of the drill string in horizontal wells. Drag reduction oscillators have shown in practice to efficiently lower the drill string's friction force, accelerate rate of penetration, and raise the extension limit. Nonetheless, there is still more to explore on the drill string with drag reduction oscillators’ mechanical behavior and thorough optimization design. The primary objectives of this paper are stick-slip suppression efficiency and drag reduction efficiency. Taking into account the strong nonlinearity of the friction force and introduction of definite conditions, the model of drill string with drag reduction oscillators is established. Taking into account the torque loss and rotary speed control, the stick-slip vibration model with oscillators is also established. By using an orthogonal test design, the key determinants influencing the stick-slip suppression efficiency and drag reduction efficiency were identified, along with the propagation distance model and the optimal installation location model. Furthermore, the optimal drag reduction parameters and stick-slip suppression parameters are recommended, taking into account drill string buckling, fatigue failure, and hydraulic loss. All the above approaches were utilized in China Jimsar oilfield. The results demonstrate that the oscillator can efficiently decrease friction force while improving the WOB. The proximity of the oscillator to the drill bit directly correlates with the efficiency of drag reduction. The efficiency of drag reduction is mostly affected by the number of oscillators and the corresponding amplitude, while stick-slip suppression performance is primarily influenced by the rotational speed and WOB. Increasing the rotational speed has greater impact on preventing stick-slip than decreasing the WOB. In this case, it is advisable to install three oscillators with an amplitude of 40 kN, which increases the efficiency of drag reduction by 37.5%. When the optimum rotation speed is 162 r/min and the WOB is 171 kN, the efficiency of the stick-slip suppression is improved by 12.1 %. This study has significant implications for the risk control in horizontal drilling operations and the optimal design of oscillators.