Dynamics study of self-Pulling & self-Rotating jet drill bit in natural gas hydrate reservoirs radial horizontal well drilling

Abstract

Deep-sea natural gas hydrate is rich in resources and has high energy density, making it a clean energy source with great development prospects, compared with the conventional oil and gas formations, hydrate reservoirs are shallow, with low hardness and uniaxial compressive strength. However, due to temperature changes, conventional drilling can cause hydrates to decompose, leading to wellbore instability, which will lead to wellbore instability. In view of the problem of increasing the rate of penetration (ROP), horizontal wellbore formed by high pressure jet is considered an efficient method for natural gas hydrate drilling, and the drill bit is the core equipment to form horizontal wellbore in the reservoir. Therefore, a self-pulling and rotating drill bit is proposed, the basic principle of that is when the drill bit breaks the rock at the bottom of the well, the front nozzle provides jet rock-breaking energy, the rear nozzle generates rotational torque, overcoming the friction torque between the rotating drill bit and the shaft, providing rotational energy for the drill bit, realize the movement of self-rotating and move forward while drilling. Therefore, three parameters are mainly evaluated in this paper, the self-pulling force, the angular momentum and jet pressure, the self-pulling force is for the forward moving of the bit, the angular momentum is for the stable rotating of the bit, and the jet pressure is for the natural gas hydrate drilling. Meanwhile, three different structural bits are analyzed from the influences of inlet flow, outlet size on the self-pulling force, jet pressure and flow ratio of front and rear nozzles. The results demonstrate that self-pulling force and jet pressure of bit with four front nozzles is the best at the same conditions, and the flow ratio of front and rear nozzles is depended on the structure of the bit; with the increasing of the inlet velocity, the self-pulling force and the jet pressure increases nonlinearly, and the angular momentum increases linearly. The equivalent outlet size has remarkable influence on the jet pressure, with increase of the front and rear nozzle size, the self-pulling force and jet pressure is decreases greatly. Moreover, the wellbore hole forming ability of the jet bit under different jet distances is discussed, shows that erosion wellbore hole forming ability is best at the nozzle outlet. This research provides an effective and feasible solution for the drilling of the hydrate radial horizontal wells.