Design and Numerical Simulation on New Type Near-Bit Hydrocyclone for Downhole Solid-Liquid Separation

Solid phase is an important component of drilling fluid, but when drilling fluid with high solid content is injected to well bottom, it leads to decrease in rate of penetration (ROP) and waste of drilling energy. Therefore, it is an economic method to add solid control equipment near bit to achieve solid removal of bottom-hole drilling fluid. Based on hydrocyclone separation technology, this paper presents a new near-bit hydrocyclone (NBHC) installed with guide vanes for downhole solid-liquid separation. Structure and separation mechanism of NBHC are introduced. This tool can separate part of solids contained in drilling fluid into wellbore annulus in advance, especially plugging particles. In this way, the solid content of drilling fluid flowing into bit will reduce, thereby the bit rock-breaking environment will improve and ROP increase. Firstly, the Euler multiphase flow model is adopted to simulate the NBHC for phi 311.2 mm wellbore. The results indicate that NBHC has a strong ability of drilling fluid solid separation, and the mass separation efficiency reaches 79.30%. Then, the effects of nozzles diameter, mud flow rate, solid volume fraction and solid size on the separation efficiency and pressure drop of NBHC are studied by simulation. Results show that the separation efficiency is positively correlated with nozzles diameter and solid size, negatively correlated with solid volume fraction, but not significantly correlated with inlet mass flow rate. It is proved that appropriate structural parameters help to further improve the working performance of NBHC, and it is an effective way to increase the ROP indirectly.

Automated summary

Solid phase is an important component of drilling fluid, but a high solid content can lead to decreased rate of penetration and waste of energy. This paper presents a new near-bit hydrocyclone (NBHC) for solid-liquid separation based on hydrocyclone technology. The NBHC can separate solids, especially plugging particles, from the drilling fluid, reducing the solid content that flows into the bit and improving the rock-breaking environment and rate of penetration. Simulation results show that the NBHC has a strong solid separation ability, with a mass separation efficiency of 79.30%. The study also analyzes the effects of various parameters on the separation efficiency and pressure drop of the NBHC.