CFD Modelling and Simulation of Drilled Cuttings Transport Efficiency in Horizontal Annulus During Gas Drilling Process: Effect of Gas Injection Method

Gas drilling, such as the air or nitrogen drilling, can improve the drilling efficiency and effectively protect the oil and gas reservoir from the lost circulation during the drilling process. However, a major disadvantage of the gas drilling is the severe deposition of the drilled cuttings, especially in the horizontal gas drilling, which mainly caused by the poor transport capacity of the gas phase due to its low density and viscosity. Generally, the solution is increasing the gas injection rate, but it will lead to a higher cost and may cause ice-balling of the drill bit. In this paper, a pulsed gas injection method is proposed to overcome the shortcoming, leading to cost reduction and efficiency increase. The Eulerian-Eulerian two-fluid approach with the kinetic theory of granular flow is employed to simulate the gas-solid two-phase flow in a 3D eccentric horizontal annulus using CFD modelling. The RNG k-e turbulence model is adopted to describe the turbulence behavior of the gas phase. The effects of various gas injection methods on the gas inlet velocity, pressure drop, cuttings volume fraction, granular temperature, turbulence kinetic energy, and turbulence dissipation rate are systematically investigated. The results show that almost no stationary cuttings bed is formed in the annulus under the pulsed gas injection condition. The cuttings particles are conveyed out within the wave-like moving cuttings bed. Compared with the constant-rate gas injection method, the pulsed gas injection method provides a much better cuttings transport efficiency at the identical condition of gas injection volume.