Air-lift characteristics of rock core mass in gas–liquid–solid mixed flow

Abstract

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9, the maximum liquid-phase superficial velocity is increased by 109% compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation.