Effect of hole shape on roughness friction factor in perforated and slotted horizontal boreholes used for opencast mine dewatering

Abstract

Horizontal boreholes were adapted for using in mine dewatering systems. Efficient and economically sound application of this new method of dewatering requires using perforated or slotted pipes as filters when installing casing. Pressure drop along a horizontal borehole is a major factor that affects the borehole performance. The pressure drop is caused by four separate effects: wall friction, perforation roughness, inflow acceleration, and mixing effects. This paper is devoted to studying the effects of these two former factors in perforated or slotted pipes. Numerical analysis was carried out using different types of perforation holes and slots. The simulation model was constructed using ANSYS Fluent 14.5 software. The results showed that at high Reynolds number, roughness friction factor values in perforated pipes with circular holes are significantly higher than those in slotted pipes with axially elongated slots and slotted pipes with perpendicular (to pipe axis) slots.

Keywords

• perforation roughness
• horizontal filters
• dewatering
• opencast mines