Numerical Simulation for Cuttings Migration during Gas Drilling of Horizontal Wells

To enhance the hole-cleaning performance during gas drilling of horizontal wells, research has been conducted for characteristics of cutting migration in horizontal sections. Based on the gas-solid flow model, the migration characteristics of single-particle cuttings and multi-particle cuttings were simulated using FLUENT at different diameters, gas injection rates, rotating speeds and eccentric distances of drillpipe. The results showed that in a horizontal annulus, single-particle cuttings mainly migratedin saltation, while multi-particle cuttings migrated in creep and saltation. For the gas injection rates of 50 m3/min, 70 m3/min and 90 m3/min, the first saltation distances of 5mm diameter cuttings were 0.55 m, 0.90 m and 1.50 m respectively. For the gas injection rate of 50 m3/min, 1.5 mm diameter cuttings’ first saltation distance is 1.5 times of 3.0 mm diameter cuttings.For the rotating speeds of 0 r/min and 60 r/min, the third saltation distances of 7.0 mm diameter cuttings were 0.43 m and 0.62 m respectively under the gas injection rate of 50 m3/min. For the eccentric distances of 0 mm, 10 mm and 15 mm, the second saltation distances of 6 mm diameter cuttings were 0.55 m, 0.44 m and 0.28 m respectively under the gas injection rate of 50 m3/min. Therefore, the faster gas injection rate, the smaller diameter of cuttings, the faster rotating speed and the smaller eccentric distance, the further would cuttings be removed. Taking measures such as improving gas injection rate appropriately, installing a hole cleaning device for horizontal well and moderating drilling pipe could benefit the hole cleaning efficiently.