Study On Cuttings Transport Under Turbulent Flow Conditions In The Highly-deviated Eccentric Annuli

Horizontal well and extended-reach well have been widely used for the development of marine oilfield, mature oilfield and low permeable oilfield. However, during the process of drilling, cuttings will settle and eventually form a cuttings bed in the highly-deviated section when fluid velocity is less than the suspended velocity for cuttings. This lead to high friction and torque, slower rate of penetration, pipe stuck and other problems. In this study, turbulent flow of drilling fluid, incipient particle motion, and cuttings-transport behaviors are studied, and comparisons of predicted results and experimental data indicate the reliability of models.Structured mesh and sliding mesh are used to generate the flow zone and simulate the drillstring rotation, respectively. The Realizable k-ε model and SIMPLE method are chosen to simulate fluid flow in the different horizontal annular structure. Comparing experimental data and predicted results, the slot method or lamb approach as the equivalent diameter is more accurate for predicting the friction loss in the annuli.Considering the net weight, lift force, drag force, fluid flow pressure, adhesive force and additional mass force acting on the particle, particle random distribution function and wall law theory are introduced to develop a mechanical model for sliding, rolling and lift method in the highly-deviated section. The results show the drilling fluid rates required by the rolling and lift gradually increase, and the rates decrease with the increase of cuttings-bed height. Therefore, bed height can be predicted for a known rate based on the above conclusions.Based on the Euler solid-fluid model and Realizable k-ε model, cuttings-transport behaviors with pipe rotation under turbulent flow conditions in the highly-deviated eccentric section are simulated. The numerical simulations indicate the cuttings bed is inclined when drillstring is rotating, and the bed presents in an asymmetric distribution in the annuli. Also, pipe rotation can reduce cuttings concentration and solid-fluid pressure loss, but their ranges are dependent on inclination, cuttings injection concentration, particle size, drilling fluid velocity and viscosity. However, after a certain rotation speed, no additional contribution is observed. And the empirical expressions for the cuttings concentration and solid-fluid pressure loss are developed based on the numerical results.