Perpustakaan Digital ITB

Cuttings settled on the low side of deviated well sections produced by drilling through a deviated well section frequently lead to higher torque and drag, a risk of developing stuck pipe situation and higher equivalent circulating density (ECD), all of which can cause difficulties in maintaining wellbore stability and raises the cost operations. To explore this systematically, a detailed 1:60 scale CFD modelling of the drillstring, annular gap, and bit face was carried out using recent peer review literature in which a 3D model with specific three nozzle at the bit. With a poly-hexcore mesh refined in the region, specific mesh value for nozzle exits and inner wall bit, simulations of incompressible water with no slip wall boundary assumptions were run with inlet velocity specified based on flowrate 200 to 400 GPM, a rotating wall boundary condition at the bit face was applied to the drillstring to model its rotational effect during drilling. By using the CFD software, convergence was checked when residuals reached 1E-03 and the output of pressure drop and the outlet velocity converged. Sensitivity analysis of five nozzle designs found a trade-off situation to the parameters that a small orifice yielded the greatest jet momentum and hydraulic horsepower but were excessively high in required pump pressure and had poor efficiency and in this simulation method, it is assumed no cuttings model is created. Conversely, the largest orifices had minimal pressure drop but were incapable of velocity to transport cuttings reliably. Three 12/32” nozzles at a flowrate of 300 GPM were identified as the ideal configuration, with the outflow velocities that exceeded the critical cuttings velocities (0.79 m/s), the pressure drop did not rise above 60% of pump capacity and the hydraulic efficiency were 65%, therefore creating a well-balanced solution that will provide better hole cleaning in deviated well operations.