Transport Cuttings

Transport cuttings•The well is drilled and cuttings are produced the must be removed from the well
•The drilling fluid is circulated down through the pipe and bit nozzles entraining the cuttings and carrying them up the annulus to surface

•Cuttings removal is a function of cuttings size, shape and density; rotation of the drillstring; and mud properties such as viscosity, density and annular velocity
•Viscosity describes the rheological properties of the drilling fluid
–Cuttings settle faster in low viscosity fluids
–Higher viscosity fluids improve cuttings transport
–Most drilling fluids are thixotropic meaning that they gel under static conditions

•Velocity refers to the annular velocity of the fluid–Generally the higher the annular velocity the better cuttings removal
–If velocity is too high then turbulent flow may occur resulting in less efficient cuttings removal and possible wellbore erosion
–The net velocity is the difference in the slip velocity of the cuttings and the annular velocity
•Transport velocity=Annular velocity -slip velocity

Cuttings transport in high angle wells is more challenging than vertical ones
–Cuttings tend to accumulate at the low side of the hole creating cuttings beds
–The use of thixotropic fluids with high Low-Shear-Rate Viscosity run in Laminar flow can help clean out these cuttings beds
–High flow rate and thin fluid to try and achieve a turbulent flow can keep these wells clean
–Generally a mixture of high LSRV fluids and thin turbulent fluids are required to keep the hole clean

•High density fluid sweeps aid in hole cleaning
–The higher density fluid tends to get into the smaller cuttings beds and push them into the higher section of the hole to be cleaned off
•Pipe rotation
–This helps stir up the cuttings and lets the fluids take them away