Annular Pressure Loss and ECD

This approximate calculation gives an idea of annular pressure loss, however this should just be used as a guide as it ignores variables such as, length of BHA, washouts in the open hole and solids loading or temperature changing the mud rheology. The the mud velocity is less than the critical velocity then the mud will be in laminar flow If the mud velocity is greater than the critical velocity then the mud will be in turbulent flow

Mud Specs Pump rate are used to determine whether the flow is Laminar or Turbulent

Laminar Flow $$ APL = \frac{\text{Depth} \times \text{yp}}{200 \times (\text{OD} - \text{ID})} + \frac{\text{pv} \times \text{v} \times \text{depth}}{1000 \times (\text{OD} - \text{ID})^2} $$

Turbulent Flow $$ APL = \frac{12.9^{0.75} \times v^{1.75} \times pv^{0.25} \times \text{Depth}}{1396 \times (\text{OD} - \text{ID})^{1.25}} $$

formula shown in Imperial form