Reynold Number for Drilling Hydraulics

Reynold number is the important figure because it demonstrates the flow regimes of drilling mud as laminar, transition or turbulent flow in annulus of the wellbore. In order to correctly calculate the Reynolds number, you need to use the effective viscosity, µea, which we already discuss about it from the previous topic.

The following equation is for Reynolds number in the annulus.


Rea = Reynold Number in the annulus

Va = Annular velocity, ft/min

Dh = Diameter of wellbore, inch

Do = Outside Diameter of tubular, inch

W = mud weight, ppg

µea = effective viscosity in the annulus, centi-poise

na = power law constant

For more understanding, please following this example, Reynold number calculation.

Va = 6 ft/min

Dh = 8.5 inch

Do = 5 inch

W = 9.5 ppg

µea = 42.53 centi-poise

na = 0.514

Rea = 3,781

The next topic will demonstrate you how to relate the Raynold’s number into flow regime.

Reference:  Drilling Hydraulic Books

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9 Responses to Reynold Number for Drilling Hydraulics

  1. Reben says:

    how we can know yeld point and plastic vescosity?

    • Hi Reben,

      Please find the answer below.

      Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm

      Yield Point (YP) = Reading from a viscometer at 300 rpm – Plastic Viscosity (PV)

  2. Engr. Moin Uddin Ahmed says:

    How recover the core sample (fully sand ) from the depth 500ft to 700ft ?

  3. curtis byram says:

    I was looking at your example calculation. you list the annular velocity in the formula with dimentions of ft/minute but your example data in listed as ft/second. is that a whoops.

  4. Matt Glover says:

    Hey folks at DrillingFormulas,

    I’ve been using your formula above to try and build an excel calc.

    But i get the answer Rea 6430 from your example.

    Could you show the calculation broken down further? or offer any other possible help.



  5. Matt Glover says:

    Sorted it! 🙂

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