Calculate jet velocity through bit nozzles for drilling hydraulics optimization and hole cleaning analysis.
Nozzle velocity (jet velocity) is the speed of drilling fluid as it exits the bit nozzles. It controls how much hydraulic energy reaches the bottom of the hole to clean the bit and remove cuttings from the bit face. For a given flow rate, smaller total nozzle area produces higher jet velocity and stronger impact on the bottom.
In most bit hydraulics programs, nozzle velocity is evaluated alongside bit pressure drop, hydraulic horsepower at the bit, and annular velocity. Typical design targets often keep nozzle velocity above about 250 ft/s for effective bottom-hole cleaning, while avoiding unnecessarily high values that drive excessive pressure losses and equipment loading.
This calculator uses standard field-unit relationships between flow rate in gallons per minute (gpm), total nozzle area in square inches (in²), and jet velocity in feet per second (ft/s). It lets you see how changes in flow rate or nozzle sizes affect jet velocity without touching the underlying well hydraulics model.
The starting point is the continuity relationship between flow rate, area, and velocity:
Q = A × V
Where Q is volumetric flow rate, A is total flow area, and V is average jet velocity.
When Q is entered in gpm and total bit nozzle area A in in², this relationship can be written in field units as:
V = 0.5362 × Q / A
V = nozzle velocity (ft/s), Q = flow rate (gpm), A = total bit nozzle area (in²). The constant 0.5362 converts between gpm, in², and ft/s.
Total nozzle area is the sum of the individual nozzle areas:
Atotal = Σ Ai = Σ (0.000767 × Ji²)
Where Ji is each nozzle size in 32nds of an inch (e.g. a "13" jet is 13/32 in). The constant 0.000767 converts nozzle size in 32nds into area in in².
Key variables:
Consider a bit with three 13/32-in. nozzles and a circulation rate of 400 gpm. First calculate the total nozzle area:
Atotal = 0.000767 × (13² + 13² + 13²)
Atotal ≈ 0.3889 in²
Then apply the nozzle velocity formula:
V = 0.5362 × Q / A
V ≈ 0.5362 × 400 / 0.3889 ≈ 552 ft/s
In this example, the jet velocity is on the order of 500–550 ft/s, which is typical for many hydraulics optimization programs that aim for strong bottom-hole cleaning while avoiding extreme nozzle velocities that drive excessive pressure loss.
V = 0.5362 × Q / A
This formula is derived from the Halliburton Red Book nozzle velocity equation expressed in ft/min, converted to ft/s:
Vft/min = 32.17 × Q / A
Vft/s = Vft/min / 60
A = n × π × (d/2)²
Total flow area for multiple nozzles
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