STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Mud Hydraulics 835
words, the total pressure drop between two points of a flow conduit is the sum
of the components mentioned above. Thus,
AP = AP) + AP4 + AP, (4- 104)
where APF = frictional pressure drop
APa = accelerational pressure drop
AP, = gravitational pressure drop (hydrostatic head)
Equation 4-104 expresses the principle of additive pressures. In addition to
Equation 4-104, there is the equation of state for the drilling fluid.
Typically, water based muds are considered to be incompressible or slightly
compressible. For the flow in drill pipe or drill collars, the acceleration
component (AP,) of the total pressure drop is negligible, and Equation 4-104
can be reduced to
AP = APk + APc, (4-1 05)
Equations 4-102 through 4-105 are valid in any consistent system of units.
Example
The following data are given:
Pressure drop inside the drill string = 600 psi
Pressure drop in annular space = 200 psi
Pressure drop through the bit nozzle = 600 psi
Hole depth = 10,000 ft
Mud density = 10 lb/gal
Calculate
bottomhole pressure
pressure inside the string at the bit level (above the nozzles)
drill pipe pressure
Because the fluid flow in annular space is upward, the total bottom hole
pressure is equal to the hydrostatic head plus the pressure loss in the annulus.
Bottom hole pressure Photlom (psi),
Ph