We’ve learned several calculations regarding pressure loss in the drilling system and today, we will combine all knowledge together so we will get the total pressure loss in the system excluding the bit.
Without downhole tool, the total pressure loss without bit is equal to summation of pressure loss at the surface equipment, pressure loss through drill string (drillpipe and drill collar) and pressure loss in the annulus.
The equation below demonstrates the system pressure loss excluding the bit:
Po = the system pressure loss excluding the bit
Cse = coefficient of surface equipment
Lp = length of drill pipe
Cpa = coefficient for annulus of the drill pipe
Cpb = coefficient through bore of drill pipe and tool joint
Lc = length of drill collar
Cca = coefficient for annulus of the drill collar
Ccb = coefficient through bore of drill collar
W = mud weight, ppg
PV = plastic viscosity of drilling mud, centipoise
Vf = viscosity correction factor
Q = flow rate, gpm
In the next topic, we will apply this concept to determine the optimum flow rate for the basic system.
Reference: Drilling Hydraulic Books