Bit Hydraulics And Optimization- Surface Horsepower
In order to maximize a hydraulics program, all aspects concerning drilling fluids and the associated equipment must be considered. The first component in any hydraulic design is the surface equipment and the hydraulic horsepower available from them. There are two limiting factors on the surface hydraulic horsepower.
The first is the flow rate range. As discussed earlier, the flow pattern in the annulus should be laminar, therefore the upper limit for the flow rate is a Reynolds Number of 2000. The highest velocity in the annulus will be around the collars, and this velocity can be determined by calculating the “critical velocity” over that section. In addition, running the pumps at that upper range is not always advisable because there will be more wear and tear on the pumps and much more fuel consumption.
The lower limit is a range where there is sufficient hole cleaning. This is determined by using the velocity around the drillpipe and the largest annular section (normally the upper hole section or drillpipe/riser section).
A normal range is around 50 ft/min.
The second factor is the operating pressure of the mud pumps. Most mud pumps can produce the required pressure with little problem. However, because of the various components associated with the surface system (standpipe, rotary hose, pulsation dampener, etc.) the maximum surface pressure is usually limited to some value less than the maximum rated pump pressure.
The available “surface horsepower” is then determined by:
where: Hps = Surface Horsepower
P = Pump Pressure (psi)
Q = Pump Flow Rate (gal/min)
Once the surface horsepower has been determined, the horsepower distributions can be made:
where: Hpc = Circulation Horsepower
Hpb = Bit Horsepower
