This is the pressure created (or needed) to move drilling fluid through pipe. In oil field terms, it is the pressure generated by the mud pump in order to move the drilling fluid from the mud pump around the system and back to the flowline. In this section, the terms Pump Pressure and Hydraulic
Pressure will be used interchangeably. This type of pressure can be calculated at any point in the circulating system.
Pressure drop or pressure loss is the amount of pressure needed to move the fluid over a given distance, for example,
the hydraulic pressure (pump pressure) remaining at point B in the figure is 600 psi. However, the system pressure loss at point B is 300 psi. That is, 300 psi is needed to pump the mud from point A to point B.
The hydraulic pressure (pump pressure) remaining at point E in the figure is 225 psi. However, the system pressure loss at point E is 675 psi. That is, 675 psi is required to move the mud from point A to point E. (300 psi from A to B and 375 psi from B to E.)
The total system pressure loss in the drawing (A to F) is 900 psi.
Note: The pressure at any given point in the circulating system is the sum of the hydrostatic, hydraulic, and imposed pressures which exist at that point.
Typically, hydraulic pressures will be calculated in order to:
• Determine the total pressure being exerted at the casing shoe (generally the weakest point in the circulating system); the bottom of the hole; or any other point (such as a lost circulation zone). After
this pressure is determined, it is often converted into a mud density equivalent and reported as the E.C.D. (Equivalent Circulating Density) for that depth.
• Determine the anticipated pump pressure, using:
- mud properties
- drill string configuration
- bit size
- total flow area for the bit
- flow rate
• Determine the nozzle size for a bit, using:
- maximum pump pressure allowed
- mud properties
- drill string configuration
- bit size
- flow rate
