Drilling hydraulics affect directly drilling performance and this topic will focus on the basic principle of the drilling hydraulics.
Circulation System on Drilling Rigs
Typically, the rig circulation system is composed of mud pumps which deliver drilling mud from mud pits to hoses and pipes down to the bottom of the hole. Drilling mud is moved through a bit into the annulus and is finally returned back to solid control equipment and the mud pits (you can see from the following diagram).
Frictional Pressure Loss
Frictional Pressure Loss is pressure loss created when drilling mud flows through a flow path. Frictional pressure loss affects on pump pressure because higher frictional pressure loss, higher pump pressure is required to maintain the pump rate.
The following parameters affecting frictional pressure loss are as follows:
• Inner diameter of drill pipe, drill collar and heavy weight drill pipe
• Down hole tool as a mud motor, a rotary steerible tool, a MWD/LWD, etc
• Length of drill pipe, drill collar and heavy weight drill pipe
• Drilling fluid properties – mud weight, mud rheology (PV/YP)
• Hole size
• Length of the well
• Inner diameter of the previous casing string
• Flow area of the bit
• Flow rate
For more understanding, the diagram below demonstrates the frictional pressure loss during drilling operation.
Advantages of drilling hydraulics
• Optimize drilling performance (ROP)
• Improve hole cleaning
• Stabilize the wellbore
• Cool and lubricate drilling bits
• Transmit information from down hole tools (MWD/LWD)
• Provide wellbore stability
• Provide additional pressure besides hydrostatic pressure called equivalent circulating density (ECD)
Reference: Drilling Hydraulic Books