The system with downhole tools means the drill string consisting of drill pipe, drill collar, down hole equipment (MWD, PWD, LWD) and a bit. The process of optimization this system is more complicated than the simple system. Due to the fact that the down hole equipment responses differently when changing in flow rate, even the similar tool, the pressure responses cannot be modeled with simple equation.
There are two methods used to optimize drilling hydraulics with downhole tools.
1. The first method is to subtract the expected pressure loss generated by downhole tools from the surface pressure. After you get the reduced surface pressure, you optimize the system with lower pump pressure.
2. The second method is to optimize whole system as if there is no downhole equipment and then you subtract the expected pressure loss by downhole tools from available bit pressure.
What are the differences between both methods of optimization with downhole tools?
The first method has a draw back because the predicted pressure loss across the tool has more uncertainty than the second method because the flow rate is not determined at the beginning.
The second gives a higher flow rate and larger nozzle areas because you optimize the large pressure at the beginning. The higher flow rate has better capability to remove butting in the annulus than the lower flow rate. What’s more, the bigger nozzle areas give more flexibility to configure nozzles. Another advantage is in comparison to the first way is that the flow rate is known therefore you will have good downhole pressure loss prediction.
Note: for the detailed calculation, it will be fully described after we discuss about the equations used in drilling hydraulics. Please keep continue reading our drilling formula blog.
Reference: Drilling Hydraulic Books