Mud Flashcards
What is the most important characteristic of mud?
Mud weight. Determines ability to control the well with hydrostatic pressure.
What are the key functions of mud? What is one thing it should not do.
Well control (hydrostatic pressure)
Cooling
Clean the bit (via the nozzles)
Cleans cuttings from the drill face
Stabilizing the bore hole (pressure)
Lifting the cutting / enabling cutting samples for analysis
Telemetry / communications
Jet drilling
drive force for the turbine drill bit
IT SHOULD NOT BE DAMAGING… Ie it should not be composed in such a way that it goes into the rock and reduces permeability, thereby reducing production capability of the well.
Absorb contaminatins and temperature flexible- else risk solidification. Lubrication (ie oil based mud)
How much does shell spend on mud?
Approx $800mln pa 3rd largest component of wells spend
What is the main reason for acidizing a well?
Prior to completion there may be the need to acidize the well to remove the coatings on the rock used by the drilling mud.
If for example you’ve drilled with polymer (for viscosity) and limestone (for weight) in a horizontal section that would need to be removed for the rock to produce.
What type of mud are you likely to need to drill through clay?
OBM oil based mud. It avoids the clay being absorbed into the mud and thickening it to a point of being un pumpable. Often it is rented from a supplier and then taken away and reconditioned.
Two potential risks of using oil based mud OBM?
- When drilling through a gas reservoir you may absorb gas into your mud which can inhibit well control / well safety
- In an exploration rather than production well, oil based mud can risk “dirtying” the data being collected as a present hydrocarbon
If your cuttings flow rate drops significantly below your mud flow rate, what might cause this and how can you mitigate? What should you not do?
- The hole may have some blockage or be washed out and then the downforce from the washed out debris offsets the mud flow rate
- To mitigate you can increase the mud viscosity so that it better collects the cuttings and cleans the well. You can also increase glow rate.
- Don’t increase density it may fracture your rock / damage the well
Why would you take samples of well / rock water?
To check for mud compatibility. The mud contains water and chemicals which could react with the water in the well and cause a precipitation / chemical reaction that could destroy the reservoir permeability.
What is pobm
Pseudo oil based mud
What is breaking circulation?
After you’ve pulled out if hole and stopped pumping the mud settles and polymers / clays make it more viscous. When you need to start repumping it takes some time to return to fully fluid state, requires slow progressive start up of the pumps etc. this process is referred to as breaking circulation.
