What dose drilling fluid depend on?

1- Formation type 

2- Bottom hole pressure

3- Bottom hole temperature

4- Bit size or Hole size

5- Also through layers of the well determine the amount of fluid viscosity and weight

Drilling Fluids depend on:

1- Formation type 

2- Bottom hole pressure

3- Bottom hole temperature

4- Bit size or Hole size

5- How much the  trip margin?

6- Well location & Waste management  

7- Also depend up on if the section will be drilled reservoir or not.

8-  Local regulations  will be in mind also when choosing the drilling fluid for the Section will be drilled.

Up on all mentioned above you will be able to choose the suitable drilling fluid type with the right properties required to drill the well.  

1.Formation type and mass

2.Bottom hole pressure, temprature

3.Hole size, depth

4.Bit size