A few years ago, I received a call from a contractor asking for help mitigating a situation with a governmental transport agency in regards to monitoring downhole pressures as they were drilling under a six-lane highway crossing. They were asked to provide details on the drilling fluid they were using and the expected annular pressure while drilling. In order to do this, one must look at the functions of the drilling fluids, the properties of the drilling fluids (like viscosity and solids content), the volume of fluids being pumped, and the rate or speed of drilling.
During the drilling process, a contractor circulates drilling fluids through the bore. The drilling fluids have several functions that keep the hole open and stable in order to pull the pipe through with ease. The primary functions of a drilling fluid are: