Portable Mud Tester

As oil wells are drilled, drilling fluid, also referred to as mud, is pumped down the pipe to cool and lubricate the drill bit, bring rock cuttings to the surface, and stabilize the rock formations being drilled. Portable mud testers, like this early example from 1965, are used in the field to periodically check the chemical composition of the drilling fluid and ensure it’s doing its job correctly.

Mud engineers create a "mud program" prior to drilling, establishing which ingredients should be used in the drilling fluid, the concentrations of each ingredient, and if that composition should change as the well is drilled through new and different geological layers. They are also responsible for monitoring the composition of the mud in the field to make adjustments as needed.

The formula for mud is specific to each well and can vary at different depths to make sure they do not damage the formations they are meant to protect. The density of the mud creates pressure within the well, stabilizing the well wall. This ensures that liquids within the formations, like water, don’t pour into the well and that formations don’t crack during the drilling process.

In addition to non-toxic ingredients like water, calcium carbonate, and clay, muds can contain potentially toxic chemicals like hydrochloric acid, barite, anhydrous lime, and crude oil. The specific formula created for each well ensures that these potentially harmful chemicals and hydrocarbons fall within regulated levels.