What Is Drilling Mud?

Drilling mud, also called drilling fluid, aids in the process of drilling a borehole into the earth. Such holes are drilled for oil and gas extraction, core sampling, and other purposes.

Key Takeaways

  • Drilling mud is used during the oil and gas extraction method and helps in the process of drilling a borehole into the earth.
  • Drilling mud is used to lubricate the drill bit and transport drill cuttings to the surface.
  • Drilling mud is regulated on a statewide basis and is exempt from federal regulations because it is classified as special waste by the U.S. EPA.
  • It is important to dispose of drilling waste in a safe manner because it can contaminate soil and groundwater.
  • There are three main types of drilling mud: water-based, oil-based and synthetic-based.

Understanding Drilling Mud

Drilling mud is used to lubricate the drill bit and transport drill cuttings to the surface. Drill cuttings are broken bits of solid material that are produced as the drill bit breaks the rock. As it circulates up from the drill bit, the drilling mud carries drill cuttings up to the surface, where the mud and the cuttings are separated.

Drilling muds have been used to improve drilling operations for much of modern history. Water was used to soften surface material and to remove clippings when groundwater wells were drilled. Contemporary drilling operations are more sophisticated and wells can reach miles below the surface in order to access oil and natural gas deposits.

There are now are three main types of drilling mud: water-based, oil-based, and synthetic-based. The synthetic-based muds are more frequently used because they have less environmental impact and are quicker to biodegrade than water- and oil-based fluids.

Drilling Mud Disposal

Throughout the drilling process, drilling mud is recirculated, which helps decrease waste by reusing as much mud as possible. When the drilling process is finished, the drilling waste must be disposed of in some way. The U.S. Environmental Protection Agency classifies drilling muds as special waste, meaning that they are exempt from many federal regulations. As a result, laws concerning the disposal of drilling muds vary by state.

California, for example, has some strict regulations regarding drilling mud. Pit burial is a very common technique, in which the waste is placed in a manmade or natural excavation. However, burial is not a good method for waste that contains high concentrations of oil and industrial chemicals. The waste can easily contaminate soil and groundwater when the hydrocarbons and other chemicals leach into the earth, and polluted groundwater can take years or even decades to dissipate and often spreads to other areas. Most water-based muds are simply disposed of after the drilling job is completed, but many oil- and synthetic-based muds can be recycled.

Drill cuttings can also be recycled and reused after the hydrocarbons are removed. Recovering drill cuttings and drilling muds is often practical and cost-effective and is an environmentally sustainable process. The most efficient and successful way to remove volatile contaminants from muds and cuttings is thermal desorption. Indirect rotary kilns are ideal for recovering drill cuttings and drilling muds.