Drilling mud or drilling fluid is an important component of almost any drilling operation.
Mud is mixed in special surface pits and then pumped through the drilling string into the well. After exiting through the nozzles on a drilling bit, mud returns back to the surface through the annulus between the drill string and wellbore.
At the surface, rock cuttings are removed from the mud and it is pumped back into the well.
What Is the Purpose Of Drilling Mud?
Lubricating the wellbore – mud helps to decrease the friction between the wellbore and a drilling string. This means more force can be transferred to the bit.
Lifting drilling cuttings to the surface – the rock cuttings need to be removed from the well for efficient drilling and to avoid stuck-in-hole situations.
Drilling mud has a higher viscosity than water and it allows cuttings to travel easier to the surface. Mud also allows to suspend these cuttings in the well and prevent it from settling on the top of the bit or in the heel when circulation is stopped.
The cuttings coming from the wellbore to the surface are often used by mud loggers and geologists to get a better understanding of the downhole conditions.
Cooling the drilling string and the drill bit – this helps the drilling bit to last longer in the well. Replacing a drilling bit takes time and can increase the cost of the operation.
Pressure control – hydrostatic pressure of the mud helps to avoid the well kicks. However, using mud with very high density can result in lost circulation and that’s why it is important to adjust mud composition based on the wellbore conditions.
Transmit signal – tools such as MWD and LWD rely on mud to send signals to the surface.
Ads buoyancy – this helps to decrease the weight of the drilling string which means less force is required at the surface to pull it up.
Stabilizing formation – some formations can be affected by water and using drilling mud with special chemicals can help to prevent this.
Related: What is Mud Logging in Oil and Gas?
What Is Drilling Mud Made Of?
The simplest drilling fluid is just water however in almost every drilling operation additional chemicals are added to improve its performance.
There are two main types of drilling mud, water-based and oil-based. There are also air-based drilling muds that use nitrogen or similar gas to create foam which is pumped downhole but these muds are not as common.
Water-based mud is made up of water and special chemicals are added to increase its viscosity, density and to prevent formation damage. This is the most common type of mud used in the oil and gas industry.
Common minerals added to mud are bentonite, gypsum and barite.
Oil-based muds are used when there is a high chance of formation damage or in swelling formations.
The disadvantages of oil-based muds are higher costs, challenges with disposing of them and contamination of rock samples coming to the surface.
Common substances used in oil-based muds are mineral oil, diesel and kerosene.
What Is A Drilling Fluids Engineer?
A drilling fluid engineer or mud engineer is the guy that takes care of mud preparation and is responsible for adjusting mud composition as well is being drilled.
Usually, mud engineers have a background in chemical engineering but some just have a high school diploma and a lot of field experience from either working on drilling or service rigs.
Read next: Working on a Drilling Rig: Positions and Responsibilities