When a driller ran a herd of cattle through a wet field in Spindletop, Texas to make mud back in 1901, then used the mud to lubricate a hot drill bit – history was made. Mud has been used in the oilfields ever since.
The mud utilized in today’s drilling process has changed as much the gas and oil industry, itself. Gone are the days when drilling fluid consisted of clay and water. What’s commonly referred to as “drilling mud” today isn’t mud at all, but an intricately-engineered mix of ingredients, including mineral oil, paraffins, bentonite, lime, synthetics, hydrocarbon-based materials and a host of other ingredients.
While the technology and chemistry of drilling mud have become much more complex, the concept has remained the same. Drilling fluids are essential to drilling success, both maximizing recovery and minimizing the amount of time it takes to achieve first oil.
Drilling fluids (or drilling muds) have several functions, including carrying bore cuttings to the surface and cooling and lubricating the drill “string.”
On a drilling rig, mud is pumped from the mud pits through the drill string where it sprays out of nozzles on the drill bit, cleaning and cooling the drill bit in the process. Ray Nardo, who works on a rig in the Utica shale basin, said the mud then carries the rock cuttings up the casing, where it rises back to the surface. “The cuttings are then filtered out with a shale shaker and the mud returns to the mud pits where the drilled “fines” settle to the bottom,” explained Nardo. The pits are also where the fluid is treated by adding chemicals and other substances.
Drilling deeper, longer and more challenging wells requires more efficient and effective drilling fluids.
Drilling fluids also help to control pressure in a well by offsetting the pressure of the hydrocarbons and the rock formations. Weighing agents are added to the drilling fluids to increase its density and, therefore, its pressure on the walls of the well.
Another important function of drilling fluids is rock stabilization. Special additives are used to ensure that the drilling fluid is not absorbed by the rock formation in the well and that the pores of the rock formation are not clogged.
The longer the well, the more drill pipe is needed to drill the well. This amount of drill pipe gets heavy, and the drilling fluid adds buoyancy, reducing stress. Additionally, drilling fluid helps to reduce friction with the rock formation, reducing heat. This lubrication and cooling helps to prolong the life of the drillbit.
All Mud Is Not Created Equal
The three main categories of drilling fluids are water-based muds (which can be dispersed and non-dispersed), non-aqueous muds, usually called oil-based mud, and gaseous drilling fluid, in which a wide range of gasses can be used.
This where the drilling fluid engineer comes in. The drilling engineer oversees the drilling, adding drilling fluid additives throughout the process to achieve more buoyancy or minimize friction, whatever the need may be.
In addition to considering the chemical composition and properties of the well, a drilling fluid engineer must also take environmental impact into account when prescribing the type of drilling fluid necessary in a well. Oil-based drilling fluids may work better with a saltier rock. Water-based drilling fluids are generally considered to affect the environment less during offshore drilling.
Disposal of drilling fluids after they are used can also be a challenge. Recent technological advances have established methods for recycling drilling fluids.
The returning mud can contain natural gasses or other flammable materials which will collect in and around the shale shaker/conveyor area or in other work areas. Because of the risk of a fire or an explosion if they ignite, special monitoring sensors and explosion-proof certified equipment are commonly installed, and workers are advised to take safety precautions. The mud is then pumped back down the hole and further re-circulated. After testing, the mud is treated periodically in the mud pits to ensure properties which optimize and improve drilling efficiency, borehole stability, and other requirements listed below.
The Business of Mud
Nardo said that there are numerous companies nationwide that specialize in the production of drilling fluids.
“It’s a competitive business, these days,” said Nardo. “Think of it this way: drilling mud is needed when anything drilling is going on. There’s a demand for it. It’s a science.”
Nardo said the companies are usually regionally focused and seek to provide the safest drilling fluids at the lowest possible cost.