Eiffel Trading 101: Drilling Mud
Drilling mud, also called drilling fluid, is essential in many types of drilling (including oil and gas, explorational drilling, and water wells). Drilling mud comes in a few different varieties and serves multiple purposes to a drill string. Keep reading to learn more about its history, functions, and the most common types of drilling mud used today.
History of Drilling Mud
Drilling mud has an extensive history, documented as far back as 1845, when a French engineer named Pierre-Pascal Fauvelle used water circulation to assist in drilling a new well. He achieved 560ft in just 23 days (for comparison, a dry auger well ten years earlier reached 1,771ft in eight years).
The first documented use of a water-based mud is considered to have been in 1900 at Spindletop (Texas) – and literally involved mud. Engineers noticed that the water used for drilling was mixing with the clay and sand that had repeatedly been collapsing the well and filling it with debris. They tested mixing the freshwater with the clay, creating mud, and the results not only increased the stabilization of the well, but the increase in viscosity of the fluid provided enough strength to bring drill cuttings back to the surface of the borehole.
Drilling Mud Functions and Benefits
Drilling mud is pumped down the drill string to the bit, where it is pushed out of the pipe, then flushed back up the borehole to the surface. The mud carries clay and rock cuttings back to the surface, creating a clean space for the drill bit to continue working, and is collected back at the surface for cleaning and recirculation or discharge.
Drilling mud is essential to keeping a drill string’s drill bit clean, cool, and lubricated during drilling. When drilling is paused, or when the drill string is put into or removed from a borehole, drilling mud suspends drill cuttings to prevent damage to the bit or drill string. It also helps to prevents formation damage – drilling mud is combined with additives to ensure that the surrounding rock formation does not absorb the drilling fluid.
Types of Drilling Mud
There are several types of drilling mud available, but the three most common are listed below.
1. Water-Based
Water-based muds (WBMs) are used in around 80% of wells today. Because the base fluid is water, WBMs are typically the least expensive option. This drilling mud is a combination of water, clay, and chemicals. Clay is used to increase the viscosity of the drilling mud, which works to transport cuttings from the drill bit back to the surface.
WBMs can be either dispersed or non-dispersed. Non-dispersed WBMs are either natural or lightly-treated compositions that are best suited for shallow wells or top-hole drilling. By contrast, dispersed systems are treated with thinners or other chemicals which allow the drilling fluid to more easily break down clays and other materials in its path.
WBMs are commonly used in vertical wells, at shallow or medium depths.
2. Oil-Based Muds
Oil-based drilling muds (OBMs) are petroleum-based drill fluids. They address several issues that WBMs cannot – including contaminants and increased borehole temperatures. One advantage of using OBMs is that they create lower well friction, making it a stronger choice for long-reach wells.
OBMs are well-suited for directional drilling and drilling at greater depths.
3. Synthetic-Based Muds
Synthetic-based drilling muds (SBMs) are primarily used in offshore rigs. A major benefit of SBMs is that they exhibit many of the same qualities as OBMs, but aren’t included in some of the same regulations that cover offshore drilling. For instance, some regions prohibit discharging cuttings that have been drilled with OBMs, but not with synthetic systems. SBMs can be used for either horizontal or directional drilling.
Putting It Simply…
Drilling mud is pumped from a mud pit through the drill string, down and out of the nozzle located on the drill bit. The borehole takes in the drilling mud and churns out clay and rock cuttings to cleanse and stabilize the well. Drilling mud is as essential to oilfield drilling as fresh air is to humans.
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