Drilling Fluids: Does It Matter Where Bentonite is Mined?

High-grade bentonite mined in Wyoming and Montana has a much higher swelling capacity than bentonites found elsewhere. *Source: Cetco Drilling Products*

Wyoming bentonite ground into a 200-mesh powder. *Source: Cetco Drilling Products*

Wyoming sodium bentonite chips withstand 50 psi in lab tests. *Source: Cetco Drilling Products*

Calcium bentonite from West Texas crumbles at 21 psi. *Source: Cetco Drilling Products*

Under a microscope, calcium bentonite, — Under a microscope, calcium bentonite shows its needle-like structure. The platelet structure of sodium bentonite, right, gives it superior swelling capacity. *Source: Cetco Drilling Products*

During my travels as a territory sales manager for CETCO, I often hear comments about the price of bentonite. Many companies offer bentonite-based products and they have many different price points. For example, bentonite chips used to seal and decommission boreholes are offered by many companies with a wide range of prices. Not all chips are created equal! Some are a high-grade Wyoming sodium bentonite and some are mined in other areas of the country. These chips do not have the swelling ability of the high-grade Wyoming sodium bentonite. This is due to the percent of sodium bentonite versus the lesser swelling calcium type. This inferior swelling capacity leads to the use of more chips to fill a space than would be necessary if high-grade Wyoming sodium bentonite is used. Therefore, the initial cheaper price ends up more costly in the end. Inadequate swelling translates to a poor seal, and can lead to migration of surface water and containments to our groundwater.

When comparing bentonite chips, another reason why it matters where bentonite is mined is structural integrity. In a laboratory test, we used a machine to measure the force it takes to push out of a cylinder the high-grade Wyoming sodium bentonite chips, and chips found in West Texas. We found that it took 21.18 psi to push the West Texas chips out of the cylinder, which is less than half of the high-grade Wyoming sodium bentonite chips, which took 50 psi.

As a professional in the drilling field, it is our responsibility to ensure we choose products that will help protect our precious groundwater resources. Inferior bentonite chips do show their face on the market; when something is far less expensive, there is usually a reason.

Another reason why it matters where bentonite is mined is the structure of the bentonite itself. High-grade Wyoming sodium bentonite (montmorillonite) has a platelet structure, while calcium bentonite (attapulgite) deposits found all over the world have a needle-like structure. Calcium bentonites do not have the swelling capacity found in Wyoming sodium bentonite. Due to the needle-like structure, calcium bentonite does not provide gel strength and fluid-loss control when used for drilling fluid. The formation of a neat and tight filter cake, which prevents fluid loss and inadvertent returns, will not occur, resulting in poor borehole stability.

The purest reserves of sodium bentonite are found in Wyoming and Montana. There are other areas where sodium bentonite is found, but those beds are not as pure and may contain other minerals such as gypsum. These other minerals will not help the drilling process!

In summary, when working in the vertical or horizontal drilling markets, ask your bentonite supplier where their bentonite is mined. If it is not Wyoming or Montana, you may not be buying the quality you expect. Don’t blame us: That is where God put it!