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Drilling specialist explains bentonite properties

Schlumberger – MI SWACO Drilling Fluid Specialist Andrew Bilton has discussed the common industry misconception that all bentonite is the same.

The reaction of bentonite when mixed with water is what makes it an effective component of a drilling fluid, earning it the title of “miracle mud” throughout the industry.

However, in an article published on LinkedIn, Mr Bilton said bentonites are classified into several types – such as calcium, sodium and potassium – although sodium bentonite it the most common choice in the drilling industry.

“While they are composed of the same fundamental building blocks, calcium bentonite does not exhibit the same desirable properties as its sodium cousin,” said Mr Bilton.

“These major differences in swelling, suspension and thixotropy can affect your drilling fluid (mud) and the ‘functions of the drilling fluid’ which in turn can have a significant impact on and the overall success and profitability of your project.

“Untreated calcium bentonite is not suitable for drilling fluid, so it is typically treated (beneficiated) during the milling process by adding sodium carbonate (soda ash), long-chain synthetic polymers, carboxymethylcellulose (CMC), starch or polyphosphates.”

Contrarily, Mr Bilton explains the structure and chemical composition of sodium bentonite means when the clay is mixed in water, the dry stacks of platelets begin to hydrate and swell as the water is attracted to both the negative clay surface and the positively charged ions in between the layers.

“As the individual platelets separate (disperse) in the water, their surface area and colloidal activity increases producing a viscous fluid that can suspend solids and seal up the bore/well bore,” said Mr Bilton.

“Sodium bentonite swells through a process of osmotic and crystalline swelling providing a 20-fold increase in volume. Calcium bentonite on the other hand undergoes crystalline swelling only resulting in a 2-fold increase in volume.

“Better swelling (hydration) means increased surface area and colloidal activity which translates into improve viscosity, better suspension capability, superior gel strengths, greater filtration control and higher yield.”

Mr Bilton said an intelligently designed and maintained drilling fluid is a critical component of a drilling operation and a good bentonite is often a critical component of that drilling fluid.

“When you consider all the functions of a drilling fluid, and how those functions impact the success or failure of the drilling operation, sodium bentonite outperforms all other products on the market.”

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