WorldWide Drilling Resource

29 MARCH 2021 WorldWide Drilling Resource® Bentonite: Tablets or Chips? Adapted from Information by CETCO Bentonite tablets, also known as bentonite pellets, are often misunderstood regarding structural integrity and placement, with many believing bentonite tablets are inferior to bentonite chips for sealing a well bore, maintaining structural integrity, and ease of placement. Because both bentonite chips and tablets are commonly used for well abandonment and sealing the space above the well screen area on water wells and environmental monitoring wells, a clear understanding may help to dispel these myths. Bentonite tablets are more costly because of the added processes required to manufacture them. Bentonite chips are made from stockpiled bentonite, allowed to field dry to a specific moisture, and then screened to the proper size; while bentonite tablets are made from a higher quality bentonite, first field dried to a specific moisture content, and then dried in a rotary kiln dryer. Afterward, the bentonite for tablets is screened to a granular consistency and compressed into uniformly-shaped tablets of different sizes. How does the manufactured composition figure into their overall usefulness and value? The first myth about tablets lacking structural integrity was tested for pressure resistance and penetration. As an experiment, both chips and tablets were hydrated separately in two-inch PVC pipes for a couple of hours. Then one-inch PVC pipe with caps on both ends was used to try to push out the hydrated bentonite. Using a laboratory press, measurements revealed 50 pounds per square inch of pressure was required to move the chips. Under the same conditions, 96.5 pounds per square inch of pressure was required to move the bentonite tablets. Next, a cone penetrometer, WTR Bentonite & Chips cont’d on page 32.