API grade bentonite is bentonite that meets API Specification 13A, the American Petroleum Institute's standard for drilling fluid materials. Oil and gas drillers use it as the base of water-based drilling mud, where it builds viscosity, carries cuttings and seals the borehole wall.
The grade is defined by performance tests on a standard mud made from the clay. A seller's claim of API grade means little until you see those results for the lot you are buying.
What the specification tests
For the main bentonite section of API 13A, a suspension of the clay is mixed with water to a set recipe, aged, and tested on a viscometer and a filter press. Product data sheets and published references commonly cite these limits:
- The viscometer dial reading at 600 rpm must be at least 30.
- The yield point must not exceed three times the plastic viscosity.
- The filtrate volume must not exceed 15 mL.
- The residue retained on a 75 micron sieve must not exceed 4% by mass.
Check the edition
API revises its standards, so confirm every limit and test method against the current edition you contract to. Name that edition in your purchase order.
Other grades in the same standard
API 13A also covers OCMA grade bentonite and non-treated bentonite, each with its own requirements. OCMA grade has lower performance limits and suits less demanding wells. Non-treated bentonite must meet its limits without added polymers or other additives.
Buyers sometimes receive a polymer-treated clay labelled as API grade. Polymers can raise viscosity on the day of testing but break down with heat and time downhole. If your well programme needs untreated clay, say so in the specification.
Indian supply and activation
Most Indian bentonite is calcium or mixed bentonite. Reaching API limits usually needs careful selection of the raw clay and soda activation, explained in activated bentonite. Some units can meet the standard consistently. Others pass on a selected sample but drift on production lots.
Some buyers also ask whether the plant holds an API Monogram licence for Spec 13A. API grants this to manufacturers it has audited. You can check a licence on API's public directory, and it is worth checking before you rely on a certificate that shows the monogram.
How to buy it
- Name API 13A, the edition and the section in your purchase order.
- Ask for test results from recent production lots, not just one sample.
- Have samples drawn from the packed lot at loading and tested by an independent laboratory that runs API test methods.
- Keep a sealed retention sample from each lot in case of a later dispute.
Next step
We audit processing plants, check samples and documents, and have lots tested before they ship. Read what tests belong on a bentonite COA for the full list. To source drilling grade clay, book a free sourcing review.