There is no Grade A bentonite.
Bentonite has no single quality ladder. There are industry standards, and a grade simply means the clay meets one industry’s specification. API and OCMA are two of those, and both belong to drilling.
What API and OCMA actually are
American Petroleum Institute
The document is API Specification 13A, “Drilling Fluids Materials”. It covers everything that goes into drilling mud: barite, bentonite, attapulgite, sepiolite, starch and more. Bentonite is tested on a suspension of 22.5 g in 350 cm³ of water, by the methods in API 13B-1.
ISO 13500 is the international equivalent and follows API 13A closely.
Oil Companies Materials Association
A British body that wrote materials specifications for the North Sea oil industry. Its bentonite specification was designated DFCP-4.
OCMA no longer exists, but its specification lives on inside API 13A as OCMA-grade bentonite: Section 19 in the current 19th edition, Section 11 in earlier editions.
A buyer asking for “OCMA grade” today is asking for the OCMA-grade section of API 13A.
Section 9 against OCMA-grade
The two bentonite specifications most export buyers ask for, side by side. Read it carefully: one is not simply better than the other.
| Property | Test method | Section 9 Bentonite | OCMA-grade bentonite |
|---|---|---|---|
| Viscometer dial reading at 600 r/min | API 13B-1 | min 30 | min 30 |
| Yield point / plastic viscosity ratio | API 13B-1 | max 3 | max 6 |
| Filtrate volume, 30 min | API 13B-1 | max 15.0 cm³ | max 16.0 cm³ |
| Residue greater than 75 µm | Wet sieve | max 4.0% | max 2.5% |
| Moisture | Oven dry | max 10% | not specified |
Who asks for it
Oilfield mud companies that want the most viscosity per tonne and specify by the API section number.
Who asks for it
Water-well, HDD and many Gulf and African drilling buyers. The most traded drilling bentonite grade out of India.
Where our drilling lots sit against those limits
Our two drilling lots, OCM and DRL, are specified against these two columns. See the drilling grade specification.
“API grade” and the API Monogram are different things
Anyone can write “API grade” on a bag. Only a licensee may print the API Monogram, and that licence needs an API Spec Q1 quality system and an on-site audit by API.
We supply to the API 13A specification with an independent certificate of analysis for every shipment. We do not hold the Monogram, and we do not print it.
What backs each claim
| Claim | What backs it |
|---|---|
| “API grade”, no certificate | The seller’s word |
| Certificate from an independent accredited lab | An independent test |
| Pre-shipment inspection (SGS, BV, Intertek) | A witnessed sample |
| API Monogram | An audited system |
How bentonite is classified
Every industry, and the standard that governs it
| Application | Governing standard | The numbers that decide it |
|---|---|---|
| Drilling fluids | API Spec 13A (Section 9, OCMA-grade) ISO 13500 | 600 r/min dial reading, YP/PV ratio, filtrate, residue |
| Piling, diaphragm walls, tunnelling | EN 1538, EN 1536 Project specification | Density, Marsh funnel viscosity, fluid loss, pH, sand content |
| Foundry green sand | AFS test methods IS 12446 | Green and dry compression strength, active clay, fineness |
| Iron ore pelletising | No standard | Swell index, Enslin water absorption, methylene blue index |
| Geosynthetic clay liners | ASTM D5890, ASTM D5891 | Swell index and fluid loss |
| Cat litter | No standard | Clump strength, absorption, dust |
| Ceramic bodies | No standard | Plasticity, dry strength, fired colour, shrinkage |
Two mistakes that cost buyers money
Buying “Grade A”
Grade A, Grade 1, Premium and Super are seller labels with no meaning outside that seller’s office. Ask for the standard, or the test method and the value: “swell index 24 mL/2 g by ASTM D5890”.
Buying one number instead of a range
A single good result shows one good lot. A published guaranteed range, with a certificate for every shipment, shows a supplier willing to be held to it.
Test it against what you buy today.
A 2.5 kg sample with its certificate of analysis, sent by DHL or FedEx. Tell us your current supplier's figures and we will tell you honestly how ours compare.