About API 13A Section 11 OCMA-Grade Bentonite
OCMA-grade bentonite is the drilling clay covered by API 13A Section 11. The name comes from the specification originally issued by the Oil Companies Materials Association, which API later brought into its own standard. Operators, tenders and mud programmes in several regions still call for OCMA bentonite by name, and it remains in regular use in water-based drilling fluids.
Section 11 balances its limits differently from Section 9. The 600 r/min dial reading must still be 30 or higher, but the yield point to plastic viscosity ratio may rise to 6 and filtrate to 16.0 cm³. In return, residue retained on a 75 µm sieve must not exceed 2.5 % by mass, a stricter fineness requirement than the 4.0 % allowed under Section 9. The outcome is a fine, fast-dispersing clay with a higher permitted yield point relative to its plastic viscosity.
We grind and classify our OCMA grade to meet the residue limit consistently, and test each batch in our NABL-accredited laboratory using API 13A procedures. Dial reading, YP/PV ratio, filtrate and residue are all reported on the batch Certificate of Analysis. When ordering, confirm the applicable edition of API 13A and whether your programme names Section 9 or Section 11, so the right grade and documents are supplied.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| Viscometer dial reading at 600 r/min | ≥ 30 (API 13A requirement) | API 13A, Section 11 |
| Yield point / plastic viscosity ratio | ≤ 6 (API 13A requirement) | API 13A, Section 11 |
| Filtrate volume | ≤ 16.0 cm³ (API 13A requirement) | API 13A, Section 11 |
| Residue > 75 µm | ≤ 2.5 % by mass (API 13A requirement) | API 13A, Section 11 |
| Moisture | ≤ 12 % (typical) | Internal method |
| Form | Fine, free-flowing powder | Visual |
| Colour | Cream to grey | Visual |
API 13A requirements are the Section 11 limits each batch is tested against; the applicable API 13A edition should be confirmed at order. Other values are typical, for guidance only. Guaranteed limits are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
Section 11 compliance testing
Dial reading, YP/PV ratio, filtrate and coarse residue are measured on every lot to API 13A Section 11 procedures, so OCMA-specified contracts can be verified directly from the Certificate of Analysis.
Fine grind, low residue
Residue above 75 µm is held at or below 2.5 %, which means fewer coarse particles reporting to shaker screens and desanders and quicker, more even dispersion through the mixing hopper.
Viscosity with carrying capacity
The 600 r/min minimum of 30 sets a solid viscosity base, while the wider YP/PV allowance of up to 6 suits programmes that prioritise yield point and cuttings-carrying capacity in top-hole sections.
Fluid-loss control
Filtrate of 16.0 cm³ or less in the standard API test gives a workable wall cake for spud and surface sections, and can be tightened further with fluid-loss additives where the programme requires.
Matches OCMA-specified tenders
Where a contract, tender or legacy mud programme names OCMA bentonite, this grade lets procurement match the specification exactly rather than seeking approval to substitute a different section.
Applications
OCMA-specified drilling programmes
Supplied to drilling contractors and mud companies whose operator specifications, tenders or historical programmes call for OCMA-grade or API 13A Section 11 bentonite in water-based systems.
Spud and surface-hole fluids
Used to build viscosity and gel strength in freshwater spud muds, where high yield point helps lift large cuttings from wide-diameter surface holes before casing is set.
Mining, water-well and foundation drilling
A fine-ground bentonite for rotary drilling of water wells, mineral exploration holes and large-diameter foundation bores, where fast mixing and low grit content help on site.
Usage & handling
- Start trials at around 25–60 kg/m³ in fresh water and adjust to the funnel viscosity and gel strength your programme specifies.
- The fine grind disperses quickly, but give the clay time to pre-hydrate before it meets brine, lime or cement contamination.
- Treat hard make-up water with soda ash to precipitate calcium, which otherwise lowers bentonite yield.
- Keep stock under cover and off the ground; damp bags cake and slow down mixing at the hopper.
Packaging & supply
- 25 kg and 50 kg HDPE or paper bags
- 1 MT and 1.2 MT jumbo (FIBC) bags for bulk mixing
- Custom or private-label packaging on request
- Batch CoA with API 13A Section 11 results, plus MSDS and TDS
Frequently asked questions
What does OCMA mean in OCMA bentonite?
OCMA stands for the Oil Companies Materials Association, which issued an early specification for drilling-fluid bentonite. API later incorporated that specification into API 13A, where it now appears as Section 11, OCMA-grade bentonite. Buyers still use the OCMA name in tenders and purchase orders. When you order, we supply it tested to the API 13A Section 11 requirements.
What are the API 13A Section 11 requirements?
API 13A Section 11 requires a viscometer dial reading at 600 r/min of at least 30, a yield point to plastic viscosity ratio of 6 or less, filtrate volume of 16.0 cm³ or less, and residue above 75 µm of no more than 2.5 % by mass. Each batch of our OCMA grade is tested against these limits. Confirm the applicable edition of API 13A at order.
Should I buy Section 9 or Section 11 bentonite?
Follow your mud programme, operator specification or tender. If it names OCMA grade or Section 11, buy this grade. If it asks for API bentonite or Section 9, choose our Section 9 grade, which has tighter YP/PV and filtrate limits. If you are free to choose, compare samples of both in your own laboratory under your water and mixing conditions.
Why is the residue limit tighter for OCMA-grade bentonite?
Section 11 allows a higher YP/PV ratio and filtrate than Section 9, but it compensates with a stricter limit of 2.5 % on residue above 75 µm. A finer grind means less abrasive grit in the fluid and faster dispersion during mixing. We control this through milling and air classification and confirm the result on every Certificate of Analysis.
Can I get an OCMA bentonite sample for laboratory testing?
Yes. Samples of OCMA-grade bentonite are available on request, together with the Technical Data Sheet. Many buyers run the API 13A Section 11 tests in their own or a third-party laboratory before approving a new source. Tell us the quantity you need for testing and the edition of API 13A you work to, and we will arrange the sample.