API 13A Bentonite Specifications

What API 13A bentonite evaluation measures

API Specification 13A establishes standardized requirements and test methods for several drilling-fluid materials, including drilling-grade bentonite. Evaluation is based on the performance of a controlled bentonite suspension rather than mineral composition or appearance alone.

A meaningful evaluation therefore cannot be based only on swelling, montmorillonite claims or a single viscosity value.

R600

R600 is the direct viscometer dial reading at 600 r/min. For API-oriented drilling-grade bentonite, an R600 value of at least 30 is one of the principal reference criteria. R600 alone does not establish complete performance.

YP/PV ratio

Plastic viscosity and yield point are calculated from R600 and R300. The YP/PV ratio helps identify whether yield point is disproportionately high relative to plastic viscosity.

PV = R600 − R300
YP = R300 − PV
YP/PV = YP ÷ PV

The API-oriented reference maximum is YP/PV ≤ 3.

Filtrate volume

Filtration performance shows how effectively the hydrated bentonite system limits liquid passage under the prescribed test condition. The API-oriented reference maximum is 15.0 mL.

Water hardness, salinity, incomplete hydration and inconsistent preparation can materially change the result.

Residue above 75 µm

The wet-sieve procedure measures the mass fraction remaining above 75 µm after controlled dispersion. The API-oriented reference maximum is 4.0 mass %.

This result is a coarse-residue determination and should not automatically be described as sand content because the retained material can contain several mineral species.

Reference comparison is not certification

A laboratory result within the displayed limits is not the same as API certification or API Monogram authorization. Formal qualification must use the applicable current standard, required apparatus and any customer-specific acceptance conditions.