Why preparation controls the result
Small differences in bentonite preparation can produce large differences in rheology and filtration. Mixing time, water chemistry, sample mass, temperature, conditioning period and material left on the mixing-cup wall all influence the result.
Reference concentration
A commonly used drilling-grade laboratory suspension contains 22.5 g bentonite in 350 mL water. This equals approximately 64.29 g/L, 64.29 kg/m³ and 22.53 lb/bbl.
This is a laboratory test concentration, not a recommended field dosage.
Preparation sequence
- Measure 350 mL of the specified laboratory water.
- Accurately weigh 22.5 g of bentonite.
- Start the mixer and add the bentonite gradually to reduce agglomeration.
- Maintain the mixing time, mixer condition and geometry required by the method.
- Recover material adhering to the cup wall when required.
- Condition the covered suspension for the prescribed period; API-oriented testing commonly uses at least about 16 hours.
- Re-mix consistently before rheology or filtration measurements.
Water quality
Calcium, magnesium and elevated salinity can suppress hydration. Comparative tests should therefore use the same controlled water and preparation history.
Record the conditions
For defensible comparison, record sample identity, mass, water volume and source, temperature, initial mixing, conditioning and re-mixing time together with R600, R300, filtration and wet-sieve results.