Drilling Fluids QA/QC - Quality Control of Freshwater

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The following procedures shall be carried out, or fully supervised, by the Mud Engineer to determine the salinity of freshwater delivered to the rig. This is essential to prevent inadequate yielding of bentonite and unwanted acceleration of freshwater cement slurries.

The salinity level determination of the water should be carried out using the DS meter and then checked with the chemical analysis if high salinity levels (>200 ppm NaCI) are indicated.

 The mud engineer shall check the water quality for chloride and calcium contamination.

Sampling

The water shall be collected in clear glass/plastic bottles, having a snug-fitting ground glass stopper/screw cap. (Company to send bottles to rig).

Bottles shall be clean and rinsed out by filling three times with water before the sample is taken.

The water to be sampled shall be allowed to run to waste for at least two minutes or such a time that impurities from pipes and hoses are removed, before a representative sample can be taken.

Contamination of the water sample during and after sampling by hand, dirt, etc. shall be avoided.

After collection of the sample, the bottle shall be labelled stating the source, date and time of collection and all other details for easy reference when despatched or retained.

Determination of Salinity of Water (fresh/industrial water) by Chemical Analysis

Reagents:

Standard Silver Nitrate solution. 0.1 N

Potassium Chromate indicator solution

Sodium Hydroxide solution. 0.1 N

Sulphuric Acid solution 0 1 N

1. Take 100 mls of water from sample bottle and POUR into a 500 ml Erlenmeyer flask.

2. Check pH of sample using pH-paper of the required range or pH meter.

3. If required, neutralize the sample using 0.1 N Sulphuric Acid to lower pH or 0.1 N Sodium Hydroxide to increase pH until pH is between 6.5 and 8 5.

4. Add 10 drops of Potassium Chromate indicator, swirling the Erlenmeyer flask.

5. Titrate with 0.1 N Silver Nitrate solution, swirling the Erlenmeyer flask constantly, until the first permanent red tinge colour deviation from the pure yellow of the suspension is obtained.

6. Calculate salinity using the following equation:

Salinity (as NaCI)    ppm = mls Silver Nitrate x 58 5

7. Repeat test to ensure reliability of result.

Action to be Taken in the Event of Unacceptable Water Quality

In the event that the measured water salinity is in excess of 200 ppm NaCI, the Mud Engineer/Drilling Supervisor/Barge Engineer shall ensure that:

  • the rejected material is not transferred.
  • a five litre sample is sent to the Mud and Cement Laboratory stating the following:
  • date
  • rig
  • supply vessel/truck
  • salinity level detected
  • any other relevant information.

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