Appendix H

Assessing Natural Clays:
For Use as Drilling Mud

In many situations in remote parts of third world countries, bentonite or polymer is not available. Without these substances, holes often start to cave in and wells can not be successfully completed. Where industry-grade bentonite or polymer is not available, the suitability of locally available clays should be assessed prior to the start of drilling. This can be done using a Free-Standing Swell Test.

What You Need:

  1. One Free Standing Swell Test Kit, containing:
    • 4 - 100 ml.round free-standing graduated cylinders (self-supporting)
    • 1 - Hand Sieve Set:
      • 1 - #73 O-Ring (2 spares included)
      • 1 - 2" diameter 48 Mesh screen cloth
      • 1 - 2" diameter 200 Mesh screen cloth
      • 1 - PVC fines container (male threads) (Genova Products 2" Fitting #71820)
      • 1 - PVC Screen cloth Holder (female threads) (Genova Products 2" Fitting Cleanout body #71619)
    • 49 assorted Ziplock bags (small)
    • 24 1.5 ml. Snap-top bottles
    • 1 - 30 gm. Container of Reference Bentonite
    • 1 - Hand Balance Beam (black wire)
    • ? - 2.0 gm. Reference Weights

  2. The following items should be found on-site:
    • Fresh, clean, "soft" water
    • Clay samples
    • Small, thin spatula
    • Hot oven
    • Grinding stone or rolling pin

  3. If the following items are available, they can be substituted as necessary:
    • Accurate low-weight scale AND/or
    • Balance with 2 gm. weight AND/or
    • Accurate teaspoon-size measuring spoon

Sample Collection:

The best deposits of sodium bentonite are found in areas formed from old volcanic ash deposits. Therefore, if possible, collect clay samples from areas affected by ancient volcanic activity. If these deposits are not found in the country, try collecting clay samples from brackish swamps. Collect several hands-full of each clay to be tested.

Hand Sieve Set Assembly:

To assemble the hand sieve set:
  1. Position the Screen Cloth Holder (larger diameter PVC part) with the treads up.
  2. Place one O-ring into the recess just below the threads.
  3. Place the screen cloth gently on top of the O-Ring, and start twisting the Fines Container (smaller diameter part) into place.
  4. Turn the device over, such that the O-Ring and the screen cloth are visible.
  5. As you tighten the Fines Container, you may need to nudge the O-Ring outward into the recess.
  6. Finish tightening the fines Container, until it is HAND TIGHT (Please use only one O-Ring as there are three O-Rings provided with the Test Kit, but the extra two are intended as spares. You will need to dis-assemble this to remove the fines.)

Sample Preparation:

  1. Take a small amount of the collected sample (1-2 cups). Flatten it as much as possible and break it into small pieces.
  2. Dry it in a hot oven (200-300 degrees F) for 1 hour.
  3. Then crush it as fine as possible.
  4. Place it back in the oven and continue to dry and periodically crush the sample with rolling pins or flat stones.
  5. Periodically place the crushed sample into the hand sieve Set and rap the Sieve Set aggressively until you observe that material no longerfalls through the screen cloth.
  6. Transfer the coarse material back to the grinding step.
  7. Continue this process until the sample is a fine, dry powder which can be easily blown off of an open, outstretched hand.
  8. It is Very Important to thoroughly dry and powder clay samples prior to weighing them since bentonite in chunks weighs only 68 lbs/ft3 while powdered bentonite weighs only 55 lbs/ft3 or 0.88gms/cm3 (there are more air voids in powdered clay).
  9. To remove the ground material from the Sieve Set, first remove any remaining traces of coarse particles from above the screen cloth.
  10. Then twist apart the two PVC pieces carefully to collect the ground powder.
  11. When finished, gently wash and dry the parts of the Sieve Set.
  12. The screen cloth may be dried in the oven, (just a minute or two should do) before grinding the next sample.

Water Source:

  1. Use water which is as pure as possible. Ideally, fresh rainwater should be used. Water should be sediment free and should be as soft as possible (calcium and magnesium can interfere with the swelling of sodium bentonite clays). If possible, use water with a relatively high pH (8-9) to reduce the calcium and magnesium content. If necessary, use soda ash to raise the pH of the water.
  2. If water is run through a water treatment filter to purify it, ensure that it is passed through an activated carbon filter to remove any residual chlorine or iodine prior to the test.
  3. To minimize variability, collect sufficient water in one container to test all the samples and then draw water for each test from the same container.

Free Standing Swell Test Procedure:

  1. Just prior to the test, measure out a 2 gram sample of powdered clay.
    • Option 1:
      • Hang the Balance beam on a branch or a nail.
      • place a 2 gram reference weight on one side of the Balance beam.
      • Punch a hole in one of the included Ziplock Bags, and hang it on the other side of the Balance Beam.
      • Then, fill the Ziplock bag with dry, finely ground sample until the Balance Beam hangs level.

    • Option 2:
      • Estimate the proper weight by measuring 2.3 cm3 clay (0.5 tsp.clay or the equivalent volume of 46 drops of water). This amount of clay would fill TWO of the 1.5 ml. snap-top bottles to just over 2/3 full.
        (If possible, use all four graduated cylinders so that up to four clay samples can be tested at the same time.)
      • Fill the cylinders to the 100 ml. mark with the clean water.
      • Transfer small amounts (0.25 gm.) of the powdered clay onto the surface of the water using the thin spatula. Without Stirring, wait for it to absorb the water and sink on its own. Be patient, this might take as much as 4-5 minutes.)
      • As soon as the last clay has disappeared from the surface of the water, gently drop the next small amount of powdered clay into the cylinder.
      • Continue this process until all of the 2 grams of clay has been added to the sample.


  1. Wait 18 hours, then measure the thickness of the layer of clay sludge on the bottom of the cylinder.
  2. Do not shake or otherwise disturb the sample during this waiting or measuring process.
  3. Clays which are suitable for use as drilling mud should have swelled to the 12-16 ml. (cm3) mark on the cylinder.
  4. If clays have swelled only to the 4-6 ml. mark, they will not effectively coat the side of your borehole during the drilling process and should not be used as the thickening agent.

Last Resort Options:

  1. If you cannot buy bentonite or find any suitable clay deposit, try drilling a borehole in clay soils without any thickening agents.
  2. Drilling in sandy soils has a very low chance of success and will likely collapse prior to the casing, gravel pack and cement grout being in place.
  3. If all other options have failed, try using finely ground seeds from guar plants (guar gum). It must be extremely finely ground (0.0001 microns). as a last resort, try adding potato starch (corn Starch is not quite as good) to the drilling water to enhance the performance of your drilling mud. However, it must be emphasized that these organic starches provide an ideal food source for bacteria and will quickly rot and start fermenting once introduced into the borehole!
  4. Add starch as late in the drilling process as possible and ensure that the well is completed and starch pumped out within 6 hours of it being added to the hole.
  5. Thoroughly rinse the hole with chlorinated water just prior to setting the well screen and casing and float the gravel pack into the hole while running chlorinated water up the annular space.
  6. Once the well is complete, pump it for as long as possible and then shock-chlorinate it before leaving it for the night.


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