Not all liquids are the same. Some are thin and flow easily. Others are thick and gooey. Honey or corn syrup will pour more slowly than water. A liquid's resistance to flowing is called its viscosity.

Viscosity is an important property of drilling fluids. The more viscous the fluid, the more easily it will suspend cuttings and carry them up to the surface. On the other hand it requires more pressure to pump very viscous fluids and they are harder to wash off the cuttings.

One way to test the viscosity of a liquid is to drop something into it and see how long it takes to sink.

Tools & Materials

To conduct this experiemnt you will need:

• Tall glass or graduated cylinder
• Stopwatch that is accurate to 0.1 or 0.01 seconds
• 20 pebbles, all about the same size and shape
• Water and at least one other liquid. Corn syrup is a good choice.
• Chart like the one below to record your results.

The pebbles we used came from a bag of coarse gravel used for aquariums and sold in pet stores. The pieces were somewhat irregular, and all about the same size: 7 or 8 mm long by about 4 or 5 mm in each of the other two dimensions.

The Experiment

Here's what to do:

1. Fill a graduated cylinder with water and make note of the depth.
2. Drop six pebbles in, one at a time.
3. Use a stop watch to time how long it takes each pebble to reach the bottom.
4. Record your results.

Now repeat the procedure with corn syrup and use a table like this to record your results.

Take a look at our results.

To find out about drilling fluids read Drilling Fluid: Lifeblood of the Well.

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Properties of Liquids

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