Error in measuring rock porosity by Archimedes method

[Peter Persoff]

The standard way to measure porosity of a rock is to get the pores completely saturated with water, then weigh the rock immersed in water and again in air (there are modified balances for this). Using Archimedes' principle, you then can determine the volume of the rock. Then you dry the rock completely and weigh it again (only in air). The water weight lost gives you the pore space in the rock. Divide this into the total volume and you get the porosity.

A major source of error is that when you weigh the rock after taking it out iof the water you have to blot the outside surface dry. Not dry enough and you are weighing some exterior water. Too dry and you will suck some of the water out of the pores and the rock is no longer saturated.

What I am looking for is a textbook or other publication that tells the amount of error to be expected from this source. Anyone with information or experience with this method is welcome to reply.

 

[Ophiolite]

The standard way? What ever happened to mercury porosimeters?

 

[ravenprp]

There are a few potential sources of error in using the Archimedes method to measure rock porosity. One major source, as mentioned in the content, is the potential for not properly drying the exterior surface of the rock. This could result in either over or underestimating the water weight lost and therefore the porosity of the rock.

Another potential source of error is the assumption that all pores are completely filled with water. In reality, some pores may be filled with air or other fluids, leading to an inaccurate measurement of the volume of the rock. Additionally, the method may not work well for rocks with very small or irregularly shaped pores.

As for the amount of error to be expected from these sources, it would likely vary depending on the specific characteristics of the rock being measured and the technique used. It would be best to consult a textbook or published study on the Archimedes method for rock porosity for more specific information. Alternatively, reaching out to experts in the field who have experience with this method may also provide valuable insights.