well known. On the other hand, the density of clay minerals such as mudstone is highly variable, depending on depositional environment, overburden pressure, type of clay mineral and many other factors. It can vary from 2.1 (montmorillonite) to 2.76 (chlorite) so this tool is not as useful for determining their porosity. A fluid bulk density of 1 g/cm3 is appropriate where the water is fresh but highly saline water has a slightly higher density and lower values should be used for hydrocarbon reservoirs, depending on the hydrocarbon density and residual saturation. In some applications hydrocarbons are indicated by the presence of abnormally high log porosities. See also Sonic logging References Well logging Drilling technology