Changes

===Property measured===

===Property measured===

Measured density is the sum of the rock system density and the pore fluid system density. Density values can therefore be used directly to identify lithology only when the porosity is insignificant. In porous rocks, density must be interpreted in combination with neutron or other porosity logs.

Measured density is the sum of the rock system density and the pore fluid system density. Density values can therefore be used directly to identify lithology only when the porosity is insignificant. In porous rocks, density must be interpreted in combination with neutron or other porosity logs.

====Evaporites====

====Evaporites====

Individual evaporitic minerals (such as anhydrite, halite, sylvite, and carnallite) have well-defined densities and generate straight-line density logs with little variation (Figure 2).

Individual evaporitic minerals (such as anhydrite, halite, sylvite, and carnallite) have well-defined densities and generate straight-line density logs with little variation ([[:file:quick-look-lithology-from-logs_fig2.png|Figure 2]]).

 

[[file:quick-look-lithology-from-logs_fig2.png|thumb|{{figure number|2}}Characteristic log signatures for a carbonate and evaporite sequence. Hole conditions are good.]]

====Coal====

====Coal====

Coals are variable but always significantly lighter than 2 g/cm³. Thin beds give a pronounced density spike, but may not resolve a true density reading (Figure 1c). Note that deep washouts also give low-density spikes.

Coals are variable but always significantly lighter than 2 g/cm³. Thin beds give a pronounced density spike, but may not resolve a true density reading ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1c]]). Note that deep washouts also give low-density spikes.

====Ironstone====

====Ironstone====

====Shale====

====Shale====

Densities of shales vary between 2.2 and 2.65 g/cm³ or more, increasing with compaction induced by age and depth of burial (Figure 1). Overpressured shales, in which some of the overburden load is borne by pore fluid, are undercompacted and have low densities relative to normally pressured shales at similar depths.

Densities of shales vary between 2.2 and 2.65 g/cm³ or more, increasing with compaction induced by age and depth of burial ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1]]). Overpressured shales, in which some of the overburden load is borne by pore fluid, are undercompacted and have low densities relative to normally pressured shales at similar depths.

==Photoelectric absorption (Pe) logs property measured==

==Photoelectric absorption (Pe) logs property measured==