Changes

The best logs for lithological purposes are those that are (1) most influenced by rock properties and (2) least influenced by fluid properties. The most useful of the commonly available logs are

The best logs for lithological purposes are those that are (1) most influenced by rock properties and (2) least influenced by fluid properties. The most useful of the commonly available logs are

* Gamma ray

* [[Basic open hole tools#Gamma ray|Gamma ray]]

* Spontaneous potential (SP)

* [[Basic open hole tools#Spontaneous potential|Spontaneous potential (SP)]]

* Caliper

* Caliper

* Formation density

* Formation density

* Neutron [[porosity]]

* Neutron [[porosity]]

(For more details on these logs, see [Basic open hole tools]]. Also, [[Difficult lithologies]] covers logging tool response in sedimentary minerals.)

(For more details on these logs, see [[Basic open hole tools]]. Also, [[Difficult lithologies]] covers logging tool response in sedimentary minerals.)

Borehole imaging tools such as the Formation MicroScanner are invaluable for detailed purposes, including bedding character and sedimentary structures, but are much less commonly available. (For more details, see [[Borehole imaging devices]].)

Borehole imaging tools such as the Formation MicroScanner are invaluable for detailed purposes, including bedding character and sedimentary structures, but are much less commonly available. (For more details, see [[Borehole imaging devices]].)

==Gamma ray logs==

==[[Basic open hole tools#Gamma ray|Gamma ray]] logs==

The common radioactive elements—potassium, thorium, and uranium—are normally insignificant in reservoir fluids, whereas they are important components of the rock system, especially of clay minerals. Gamma ray logs are therefore a good indicator of mineralogy.

The common radioactive elements—potassium, thorium, and uranium—are normally insignificant in reservoir fluids, whereas they are important components of the rock system, especially of clay minerals. Gamma ray logs are therefore a good indicator of mineralogy.

* ''Uranium prospecting''. Most of the “uranium” signal actually comes from the tenth decay process in the uranium series, the decay of bismuth-214. This is separated in time from the original uranium by half-lives in excess of 10⁹ years, so the relatively soluble uranium may have moved away during the interim even though the log still records its presence.

* ''Uranium prospecting''. Most of the “uranium” signal actually comes from the tenth decay process in the uranium series, the decay of bismuth-214. This is separated in time from the original uranium by half-lives in excess of 10⁹ years, so the relatively soluble uranium may have moved away during the interim even though the log still records its presence.

==Spontaneous potential (Sp) logs==

==[[Basic open hole tools#Spontaneous potential|Spontaneous potential]] (SP) logs==

===Lithological responses===

===Lithological responses===