Changes

* ''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.

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

==Spontaneous potential (SP) logs==

===Lithological responses===

===Lithological responses===

====Shale====

====Shale====

SP interpretation depends on first recognizing shale, where fairly constant SP readings form a straight “shale baseline” on the log ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1a]]). Its actual SP value is not significant.

[[Basic open hole tools#Spontaneous potential|Spontaneous potential]] interpretation depends on first recognizing shale, where fairly constant SP readings form a straight “shale baseline” on the log ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1a]]). Its actual SP value is not significant.

====Sandstone====

====Sandstone====