Changes

! Lithology || Gamma Ray Values (in API units)

! Lithology || Gamma Ray Values (in API units)

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|-

| [[Sandstone]] (quartz) || 15–30 (rarely to 200)

| [[Sandstone]] ([[quartz]]) || 15–30 (rarely to 200)

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|-

| [[Limestone]] || 10–40

| [[Limestone]] || 10–40

====Sandstone====

====Sandstone====

Quartz should read 1.7 to 1.8 barns/electron, but most other minerals can raise the value substantially. Because they are usually present, the log is of limited value.

[[Quartz]] should read 1.7 to 1.8 barns/electron, but most other minerals can raise the value substantially. Because they are usually present, the log is of limited value.

====Limestone====

====Limestone====

====Sandstone (Oil or Water Filled)====

====Sandstone (Oil or Water Filled)====

Clean quartz sandstones give the typical two-division neutron-density cross-over with density to the left of neutron ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1]]). The addition of some clay (forming shaly sandstone) increases the neutron reading, reducing log crossover or even reversing it to create separation. Check natural gamma ray for evidence of increasing clay.

Clean [[quartz]] sandstones give the typical two-division neutron-density cross-over with density to the left of neutron ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1]]). The addition of some clay (forming shaly sandstone) increases the neutron reading, reducing log crossover or even reversing it to create separation. Check natural gamma ray for evidence of increasing clay.

Heavier components such as mica increase the density, reducing log cross-over or even reversing it to create separation. Check spectral gamma ray to distinguish the following:

Heavier components such as mica increase the density, reducing log cross-over or even reversing it to create separation. Check spectral gamma ray to distinguish the following: