Changes

* Neutron [[porosity]]

* Neutron [[porosity]]

(For more details on these logs, see the chapter on “[[Basic open hole tools]]” in Part 4. Also, the chapter on “[[Difficult lithologies]]” in Part 4 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<xref ref-type="fn" rid="LogLithologyfn1">¹</xref> are invaluable for detailed purposes, including bedding character and sedimentary structures, but are much less commonly available. (For more details, see the chapter on “[[Borehole imaging devices]]” in Part 4.)

Borehole imaging tools such as the Formation MicroScanner<xref ref-type="fn" rid="LogLithologyfn1">¹</xref> 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==

==Gamma ray logs==

* Clay added later due to bioturbation or mechanical infiltration at the top of a gravel may create a bell shape.

* Clay added later due to bioturbation or mechanical infiltration at the top of a gravel may create a bell shape.

(For more details on using log shape to interpret depositional environment, see the chapter on “Lithofacies and Environmental Analysis of Clastic Depositional Systems” in Part 6.)

(For more details on using log shape to interpret depositional environment, see [[Lithofacies and environmental analysis of clastic depositional systems]].)

===Problems and exceptions===

===Problems and exceptions===

====Sandstone====

====Sandstone====

The potential differences around a sand/shale contact deflect the SP from the shale baseline. The deflection is negative for a normal salinity contrast (borehole fresher than formation). Little change occurs within a sand interval, so a clean sand shows a straight-line “sand line” ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1c]]). (For more details on SP shale and sand baselines, see the chapter on “Determination of Water Resistivity” in Part 4.)

The potential differences around a sand/shale contact deflect the SP from the shale baseline. The deflection is negative for a normal salinity contrast (borehole fresher than formation). Little change occurs within a sand interval, so a clean sand shows a straight-line “sand line” ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1c]]). (For more details on SP shale and sand baselines, see [[Determination of water resistivity]].)

====Tight rocks====

====Tight rocks====