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→Identifying the occurrence of difficult lithologies
==Identifying the occurrence of difficult lithologies==
==Identifying the occurrence of difficult lithologies==
[[file:difficult-lithologies_fig1.png|thumb|{{figure number|1}}M-N crossplot for mineral identification. Copyright: Schlumberger Well Services, 1979.]]
The occurrence of difficult lithologies can be identified from the following sources:
The occurrence of difficult lithologies can be identified from the following sources:
Identifying the occurrence of difficult lithologies from logs can be formidable. Two crossplot techniques are commonly used to identify the occurrence of mineralogies: (1) the M-N crossplot and (2) the MID crossplot.
Identifying the occurrence of difficult lithologies from logs can be formidable. Two crossplot techniques are commonly used to identify the occurrence of mineralogies: (1) the M-N crossplot and (2) the MID crossplot.
===M-N crossplot===
===M-N crossplot===
:<math>\mbox{RHOMAA} = \frac{\rho_{\rm log} - \phi \cdot \rho_{\rm fl}}{1.0 - \phi}</math>
:<math>\mbox{RHOMAA} = \frac{\rho_{\rm log} - \phi \cdot \rho_{\rm fl}}{1.0 - \phi}</math>
[[file:difficult-lithologies_fig3.png|left|thumb|{{figure number|3}}MID plot for mineral identification. © Schlumberger Educational Services, 1989.]]
[[file:difficult-lithologies_fig3.png|thumb|{{figure number|3}}MID plot for mineral identification. © Schlumberger Educational Services, 1989.]]
UMAA can be determined from the chart in [[:file:difficult-lithologies_fig2.png|Figure 2]]. Start by marking the Pe value on the photoelectric portion of the horizontal axis (left side), then go vertically to the bulk density value. Next, move horizontally to the apparent total porosity, and then down to the UMAA value.
UMAA can be determined from the chart in [[:file:difficult-lithologies_fig2.png|Figure 2]]. Start by marking the Pe value on the photoelectric portion of the horizontal axis (left side), then go vertically to the bulk density value. Next, move horizontally to the apparent total porosity, and then down to the UMAA value.