Changes

The four methods commonly used for additional core analysis are

The four methods commonly used for additional core analysis are

* Scanning electron microscopy (SEM)

* [[Scanning electron microscopy (SEM)]]

* X-ray diffractometry (XRD)

* X-ray diffractometry (XRD)

* Cathodoluminescence (CL)

* Cathodoluminescence (CL)

* X-ray fluoroscopy (XF)

* X-ray fluoroscopy (XF)

These methods provide important extensions to [[thin section analysis]] and can be tied closely to log response and productivity (see [[Thin section analysis]]). Table 1 summarizes the relative values of each and their limitations.

These methods provide important extensions to [[thin section analysis]] and can be tied closely to log response and productivity. Table 1 summarizes the relative values of each and their limitations.

{| class = "wikitable"

{| class = "wikitable"

|+ {{table number|1}}Special methods for core evaluation

|+ {{table number|1}}Special methods for core evaluation

|-

|-

! Technique

! Technique || General Operating Environment || Data Output || Advantages || Limitations

! General Operating Environment

! Data Output

! Advantages

! Limitations

|-

|-

| SEM

| SEM || 20 kV approx. Vacuum chamber Low M.A. current || 3-D views of secondary Electron images. X-ray spectra for elements with Z> 10. || Pore geometry; grain morphology; diagenetic sequences; microtextures. Ties to some log response and ''φ-k'' analyses. ||

| 20 kV approx. Vacuum chamber Low M.A. current

*Sample size limited.   

| 3-D views of secondary Electron images. X-ray spectra for elements with Z> 10.

*High organic content frequently causes short filament life.   

| Pore geometry; grain morphology; diagenetic sequences; microtextures. Ties to some log response and ''φ-k'' analyses.

*Carbon or Au/Pd coating generally needed.   

| * Sample size limited.  * High organic content frequently causes short filament life.  * Carbon or Au/Pd coating generally needed.  * Shielding required.

*Shielding required.

 

|-

|-

| XRD

| XRD || 10–40kV X-ray wavelength fixed. Low M.A. current || Diffraction patterns or digital files for comparison to “standards” files. || Mineralogy on semiquantitative scale. Best method for determining clay mineralogy. Does not require microscope. ||

| 10–40kV X-ray wavelength fixed. Low M.A. current

*Sample prep.powder.   

| Diffraction patterns or digital files for comparison to “standards” files.

*Abundances based on measured intensities and areas.

| Mineralogy on semiquantitative scale. Best method for determining clay mineralogy. Does not require microscope.

| * Sample prep.powder.  * Abundances based on measured intensities and areas.

 

|-

|-

| CL

| CL || 12–20kV Vacuum chamber on microscope. Also visible on microprobe. Low M.A. current || Photographs: intensity relates to activator. Sensitizer and quencher ion content or lattice defect. || In carbonates, color zoning can be related to complex Eh-pH history. In clastics, lattice defect and activator ion content used in provenance and para-genesis studies. ||

| 12–20kV Vacuum chamber on microscope. Also visible on microprobe. Low M.A. current

*High Fe(II), Ni(II), Co(II) content quenches CL.   

| Photographs: intensity relates to activator. Sensitizer and quencher ion content or lattice defect.

*Samples require special epoxy for prep.   

| In carbonates, color zoning can be related to complex Eh-pH history. In clastics, lattice defect and activator ion content used in provenance and para-genesis studies.

*Color emitted may extinguish at high Mn concentration.   

| * High Fe(II), Ni(II), Co(II) content quenches CL.  * Samples require special epoxy for prep.  * Color emitted may extinguish at high Mn concentration.  * Vacuum leaks quench CL.  * Shielding required.

*Vacuum leaks quench CL.   

 

*Shielding required.

|-

|-

| XF

| XF || ±40 kV General current 3–200 M.A. || Photoradiographs video imaging. || Image often defines hidden character of sample, e.g., may show directional [[porosity]] and flow boundaries, internal structures of fossils. ||

| ±40 kV General current 3–200 M.A.

*Voltage increase decreases contrast in image.   

| Photoradiographs video imaging.

*Shielding required.   

| Image often defines hidden character of sample, e.g., may show directional [[porosity]] and flow boundaries, internal structures of fossils.

*Carbonate photos often lack detail because mineral variety simpler than siliciclastics.   

| * Voltage increase decreases contrast in image.  * Shielding required.  * Carbonate photos often lack detail because mineral variety simpler than siliciclastics.  * Samples must be relatively thin.

*Samples must be relatively thin.

|}

|}

==Scanning electron microscopy (SEM)==

==Scanning electron microscopy (SEM)==

<gallery>

<gallery mode=packed heights=200px widths=200px>

file:sem-xrd-cl-and-xf-methods_fig1.png|{{figure number|1}}Schematic drawing of a common scanning electron microscope showing how the sample is “iluminated” by an electron beam and amplified for viewing by the operator.

file:sem-xrd-cl-and-xf-methods_fig1.png|{{figure number|1}}Schematic drawing of a common scanning electron microscope showing how the sample is “iluminated” by an electron beam and amplified for viewing by the operator.

file:sem-xrd-cl-and-xf-methods_fig2.png|{{figure number|2}}X-ray diffraction configuration. Knowledge of the wavelength (X) and angle of incidence allows the ''d'' spacing to be calculated.

file:sem-xrd-cl-and-xf-methods_fig2.png|{{figure number|2}}X-ray diffraction configuration. Knowledge of the wavelength (X) and angle of incidence allows the ''d'' spacing to be calculated.

file:sem-xrd-cl-and-xf-methods_fig3.png|{{figure number|3}}X-ray diffraction patterns.

file:sem-xrd-cl-and-xf-methods_fig3.png|{{figure number|3}}X-ray diffraction patterns.

file:sem-xrd-cl-and-xf-methods_fig4.png|{{figure number|4}}Schematic drawing showing how a typical cathodoluminescence system works. Depending on the manufacturer, the location of the cathode tube may differ.]]

file:sem-xrd-cl-and-xf-methods_fig4.png|{{figure number|4}}Schematic drawing showing how a typical cathodoluminescence system works. Depending on the manufacturer, the location of the cathode tube may differ.

file:sem-xrd-cl-and-xf-methods_fig5.png|{{figure number|5}}A photomicrograph taken under cathodoluminescence showing concentric zoning in dolomite cement. High Mn⁺² dolomite shows up as bright bands and higher Fe⁺² dolomite as dark bands. Copyright: W. J. Myers.

file:sem-xrd-cl-and-xf-methods_fig5.png|{{figure number|5}}A photomicrograph taken under cathodoluminescence showing concentric zoning in dolomite cement. High Mn⁺² dolomite shows up as bright bands and higher Fe⁺² dolomite as dark bands. Copyright: W. J. Myers.

file:sem-xrd-cl-and-xf-methods_fig6.png|{{figure number|6}}(a) X-ray fluoroscopy slab photograph and (b) plane light slab photograph of a Pennsylvanian sandstone from Oklahoma.

file:sem-xrd-cl-and-xf-methods_fig6.png|{{figure number|6}}(a) X-ray fluoroscopy slab photograph and (b) plane light slab photograph of a Pennsylvanian sandstone from Oklahoma.

Nonminerals such as solid hydrocarbons or glass cannot be identified by XRD because they lack sufficient internal structure.

Nonminerals such as solid hydrocarbons or glass cannot be identified by XRD because they lack sufficient internal structure.

Determination of bulk rock mineralogy is obtained from combined diffraction analysis of bulk powder and oriented mounts. Powder mounts are best for identification of nonplaty minerals. Platy minerals are best analyzed in slurries dried on metal, glass, or ceramic holders. This is especially true for clays with particle sizes ≤5 μm. Abundances are then determined by measuring peak intensity or half area for the diffraction peaks of the major three to five diffraction peaks of each mineral ([[:file:sem-xrd-cl-and-xf-methods_fig3.png|Figure 3]]). A limitation of this method is the inability to determine abundances of mineral species (such as quartz from chert) or polymineral grains (such as granite from separate feldspar and quartz).

Determination of bulk rock mineralogy is obtained from combined diffraction analysis of bulk powder and oriented mounts. Powder mounts are best for identification of nonplaty minerals. Platy minerals are best analyzed in slurries dried on metal, glass, or ceramic holders. This is especially true for clays with particle sizes ≤5 μm. Abundances are then determined by measuring peak intensity or half area for the diffraction peaks of the major three to five diffraction peaks of each mineral ([[:file:sem-xrd-cl-and-xf-methods_fig3.png|Figure 3]]). A limitation of this method is the inability to determine abundances of mineral species (such as [[quartz]] from [[chert]]) or polymineral grains (such as granite from separate feldspar and quartz).

==Cathodoluminescence (CL)==

==Cathodoluminescence (CL)==

In CL, electrons from a cold cathode discharge tube strike a rock surface in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig4.png|Figure 4]]). In a strong vacuum, energy imparted to electrons in activator ions within the grain causes luminescence. The principle activator ions are manganese and lead.<ref name=pt05r107>Machel, H-G., 1985, Cathodoluminescence in calcite and dolomite and its chemical interpretation: Geoscience Canada, v. 12, p. 139–147.</ref> Concentrations need be in the 100 ppm range to affect the grain. Other rare earth elements such as dysprosium are also activators. Ferric iron (+3) is the most common quenching ion. The emitted color, when observed, shows the zonations in activator ion concentrations related to the type of crystallization or thermal histories of the host minerals ([[:file:sem-xrd-cl-and-xf-methods_fig5.png|Figure 5]]). Lattice defect structures in quartz are also thought to cause some CL in quartz.

In CL, electrons from a cold cathode discharge tube strike a rock surface in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig4.png|Figure 4]]). In a strong vacuum, energy imparted to electrons in activator ions within the grain causes luminescence. The principle activator ions are manganese and lead.<ref name=pt05r107>Machel, H-G., 1985, Cathodoluminescence in calcite and dolomite and its chemical interpretation: Geoscience Canada, v. 12, p. 139–147.</ref> Concentrations need be in the 100 ppm range to affect the grain. Other rare earth elements such as dysprosium are also activators. Ferric iron (+3) is the most common quenching ion. The emitted color, when observed, shows the zonations in activator ion concentrations related to the type of crystallization or thermal histories of the host minerals ([[:file:sem-xrd-cl-and-xf-methods_fig5.png|Figure 5]]). Lattice defect structures in [[quartz]] are also thought to cause some CL in quartz.

The most frequent application of CL is in carbonate diagenesis (e.g.,  Machel,<ref name=pt05r107 /> Myers<ref name=pt05r120>Myers, W. J., 1978, Carbonate cements—their regional distribution and interpretation in Mississippian limestones of southwestern New Mexico: Sedimentology, v. 25, p. 371–399.</ref>). As has been shown by Sippel,<ref name=pt05r147>Sippel, R. T., 1968, Sandstone petrology, evidence from luminescence petrography: Journal of Sedimentary Petrology, v. 38, p. 530–554.</ref> it is also useful in determining paragenesis of siliciclastic rocks. It is particularly useful in interpreting original composition and texture in recrystallized or dolomitized strata.

The most frequent application of CL is in [[carbonate diagenesis]] (e.g.,  Machel,<ref name=pt05r107 /> Myers<ref name=pt05r120>Myers, W. J., 1978, Carbonate cements—their regional distribution and interpretation in Mississippian limestones of southwestern New Mexico: Sedimentology, v. 25, p. 371–399.</ref>). As has been shown by Sippel,<ref name=pt05r147>Sippel, R. T., 1968, Sandstone petrology, evidence from luminescence petrography: Journal of Sedimentary Petrology, v. 38, p. 530–554.</ref> it is also useful in determining paragenesis of siliciclastic rocks. It is particularly useful in interpreting original composition and texture in recrystallized or dolomitized strata.

==X-ray fluoroscopy (XF)==

==X-ray fluoroscopy (XF)==

[[Category:Laboratory methods]]

[[Category:Laboratory methods]]