Changes

==Example density-neutron log==

==Example density-neutron log==

[[file:predicting-reservoir-system-quality-and-performance_fig9-31.png|thumb|{{figure number|1}}Example log recorded in sandstone units.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-30.png|thumb|{{figure number|1}}Example log recorded in sandstone units.]]

The example log in [[:file:predicting-reservoir-system-quality-and-performance_fig9-31.png|Figure 1]] was recorded in sandstone units. Where the density and neutron logs nearly track together, the formation lithology normally is assumed to be sandstone (in the figure below). The slight separations may be due to changes in lithology as in more shale/clay. Where the density and neutron logs separate, either the lithology is different (neutron porosity > density porosity) from the recorded lithologic units (points 1 and 5) or gas is present (points 2, 3, and 4). A density–neutron crossplot resolves the separation problem (see [[:file:predicting-reservoir-system-quality-and-performance_fig9-31.png|Figure 1]]).

The example log in [[:file:predicting-reservoir-system-quality-and-performance_fig9-30.png|Figure 1]] was recorded in sandstone units. Where the density and neutron logs nearly track together, the formation lithology normally is assumed to be sandstone (in the figure below). The slight separations may be due to changes in lithology as in more shale/clay. Where the density and neutron logs separate, either the lithology is different (neutron porosity > density porosity) from the recorded lithologic units (points 1 and 5) or gas is present (points 2, 3, and 4). A density–neutron crossplot resolves the separation problem (see [[:file:predicting-reservoir-system-quality-and-performance_fig9-31.png|Figure 2]]).

==Using a density–neutron crossplot==

==Using a density–neutron crossplot==

===Example density–neutron crossplot===

===Example density–neutron crossplot===

[[file:predicting-reservoir-system-quality-and-performance_fig9-30.png|thumb|{{figure number|9-30}}.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-31.png|thumb|{{figure number|2}}Example density-neutron crossplot.]]

 

[[:file:predicting-reservoir-system-quality-and-performance_fig9-31.png|Figure 2]] is an example density-neutron crossplot. Points 1–5 are from the log (Figure 9-30). Points 2, 3, and 4 are from a zone that shows crossover. Crossover occurs when the density log reads higher than the neutron log in a zone of the same lithology as the log matrix lithology, i.e., sandstone. Point 2 has the greatest crossover; Point 4, the least. Once completed, the well from which this log was taken showed Point 2 to be in a gas reservoir, Point 3 to be in light oil reservoir, and Point 4 to be in a zone with residual oil.

Porosities corrected for gas effect are 24%, 25%, and 28%. Points 1 and 5 are in shale zones, even though they plot as dolomite. They are shale reference points for this interval of the log.

Porosities corrected for gas effect are 24%, 25%, and 28%. Points 1 and 5 are in shale zones, even though they plot as dolomite. They are shale reference points for this interval of the log.