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TOPCORP

Core Log Correlation Interactive

Header

At the top of the log is the header. This supplies any pertinent information about the well log, such as the location of the well and the acquisition and processing perimeters. Here we are showing a log that was provided by an exploration and drilling company, so we have blacked out proprietary information.
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Downhole Equipment

This explains the tool configuration. This section lists the tools used in logging and their location along the length of the tool (in feet) by the numbers to the right of the tool. Each abbreviation represents a different tool. For example the HGNS is the highly integrated gamma ray neutron sonde, a device that measures the neutron porosity of the rocks. Abbreviations and acronyms vary by company.
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Track 1

This is the upper scale to Track 1. Track 1 is always the left panel and includes naturally occurring gamma ray, tension, and neutron porosity.
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Track 2

Track 2 is on the right and includes the gas effect, standard resolution formation density, Standard resolution formation photoelectric factor, neutron density, density correlation, and standard resolution density porosity.
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Gamma Ray

Note that gamma ray has three different color representations, a green line, a solid green area and a solid red area. If the gamma ray reading is between 0-200, we will only see a green line. If it is between 200-400 we will see the green line wrap around and include a solid green area. If it is greater than 400, the green line and solid green area will wrap around the curve twice and display a solid red.
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 The blue porosity curve crosses over the red density porosity curve. If they separate or form a gas “cross over,” that suggests different lithology, or the presence of gas. Density porosity will increase and neutron porosity will decrease. Neutron porosity is largely impacted by the number of hydrogen atoms. Gas has a low hydrogen density, so gas zones have a low apparent porosity. On the other hand, the density tool measures formation electrons. A lower number of electrons means a lower density, which indicates a higher porosity.
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 Photoelectric factor value is low here and then increases. This suggests a variation in lithology. Sandstone has lower PE values, while limestone and dolostone (a magnesium-rich limestone) will have high values. Notice that the gamma ray curve decreases. Sandstones will generally have a lower gamma ray signature, and gas is indicated here. A geologist reading this log may see a thin sandstone layer that contains gas that overlies a limestone layer.
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 Photoelectric factor value increases here. This once again suggests a variation in lithology. Notice the gamma ray curve is near a value of 200 API (usually the shale cut off value) and neutron porosity increases. This will likely be interpreted as shale and limestones interlayered.
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 Look at the increase in the caliper curve. The PE curve shows an increase, indicative of shales and limestones. The gamma ray curve increases at the same time as the caliper curve. The neutron density curve also increases and density porosity decreases. This is most likely a weak layer of interbedded shales and limestones that resulted in collapse. If it were a shale layer, there should be a decrease in density, but there isn’t.
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 This is the organic-rich lower unit of the Marcellus Formation as indicated by the high gamma ray signature (>400), lower density, and lower porosity.
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 This shows the transition between the black shale of the Marcellus Formation and the limestone of the underlying Onondaga Formation below it. Notice how the gamma ray signature decreases, but is still greater than 100 API. This suggests to a geologist that the limestone contains amounts of organic-rich shale and a gradual transition between the shale and limestone layers rather than a sharp contact.
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