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Line 45: − [[file:evaluating-source-rocks_fig6-9.png|thumb|{{figure number|3}}See text for explanation.]]+ + + + + + + − ==Recognizing good data== − − [[file:evaluating-source-rocks_fig6-10.png|thumb|{{figure number|4}}See text for explanation.]] − − [[file:evaluating-source-rocks_fig6-11.png|thumb|{{figure number|5}}See text for explanation.]] − − [[file:evaluating-source-rocks_fig6-12.png|thumb|{{figure number|6}}See text for explanation.]] − +
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A bimodal distribution or a large spread in the range of measured values will produce a mean R<sub>o</sub> that does not truly represent the maturity of a rock sample.
A bimodal distribution or a large spread in the range of measured values will produce a mean R<sub>o</sub> that does not truly represent the maturity of a rock sample.
==Recognizing good data==
<gallery>
file:evaluating-source-rocks_fig6-9.png|{{figure number|3}}See text for explanation.
file:evaluating-source-rocks_fig6-10.png|{{figure number|4}}See text for explanation.
file:evaluating-source-rocks_fig6-11.png|{{figure number|5}}See text for explanation.
file:evaluating-source-rocks_fig6-12.png|{{figure number|6}}See text for explanation.
</gallery>
An excellent way to recognize high-quality vitrinite reflectance data is to plot it in a histogram. We can have high confidence in the data when a single mode in the distribution curve is tightly clustered about a mean value. The histogram in [[:file:evaluating-source-rocks_fig6-9.png|Figure 3]] is a good example.
An excellent way to recognize high-quality vitrinite reflectance data is to plot it in a histogram. We can have high confidence in the data when a single mode in the distribution curve is tightly clustered about a mean value. The histogram in [[:file:evaluating-source-rocks_fig6-9.png|Figure 3]] is a good example.
==Adequate number of measurements==
==Adequate number of measurements==
A histogram profile of vitrinite reflectance used to estimate the maturity level of a sample must have an adequate number of measurements. Make as many reflectance measurements as possible for a valid R<sub>o</sub> determination for a sample. The histogram in [[:file:evaluating-source-rocks_fig6-10.png|Figure 4]] is an example of a poor profile due to a lack of data. We should not place a high degree of confidence in an R<sub>o</sub> obtained from this sample. A rule of thumb is 40-50 vitrinite readings per sample.
A histogram profile of vitrinite reflectance used to estimate the maturity level of a sample must have an adequate number of measurements. Make as many reflectance measurements as possible for a valid R<sub>o</sub> determination for a sample. The histogram in [[:file:evaluating-source-rocks_fig6-10.png|Figure 4]] is an example of a poor profile due to a lack of data. We should not place a high degree of confidence in an R<sub>o</sub> obtained from this sample. A rule of thumb is 40-50 vitrinite readings per sample.
==Data contaminated by caving==
==Data contaminated by caving==
The histogram in [[:file:evaluating-source-rocks_fig6-11.png|Figure 5]] represents poor-quality vitrinite reflectance data due to contamination by caving. As a result of the drilling process, immature kerogen caved into the bore-hole and mixed with drill cuttings originally containing sparse amounts of vitrinite. The indigenous vitrinite is about 2.5% R<sub>o</sub>. Therefore, it is important to know the type of sample used for vitrinite analysis.
The histogram in [[:file:evaluating-source-rocks_fig6-11.png|Figure 5]] represents poor-quality vitrinite reflectance data due to contamination by caving. As a result of the drilling process, immature kerogen caved into the bore-hole and mixed with drill cuttings originally containing sparse amounts of vitrinite. The indigenous vitrinite is about 2.5% R<sub>o</sub>. Therefore, it is important to know the type of sample used for vitrinite analysis.
==Sample with reworked vitrinite==
==Sample with reworked vitrinite==
The bimodal distribution shown in the histogram in [[:ile:evaluating-source-rocks_fig6-12.png|Figure 6]] represents an indigenous and a reworked population of vitrinite measured in one sample. The reworked population would have been eroded from a more mature provenance and deposited with the indigenous organic matter of this sample.
The bimodal distribution shown in the histogram in [[:file:evaluating-source-rocks_fig6-12.png|Figure 6]] represents an indigenous and a reworked population of vitrinite measured in one sample. The reworked population would have been eroded from a more mature provenance and deposited with the indigenous organic matter of this sample.
==See also==
==See also==