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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. |
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− | [[file:evaluating-source-rocks_fig6-9.png|thumb|{{figure number|3}}See text for explanation.]]
| + | ==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> |
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− | ==Recognizing good data==
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| 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. |
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− | [[file:evaluating-source-rocks_fig6-10.png|thumb|{{figure number|4}}See text for explanation.]]
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| ==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. |
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− | [[file:evaluating-source-rocks_fig6-11.png|thumb|{{figure number|5}}See text for explanation.]]
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| ==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. |
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− | [[file:evaluating-source-rocks_fig6-12.png|thumb|{{figure number|6}}See text for explanation.]]
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| ==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. |
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| ==See also== | | ==See also== |