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| isbn = 0-89181-602-X
| isbn = 0-89181-602-X
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Vitrinite reflectance is a measure of the percentage of incident light reflected from the surface of vitrinite particles in a sedimentary rock. It is referred to as %R<sub>o</sub>. Results are often presented as a mean R<sub>o</sub> value based on all vitrinite particles measured in an individual sample.
Vitrinite reflectance is a measure of the percentage of incident light reflected from the surface of [[Thermal maturation#Vitrinite|vitrinite]] particles in a sedimentary rock. It is referred to as %R<sub>o</sub>. Results are often presented as a mean R<sub>o</sub> value based on all vitrinite particles measured in an individual sample.
==Connection between vitrinite and kerogen==
==Connection between vitrinite and kerogen==
The maturation of vitrinite is a kinetic process. The relationship between %R<sub>o</sub> and [[Petroleum generation|hydrocarbon generation]] is dependent on the chemistry of the vitrinite as well as the chemistry of the kerogen.
The maturation of [[Thermal maturation#Vitrinite|vitrinite]] is a [[Kinetics|kinetic]] process. The relationship between %R<sub>o</sub> and [[Petroleum generation|hydrocarbon generation]] is dependent on the chemistry of the vitrinite as well as the chemistry of the [[kerogen]].
==Oil and gas zones==
==Oil and gas zones==
[[file:evaluating-source-rocks_fig6-7.png|300px|thumb|{{figure number|1}}Approximate boundaries for kerogen types I, II, and III. Copyright: Tissot and Welte;<ref>Tissot, B. P., and D.H. Welte, 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p.</ref> courtesy Springer-Verlag.]]
[[file:evaluating-source-rocks_fig6-7.png|300px|thumb|{{figure number|1}}Approximate boundaries for kerogen types I, II, and III. Copyright: Tissot and Welte;<ref>Tissot, B. P., and D.H. Welte, 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p.</ref> courtesy Springer-Verlag.]]
Oil and gas zone boundaries can be established using vitrinite reflectance data. The boundaries are approximate and vary according to kerogen type. [[:file:evaluating-source-rocks_fig6-7.png|Figure 1]] shows the approximate boundaries for kerogen types I, II, and III. Time-temperature relationships and mixing of various sources of organic matter may alter these boundaries.
Oil and gas zone boundaries can be established using vitrinite reflectance data. The boundaries are approximate and vary according to [[kerogen]] type. [[:file:evaluating-source-rocks_fig6-7.png|Figure 1]] shows the approximate boundaries for kerogen types I, II, and III. Time-temperature relationships and mixing of various sources of organic matter may alter these boundaries.
==Misleading data, cautions, and recommendations==
==Misleading data, cautions, and recommendations==
Abimodal distribution or a large spread in the range of measured values produces a mean R<sub>o</sub> value that does not accurately represent the maturity of the rock sample. Variations or errors in vitrinite reflectance measurements may be caused by the following:
Abimodal distribution or a large spread in the range of measured values produces a mean R<sub>o</sub> value that does not accurately represent the maturity of the rock sample. Variations or errors in vitrinite reflectance measurements may be caused by the following:
* Vitrinite composition
* [[Thermal maturation#Vitrinite|vitrinite]] composition
* Incorrect identification of vitrinite particles
* Incorrect identification of vitrinite particles
* [http://wiki.seg.org/wiki/Dictionary:Anisotropy Anisotropy]
* [http://wiki.seg.org/wiki/Dictionary:Anisotropy Anisotropy]
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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.
==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 [[Thermal maturation#Vitrinite|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 [[Thermal maturation#Vitrinite|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 [[: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.
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 [[Thermal maturation#Vitrinite|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==