The two important factors that affect the metamorphic
processes of fossil energy (coal or petroleum) are temperature and time.
Vitrinite reflectance is used to objectively reflect the maturation of
sedimentary organic matter. There are three temperature measurement methods
without using vitrinite reflectance and four temperature calculating methods
using vitrinite reflectance only. The vitrinite reflectance gradient of coal is
generally lower than 0.06%/100m in plutonic metamorphism. The vitrinite reflectance
gradient of the regional magmatic thermal metamorphic coal is higher up to
0.27~0.57%/100m in Pingdingshan, China.
Wu established A metamorphic thermodynamic equation for coal
(MTEC), which contains ternary functions (temperature, time and vitrinite reflectance),
so the third quantity can be found on the premise that there are any two known
quantities. The results of ternary equations can be expressed in tabular
methods, graphing methods, and analytical methods. The MTEC is chosen as the
comparison value, and the temperature obtained through other calculating
methods as the basic value. The relative error, the average relative error, and
the standard deviation are used to verify the applicability of MTEC. A
time-to-temperature ratio t/T is designed to evaluate the relative contribution
between the metamorphic temperature to the contribution of the extended time.
There are three geological periods that can produce from low-rank coal
(long-flame coal) to high-rank coal (anthracite) in China. In the three coal-forming
periods, the time-to-temperature ratio was t/T>1 under all vitrinite
reflectance examined, and the effect of increasing the temperature by 1°C was
greater than that of extending the time by 1 million years, that is, the
contribution of temperature was much greater than the contribution of extending
time. During the same coal-forming period, with the increase of vitrinite
reflectivity, the effect of temperature decreased significantly. At the same
vitrinite reflectance, the significant effect of temperature decreases with the
youth of coal-forming stage.
The MTEC is more convenient and accurate than diagrams and
is more in line with the scientific principles of coal metamorphism. Because it
is very difficult to directly solve the paleo geological time using MTEC, an
iterative algorithm is used to solve this problem. Control the iteration
process with the difference between the new and previous values so that the
iteration process does not run endlessly. The golden ratio value of 0.618 is
used to optimize the relationship between the value of the new iteration and
the value of the previous iteration.
MTEC uses the calculated table to confirm that Xiao
Xianming's simulation of vitrinite reflectance gradient and paleo geothermal
temperature gradient shows that (1) vitrinite reflectance gradient is
positively correlated with temperature gradient under fixed time and
reflectance conditions. (2) In the case of fixed time and vitrinite reflectance
gradient. The temperature gradient is negatively correlated with vitrinite
reflectance. At the same time, it is also concluded that (3) in the case of
fixed temperature gradient and vitrinite reflectance gradient. Vitrinite
reflectance gradient is negatively correlated with time.
According to the measured static vitrinite reflectance and
the corresponding burial depth of 26 coal samples in 4 groups of boreholes in
the Huaibei coalfield, the temperature of 26 samples was calculated by MTEC at
a time of 137 million years. Vitrinite reflectance gradient from measured
vitrinite reflectance and burial depth. The results showed that Taoyuan and
Xuton both have vitrinite reflectance of 0.057%/100m. They belong to plutonic
metamorphism. But Qidong and Linhuan have a vitrinite reflectance of
0.105%/100m and 0.100%/100m, respectively. They belong to regional magmatic
metamorphism. But plotting all 22 T/R0 ratios as vitrinite reflectance gradient
vs temperature gradient can create a straight line with a slop of 56.3 °C/%,
which means that the temperature-reflectance gradient ratio T/R0>50, and the
metamorphism of Huaibei coalfield is the plutonic metamorphism.
The metamorphic thermodynamic equation for petroleum (MTEP)
has the same functional form as the metamorphic thermodynamic equation for coal
(MTEC) due to the similarity of both metamorphisms. Therefore, MTEP and MTEC
have three variables, temperature, time and vitrinite reflectance, and have the
exact same mathematic formation with different parameters. According to the
dissimilarity of coal and petroleum, four parameters are determined to be
completely different or partially different in the MTEP and MTEC two equations.
The measurement data from an exploratory well in Indonesia provide sufficient
data to validate the MTEP. Judging by the error of the measured reflectance of
the stationary body, it is more reasonable to use the temperature judgment in
this book. For the 15 measurement points of the Tertiary Period, the average
relative error of temperature is <8.1% and the standard deviation of the
relative error is <5.4%. For the 14 measurement points of the Mesozoic Era,
the average relative error of temperature is <3.1% and the standard
deviation of the relative error is <2.2%. This book translates a well-known
hypothesis “either an increase in temperature of 10℃ or a doubling
of the exposure time will double the rate of reaction”
into a series of mathematical equations. And with the example of actual
calculations, it is fully and beautifully demonstrated. For the 10-verification
calculations of the Tertiary Period, the average relative error of temperature
is <5.7% and the standard deviation of the relative error is <0.87%. For
the 9-verification calculations of the Mesozoic Era, the average relative error
of temperature is <8.3% and the standard deviation of the relative error is
<0.13%. EXCEL and METLAB are used for simple calculations and drawing
figures.
Author (s) Details
Li Dong
Xi'an Siyuan University, Xi'an, Shaanxi, 710038, China.
ZHANG Xuemei
Xi'an Siyuan University, Xi'an, Shaanxi, 710038, China.
Please see the book here:- https://doi.org/10.9734/bpi/mono/978-93-49970-74-8
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