THE 3
rd
INTERNATIONAL SCIENTIFIC CONFERENCES OF STUDENTS AND YOUNG RESEARCHERS
dedicated to the 99
th
anniversary of the National Leader of Azerbaijan Heydar Aliyev
8
VITRINITE REFLECTANCE ANALYSIS AND ITS APPLICATION
TO BURIAL HISTORY OF BASINS
Zarifa Jabrailova
Baku Higher Oil School
Baku, Azerbaijan
zarifa.jabrayilova.std@bhos.edu.az
Supervisor: Associate Professor Rauf Nadirov
Keywords:
organic maturity, paleogeothermal gradient,
tectonic history, organic
metamorphism
%Ro refers to the reflectance of vitrinite maceral and is used to measure
the degree of organic maturity. Low-rank coals that contain aromatic structures
represent those vitrinite maceral groups, and as coal rank increases, a
significant rise in increase in the aromaticity and condensation is observed,
implying that, higher temperatures cause vitrinite macerals to generate
gaseous hydrocarbons. [1] Vitrinite composition
of the rocks changes
significantly during the heating processes that take place over geological
burial periods, thus, vitrinite reflectance is regarded as a valid method to
evaluate thermal maturity of coal sample, thus it is a reliable measurement
of an energy source. Both thermal and tectonic history of sedimentary basins
are generally preserved by degree of organic metamorphism of carbonaceous
matter, in other words, vitrinite reflectance in carbonaceous elements of
sediments. Models have been developed to relate vitrinite reflectance to
geothermal gradient as a function
of temperature and time; for vitrinite
reflectance values greater than 0.3% and sedimentary basins showing a
constant geothermal gradient over the tectonic history, a relationship
between the logarithm of vitrinite reflectance and depth can be plotted, which
a
gives a linear curve, the slope of which is used to find the geothermal
gradient (°C/km). [2]
For the wells, where maximum temperature is reached at the ultimate
depth, Ro versus depth relationship can be divided into 3 segments, 1) with
the first, uppermost segment where a linear gradient varies between 0.2 %Ro
to 0.6-0.7 %Ro from the surface to a certain depth, 2) the second segment
in the middle with %Ro values up to 1, 3) the lowermost segment where
increases in reflectance are sharper than the first segment, despite the
gradient being linear.
With a decrease
in geothermal gradient, the depth to the inflection rises
systematically, and this enables to plot a diagram demonstrating depth,
reflectance and geothermal gradient, and then using it to identify maximum
burial depth, together with paleogeothermal gradients with a potential
presence of erosion in the wells (either at surface or unconformity). It is