2 research outputs found
Methane and Carbon Dioxide Adsorption on Illite
The adsorption of
CH<sub>4</sub> and CO<sub>2</sub> onto illitic
clay was investigated at the temperatures 298, 313, 328, 358, and
423 K (25, 40, 55, 85, and 150 °C) over a range of pressures
up to 50 MPa using grand canonical Monte Carlo (GCMC) simulations.
Our simulation results showed spontaneous and exothermic adsorption
behavior of illite for CH<sub>4</sub> and CO<sub>2</sub> with enthalpy
changes of −3.50 kJ/mol and −25.09 kJ/mol, respectively.
Our results indicated that the interlayer counter cations (K<sup>+</sup>) play an important role in CO<sub>2</sub> adsorption. Methane adsorption
is mainly affected by the clay surface layers rather than the interlayer
counter cations. The density and volume of CH<sub>4</sub> and CO<sub>2</sub> in their adsorbed phase at saturation were extrapolated from
the linear portion of the excess adsorption isotherm. The resulting
values were compared with available experimental data, and possible
factors causing inconsistency were described. We discussed some issues
associated with the Langmuir fit to experimental excess adsorption
data in the case of low pressures. Our findings may provide some insights
into gas adsorption behavior in illite-bearing shales
Pyrite Dissolution in the Cretaceous Yogou Formation of the Niger (Chad) Basin: Implications for Basin Evolution under a Rift Tectonic Setting
This is the first study of pyrite minerals in the entire
West and
Central African Rift System (WCARS). Several polished organic-rich
core samples from the Cretaceous Yogou Formation of the Niger (Chad)
Basin located in the WCARS were investigated for their pyrite content
using FE-SEM and SEM-EDS imaging techniques. An attempt was made to
classify the types and provenance of the pyrites and to highlight
the control of rift fractures on the oxidation and dissolution of
pyrites in the region. Three major types of pyrites are present in
the studied formation, including euhedral pyrite (EPy) crystals, pyrite framboids (FPy), and sunflower
pyrites (SPy). A statistical analysis of 307 FPy shows that the framboids are diagenetically formed with
an average diameter of 6.61 μm. SPy is present
in a relatively low amount compared to framboids. The pyrites underwent
a variety of diagenetic modifications, from mechanical compaction
to oxidation, dissolution, and recrystallization. Unoxidized pyrites
primarily contain Fe, S, and C, but oxidized pyrites also contain
O, Al, and Si. There is a strong correlation between the fractures
and the spatial distribution of the physicochemical alteration of
the pyrite in the study. Dissolution in relatively deep-buried samples
occurs mainly along fracture planes. The fractures provide a pathway
for oxidants and other metal elements to reach the pyrites. The pattern
of pyrite dissolution reflects the timing of fracture formation and
fracture activities as a purveyor or drainage for fluids in the organic-rich
samples investigated. The pyrites are associated intimately with organic
matter (OM); thus, the relationship between the fracture and the pyrites’
transformation is significant in the assessment of organic matter
preservation at deep-burial depth