Thermal Evolutions and Resulting Microstructural Changes in Kerogen-Rich Marcellus Shale (original) (raw)
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Microstructural characterisation of organic-rich shale before and after pyrolysis
Understanding of the initiation and development of fractures in organic-rich shales is crucially important as fractures could drastically increase the permeability of these otherwise lowpermeable rocks. Fracturing can be induced by rapid decomposition of organic matter caused by either natural heating, such as emplacement of magmatic bodies into sedimentary basins, or thermal methods used for enhanced oil recovery.
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The study of organic-rich carbonate-containing shales after heating is an important task for the effective application of in-situ thermal kerogen conversion technologies implemented for these types of rocks. This research was conducted to study changes in the rocks of the Domanik Formation after high-temperature treatment, taking into account the nature of structural changes at the micro level and chemical transformations in minerals. The sample of organic-rich carbonate-containing shales of the Domanik Formation was treated in stages in a pyrolizer in an inert atmosphere in the temperature range of 350–800 °C for 30 min at each temperature. By means of X-ray powder diffractometry (XRPD), HAWK pyrolysis, light and scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and computed micro-tomography, the characteristics of the rock before and after each heating stage were studied. The results showed significant alteration of the mineral matrix in the temperatu...
Thermal Behavior of Raw Oil Shale and Its Components
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In this study, the thermal behavior of dawsonite, nahcolite, quartz, dolomite, albite, illite, analcime, kerogen and raw oil shale samples is discussed. Thermal Gravimetric Analysis (TGA), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) were used to study the thermal properties of the samples. The DSC dynamic experiments were performed in CO 2 and N 2 atmospheres. The influence of purge gases on the thermal decomposition of kerogen, dawsonite and nahcolite was investigated. In the DSC experiments, the heating rate did not change the decomposition mechanism of both dawsonite and nahcolite and the Tp (the sample temperature at which the maximum deflection in the DSC curve is recorded) of dawsonite and nahcolite could be moved to higher temperatures by purging CO 2 .
Pyrolytic behaviour of Spanish oil shales and their kerogens
Journal of Analytical and Applied Pyrolysis, 2000
A comparative study of the thermal behaviour of selected Spanish oil and their kerogen concentrates has been carried out. The oil shales differ in geological age, depositional environment, source location and degree of maturity. The influence of the amount and composition of mineral matter in the thermal behaviour of the oil shales and its influence on the amount of hydrocarbons released has been assessed. In mineral matter-rich samples, the mineral matter is responsible for a delay in the hydrocarbon generation during thermal heating and also retains part of the generated hydrocarbons, which might lead to erroneous kerogen typing when using thermal methods. The most immature samples are characterised by relatively higher proportion of oxygen-bearing functional groups which are more labile bonded to the kerogen and are released at lower temperatures during pyrolysis. Temperatures of initiation of kerogen cracking have shown to be more sensitive to reflect the maturity than temperatures of maximum rate of hydrocarbons release under the low heating rates used in this study. The most aliphatic and oxygen-rich kerogen have shown to yield the highest conversion to shale oil whereas the initially most aromatic kerogens are more prone to condense yielding higher coke amounts.
Oil Shale, 2008
In this research, thermal characteristics and kinetic parameters of Tarfaya oil shale and its kerogen samples were determined by thermogravimetry (TG/DTG) under non-isothermal heating conditions. The pyrolysis experiments were performed increasing the temperature up to 1273 K at heating rates of 2, 10, 20 and 50 K/min in an inert atmosphere of nitrogen. The mass loss curve showed that pyrolysis of kerogen took place mainly in the range of 433-873 K. At higher temperatures there was a significant mass loss due to decomposition of mineral matter. It has been found that for oil shale and its kerogen analysed using the TG/DTG, the increase in the heating rate shifts the maximum rate loss to a higher temperature. Kissinger-Akahira-Sunose, Friedman, Flynn-Wall-Ozawa and Coats-Redfern methods were used to determine the apparent activation energies of materials' degradation. The analyses of the process mechanism by the methods of Criado et al. and Coats-Redfern showed that the most probable model for the pyrolysis process of organic matter of oil shale agrees with the diffusion model (D4 mechanism), and the thermal degradation process of isolated kerogen corresponds to a mechanism involving a simple norder model (F1 mechanism). The apparent activation energies for the organic matter of oil shale and isolated kerogen were 80-87 and 69-76 kJ/mol, respectively. A single kinetic expression is valid over the temperature range of kerogen pyrolysis between 433 and 873 K. In addition, the results indicate that the removal of mineral matter affected the kinetics and mechanism established for kerogen in oil shale.
Characterisation of some Australian oil shale using thermal, X-ray and IR techniques
Fuel, 2005
Oil shales and coal have considerable amount of pyrite which undergoes various thermal transformations during their processing or combustion. Reactions and changes in pyrite chemistry vary considerably under different environmental conditions. In this paper, we report an in situ high-temperature X-ray diffraction study of phase transformations in pyrite under variable environmental conditions (atmospheric pressure (1 atm.), low air pressure (<0.001 atm.), inert and carbon dioxide atmosphere). We observe that while heating of pyrite in air promotes the formation of hematite (a-Fe 2 O 3 ), magnetite (Fe 3 O 4 ) is a major product in low pressure environment. On the other hand, in the inert environments (nitrogen and argon) pyrrhotite, a non-stoichiometric iron sulphide, is the most dominant product. However, in carbon dioxide (CO 2 ) environment, pyrrhotite is an intermediate low temperature product which further transforms into magnetite and hematite, attributed to the dissociation of the CO 2 into O 2 and CO providing conducive conditions for the oxidation. We also propose the possible reaction pathways including self-dissociation of CO 2 .
AAPG Bulletin, 2012
Evaluations of porosity relevant to hydrocarbon storage capacity in kerogen-rich mudrocks (i.e., source rocks) have thus far been plagued with ambiguity, in large part because conventional core and petrophysical techniques were not designed for this rock type. The growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity. This mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts (except perhaps chemically) with previously assumed "matrix" or "mineral" porosity that is dominated by bound water, and that may be largely irrelevant to hydrocarbon storage capacity in these rocks. To address this newly recognized and important nonmatrix kerogen pore system, that is arguably the dominant hydrocarbon storage and mobility network in these rocks, we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation. Kerogen porosity development is estimated within the upper Albian Mowry Shale in the Powder River Basin of Wyoming to illustrate the approach. Relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis, where we estimate that kerogen porosity does not typically exceed 3% of bulk rock volume.
Energy & Fuels, 1995
The artificial maturation of Woodford Shale has been performed using confined pyrolysis, hydrous pyrolysis, and high-pressure hydrous pyrolysis in order to test the effects of pressure and the presence of water on the thermal evolution of a type I1 kerogen. Despite the fact that identical time-temperature-pressure conditions were used in both pyrolysis systems (260-400 "C, 72 h duration, 250-1300 bar pressure), the results are very different. This study focuses on the fate of the residual kerogen during maturation in both pyrolysis systems. During hydrous pyrolysis, high pressure induces a strong suppression effect on kerogen thermal breakdown that is far lower during confined pyrolysis (hydrocarbons + gaseous effluents pressure). In addition, hydrous pyrolysis conditions induce a retardation in kerogen thermal breakdown and strongly inhibit aromatization of the residual kerogen; maturation occurs faster in confined conditions and aromatization is prevalent. The very different behavior of the residual kerogen with different pyrolysis media implies that different hydrogen sources and hydrogen exchange mechanisms are involved during the maturation process. The availability of water and the confinement of the system lead to a competition between water and the residual kerogen (+ polars) as major sources of hydrogen. Depending on the dominant hydrogen source, the kerogen responds differently to the heating process and the pressure effect. These considerations lead to the conclusion that it is important to better constrain the physicochemical conditions occurring in source rocks in order to properly extrapolate the artificial maturation results to the geological context.