Optical Analysis of Pyrolysis Products of Green River Oil Shale

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Optical Analysis of Pyrolysis Products of Green River Oil Shale Kyle D Bake, and Andrew E Pomerantz Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01020 • Publication Date (Web): 24 Oct 2017 Downloaded from http://pubs.acs.org on October 25, 2017

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Optical Analysis of Pyrolysis Products of Green River Oil Shale

Kyle D. Bake and Andrew E. Pomerantz Schlumberger-Doll Research, Cambridge, Massachusetts 02139, United States

Abstract: The chemical composition of hydrocarbon fractions of artificially matured (pyrolyzed) Green River oil shale were studied by optical spectroscopy (VIS-NIR). The shale samples were pyrolyzed to several maturities, allowing the compositions of the hydrocarbon fractions to be analyzed as a function of maturity. Oil (the hydrocarbon fraction volatile at pyrolysis conditions but liquid at room temperature), bitumen (the hydrocarbon fraction nonvolatile at pyrolysis conditions and soluble in organic solvent), and asphaltene (the fraction of bitumen that is insoluble in heptane), were all found to show an exponential increase in optical absorption with increasing optical frequency. A similar exponential increase has been observed in other hydrocarbon mixtures and is described by the Urbach Tail formulation. The optical properties of the oil are found not to change with maturity, likely because oil is released by volatilization throughout the maturation process, thus producing a distilled product. Bitumen and asphaltenes, however, show strong trends with maturity, including the formation of larger chromophores during maturation. This result differs from naturally occurring crude oils and asphaltenes which show remarkably similar Urbach Tail slopes over a large range of API gravity. This difference between the naturally occurring and laboratory produced products can be explained as result of the laboratory produced bitumen and asphaltenes being retained in the source rock during semi-open pyrolysis while natural oils are expelled.

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Introduction Oil shales are sedimentary rocks containing significant quantities of insoluble organic material, known as kerogen, which under high temperature can be pyrolyzed to form petroleum. These shales are of interest to the petroleum industry for two reasons. First, the energy contained in them can be significant, such that large quantities of petroleum may be produced by pyrolyzing the rock. A primarily example of the significance of this resource is the Green River oil shale formation in the western US, with a resource size of the equivalent of approximately 1.44 trillion barrels of oil, more than the world’s previous historical total oil consumption.[1] Similar oils shales have been produced by pyrolysis in various locations starting in the middle of the mid 19th century. [2-21] Second, oil shales are also model systems for studying high maturity source rocks that contain liquid petroleum, such as many of the tight oil plays currently produced by hydraulic fracturing rather than pyrolysis. The reservoir quality and completion quality of those plays depend on maturity, but isolating the effects of maturity on the rock properties using naturally occurring samples is challenging because samples with significant differences in maturity often vary in other properties as well. Oil shales can be pyrolyzed in a lab setting to monitor structural changes in the rock properties due solely to variations in maturity.[22] Pyrolysis is a complex process involving the conversion between different phases of organic matter. Initially, the dominant organic phase in oil shale is kerogen, which is solid and defined as being insoluble in any common organic solvent.[23] In pyrolysis, that kerogen converts into other organic phases: gas, which is volatile at both pyrolysis and room temperature; oil, which is volatile at pyrolysis temperature but condenses at room temperature; and bitumen, which is nonvolatile at pyrolysis temperature but soluble in organic solvent.[24] Often, a dominant mechanism is a multistep process in which kerogen first converts to bitumen which then further converts into oil and gas plus an insoluble solid material (which is indistinguishable from kerogen by any laboratory separation but is occasionally called pyrobitumen, char, or coke to describe the mechanism of its formation). [24-31] Another mechanism is the direct formation of oil and gas from kerogen breakdown. The severity of this pyrolysis— incorporating both the temperature the rock was exposed to and the duration of the exposure—is known as maturity and can be computed given a time-temperature history.[32] The mechanism of pyrolysis has been studied extensively, particularly the kinetics of the pyrolysis process [33, 34] and the influence of pyrolysis on the composition of the organic phases [35-38]. Kinetic models describe the generation of oil as a series of thermal reactions, and kinetic parameters describing the reaction rates have been determined. The composition of the oil and gas phases have been measured by gas chromatographic techniques, with the observation that the composition of the gas is nearly independent of maturity while the quantity of gas increases with maturity.[25, 39] The kerogen and bitumen phases have been analyzed by various spectroscopic techniques including NMR and IR, with the observation that the composition of both phases change significantly with maturity. [24, 40] The composition of asphaltenes has been found to evolve with maturity, with major compositional changes including the loss of heteroatoms at low maturities and increasing aromaticity of carbon structures at high maturities. [38]


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Optical spectroscopy has been a popular method for analysis of crude oils for many years. A significant advantage of optical spectroscopy is the ability to perform the measurement not only under laboratory conditions but also downhole, using spectrometers that operate in oil wells at high temperature and high pressure.[41] The ability to measure optical spectra downhole enables the use of the technique to identify compositional gradients in crude oil [42-44] measuring the variation in oil composition for different vertical and lateral locations in the reservoir. These compositional gradients are used to assess reservoir architecture, such as connectivity, and are enabled by recent advances such as the FloryHuggins-Zuo equation of state[45, 46] that models compositional gradients in the asphaltene fraction based on the Yen-Mullins model[47-49] of asphaltene molecular and nanoaggregate structure. Optical spectroscopy probes electronic transitions between occupied and unoccupied molecular orbitals. In crude oils, these transitions occur mostly in fused aromatic rings of varying sizes. The location in the energy spectrum of these transitions is dependent on the size of the aromatic ring structure. The areas of a molecule which absorb light is known as the chromophore. Large aromatic ring structures will absorb at lower energy than do smaller chromophores, as described by the quantum particle-in-a-box principle.[50] Optical spectra of crude oils are often described by the Urbach tail phenomenology[51-53], which was initially applied to semiconductors [52]. The Urbach tail model describes an exponential decay of absorption with increasing photon wavelength. For semiconductors, the Urbach tail describes the thermal excitation of optical absorber sites. In hydrocarbon mixtures, however, the Urbach tail behavior is due to the overlapping electronic transitions of different polyaromatic compounds. Thus the Urbach tail is used to describe the composition of the mixture, in particular the abundance of fused ring systems of different sizes. Crude oils of widely varying API gravity are found to exhibit similar Urbach tails, reflecting similar distributions in aromatic ring structures.[51, 53] Here we describe the application of optical spectroscopy to various hydrocarbon phases produced during pyrolysis of Green River oil shale. Oil, bitumen, and asphaltene fractions each formed at a range of maturities are analyzed separately. Optical spectra of each fraction at each maturity are found to follow closely the Urbach tail model. Similar to natural crude oils, the slope of the Urbach tails in the pyrolysis oils are found to be essentially independent of maturity. The bitumen and asphaltene Urbach tails, however, show a marked dependence on maturity. Experimental: Sample Description Shale samples and pyrolysis conditions used here have been described elsewhere. [25] Briefly, Green River oil shale comprises fine-grained lacustrine sediments deposited in Lake Uinta across much of the Piceance and Uinta Basins between approximately 55 and 45 Ma [54]. Rock samples were collected from Rio Blanco County, Colorado (Piceance Basin) as cuttings from the Garden Gulch Member of the Green River Formation, at a depth between 2012 and 2088 ft. within the illite-rich R-1 zone. The shale is rich in organic matter, with an initial total organic carbon (TOC) content of 14%, and contains type I kerogen. The cuttings were recovered by reverse circulation drilling in water, and room dried cuttings were used as received. Cuttings were homogenized, split and crushed to less than 100 micrometers as described by


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Le Doan et al.[25]. The starting composition of the oil shale used for each pyrolysis experiment was essentially identical as confirmed by geochemical and mineralogical analysis. [25] The shale, with a starting maturity of 0.48 RO, was pyrolyzed under semi-open conditions in a homebuilt system (figure 1) patterned after work by Burnham and Singleton [55], in which the volatile products of pyrolysis escape the reactor as they are generated while the pressure in the pyrolysis cell is held constant. These conditions approximate those occurring in in-situ oil shale retorts. This vaporization as a means of transport of products in the semi-open pyrolysis is thus different than transport in natural petroleum formation where buoyancy is a major mechanism of separation. Organic molecules that are released from the cell because they are volatile at pyrolysis temperatures but then condense at room temperature are defined as oil. Organic molecules that remain in the pyrolysis cell but can later be dissolved using Soxhlet extraction with 9:1 dichloromethane:methanol are defined as bitumen. The distinction between bitumen and oil includes both mass transport and chemical composition influences. Because they are non-volatile, asphaltenes are primarily present in the bitumen phase rather than the oil phase. In order to isolate the asphaltenes from the bitumens, bitumen was stirred overnight in heptane in a 40:1 ratio. The bitumen-heptane solution was filtered and the collected asphaltenes were further purified by washing with heptane in a Soxhlet extractor. Aliquots of shale were heated at various rates, final temperatures, amounts of time, and pressures, resulting in a range of thermal maturities. The thermal maturity following each pyrolysis experiment was computed from the established ‘EASY%Ro’ relationship.[32] EASY%Ro estimates the thermal maturity based the thermal history and is expressed in units comparable to those measured in vitrinite reflectance experiments. Figure 2 shows the measured relative amount of gas, oil, bitumen, and asphaltenes produced for each maturity level reached during pyrolysis. In these experiments, bitumen acts partially as an intermediate, being produced at low maturities and consumed at higher maturities. Kerogen (defined here as all insoluble organic matter) is predominately consumed at low maturity but can be formed at higher maturity by bitumen coking. Oil and gas are produced primarily at high maturity by bitumen decomposition. Optics Measurements Visible-NIR spectra were obtained using a CARY 5000 UV-Vis-NIR spectrometer. Samples were placed in a 50 micron path length cuvette. Asphaltene and bitumen samples were dissolved in toluene and carbon tetrachloride, respectively, for spectroscopic measurements. These solutions were made at 1 mg/ml concentration. Oil samples were run neat. Spectral were collected over the range 500 – 2,500 nm (4,000 – 20,000 cm-1). Background signal was collected as pure solvent (for bitumen and asphaltene samples) or air (for oil samples) and subtracted. The spectra were then normalized to compensate for dilution. Results : The UV-Vis spectra for the oil, bitumen, and asphaltene fractions from figure 2 are shown in figure 3. Spectra are plotted as the log of the optical density (OD) vs linear optical frequency (wavenumber). The high wavenumber region of each spectra shows an exponential increase in absorption with increase in


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wavenumber (appearing as linear in the semi-log plots in Figure 3). This increase has been observed previously and described according to the Urbach formalism [52]. The Urbach formalism describes absorption over a broad frequency range according to the following relationship with two adjustable parameters = exp

ℎ

Where α is the extinction coefficient (proportional to optical density) at frequency ω, ℎ is Plank’s constant, and the two adjustable parameters are the reference extinction coefficient (α0) and the Urbach decay constant (Eo). The Urbach formalism has been applied to explain optical absorption spectra in diverse materials such as semiconductors and petroleum. In semiconductors [52], absorbance at difference frequency results from selective excitation from initial states with different energies which are populated thermally. As a result, for semiconductors E0 is approximately equal to kT.[56] For complex mixtures such as petroleum, the thermal effect is small compared to the effect of different transition energies found in different components of the mixture, and E0 is typically an order of magnitude greater than kT. [53] Therefore, the slope of the Urbach tail can be used to estimate the relative abundance of different components with different transition energies. In particular, optical absorption in organic mixtures such as petroleum results from excitation of polycyclic aromatic ring systems. Larger ring systems (i.e. containing more fused aromatic rings) absorb at longer wavelength (shorter wavenumbers) than smaller rings systems, in accordance with the quantum mechanical particle in a box model, so the slope of the Urbach tail in petroleum reflects the distribution of polycyclic aromatic ring sizes: steeper slopes (small Eo) indicate significantly greater abundance of small rings systems compared to larger rings systems, while flatter slopes (large Eo) indicate more similar abundances of small and large ring systems. Spectra were fitted to the Urbach model (an example of the fitting is shown in figure 4), plus an additional offset to correct for scattering. Figure 3 plots spectra, the α0, and the E0 derived from the fitting. [57] We believe that the largest error in α0 is from the gravimetric analysis of the measured samples – which would result in an error of +/- 10% of the value. For the extinction coefficient, the fitting of the Urbach decay formulism is the highest source of error. From sensitivity analysis, this fit error is less than +/- 5%. The second row of Figure 3 plots the extinction coefficient with respect to maturity. Extinction coefficients of the oil are low and show little change with maturity, while bitumen and asphaltene have much higher extinction coefficients and show a trend with maturity. The third row of Figure 3 plots the Urbach decay constant, Eo, versus maturity. Eo has units of energy and is expressed here in multiples of kT (where T is 273 K). [41] The bitumen and the asphaltene fractions show an increase in the E0 as maturity increases, while the oil’s E0 remains low and constant. Discussion Oil Oil is defined here as the fraction of the organic matter that is volatile at pyrolysis conditions but condenses at room temperature and atmospheric pressure. The spectra of these pyrolysis oils obey the


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Urbach formulism, as has been observed for natural oils of widely varying API gravity.[53] Natural oils of widely varying API gravity all have similar Eo (~10 kT). The values of Eo observed here are similar to one another, but much lower than those observed in natural systems (~1 kT). The Eo does not depend on maturity because the volatilization processes extracts a nearly constant volatility range in each of the pyrolysis experiments. Unlike natural oils which are expelled from the source rock primarily by buoyancy, the pyrolysis oils are expelled by volatilization. Thus, the pyrolysis oil is essentially a distilled product. Large fused ring systems in petroleum generally are not volatile, so they partition primarily into the bitumen phase rather than the oil phase in the pyrolysis experiments. The pyrolysis oils have relatively high concentrations of small ring systems compared to large ring systems and therefore have low α0. Consistently, these oils show little variation in composition with maturity as measured by techniques such as two-dimensional gas chromatography (GCxGC), thin layer chromatography, and gel permeation chromatography (GPC). [25] Bitumen Bitumen is defined here as the fraction of the organic matter that is nonvolatile at pyrolysis conditions and soluble in organic solvent. As with the oils, the spectra of bitumen obey the Urbach formalism. However, the α0 of the bitumen is approximately three orders of magnitude greater than the α0 of the oil. This strong difference is due to the fact that the larger chromophores, including asphaltenes, are non-volatile at pyrolysis conditions and therefore found primarily in the bitumen phase. The bitumen spectra show pronounced trends with maturity, as both the α0 and the E0 increase with maturity. Consistently, large variations with maturity have been found in other properties of these bitumen. [24, 25, 40] For example, X-ray absorption near edge structure (XANES) studies showed that the sulfur speciation changes with maturity, specifically the thiophene abundance increases with maturity while the sulfoxide abundance decreases. NMR studies have shown that the aromatic:alipahatic carbon ratio increases with maturity which agrees with elemental analysis that showed the hydrogen:carbon ratio decreases with maturity. Studies by infrared spectroscopy show that the chain length increases with a corresponding decrease in oxygen content with maturity. The variation of E0 with maturity is unlike what is found in oils produced here nor what is found in naturally produced oils. In natural oils, E0 is consistently near 10 kT, even for oils of widely varying API gravity. [51] Here, the E0 of the native state bitumen (EASY%RO = 0.48%, not pyrolyzed in the laboratory) is 13 kT, as may be expected because this bitumen was not generated in the laboratory but instead was generated by a modest amount of natural maturation. For bitumens generated by laboratory pyrolysis, E0 increases with maturity up to 25 kT. This increase in E0 demonstrates that, as maturity increases, the composition of the bitumen also changes to favor larger, fused ring systems. Asphaltenes Optical absorption in conventional oils is typically dominated by the asphaltene fraction, such that the optical density of oils in the visible and near-IR regions are generally proportional to the asphaltene content of the oil. [58, 59] Thus, the similarity in Eo of natural oils of a wide range of API gravities [60] implies a similarity in optical properties of asphaltenes from this wide range of fluids. Moreover,


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asphaltenes collected from various conventional reservoirs worldwide show relatively little variation in several properties such as molecular weight [61], molecular architecture [62], colloidal properties [63], density [64], and solubility parameter [64], although a range of H/C ratios has been observed [65]. Additionally, asphaltenes from a single reservoir with a 10x variation in asphaltene content driven by gravitational segregation showed essentially no variation in composition, including sulfur speciation, molecular weight, and aggregate weight. [66-68] In contrast, the asphaltenes produced during these pyrolysis experiments have been analyzed separately and found to change dramatically in composition during maturation. In particular, increasing maturation results in sulfur chemistry shifting from oxidized to reduced, an increase in the molecular weight, and an increase in the aromaticity. [38] It is found here that their optical properties also vary greatly over this maturity range. For example, the asphaltene α0 is found to increase by a two orders of magnitude while the asphaltene E0 is found to increase by a factor of two, from 13 to 25 kT. The increase in asphaltene E0 with maturity suggests that larger aromatic structures are formed in asphaltenes with increasing maturity, because E0 increases with greater abundance of large aromatic ring systems compared to small ring systems. This result is consistent with the previous measurements that shows the asphaltenes increase in both molecular weight and aromaticity with maturity. [38] The observed increase in α0 with maturity is again consistent with an increase in ring size with maturity, because larger aromatic systems typically have greater optical extinction coefficients than small ring systems in this spectral range. [57] The optical properties of the isolated asphaltenes can also be used to understand the optical properties of the bitumens described above. In general, the α0 of a mixture such as bitumen or oil depends on the concentration and the extinction coefficient of the chromophores in the mixture. In naturally occurring oils, the dominant chromophore is the asphaltene fraction, and the extinction coefficient of asphaltenes of oils in the same field is sufficiently similar that the α0 of the oil can be taken as proportional to the asphaltene content of the oil. For these pyrolysis asphaltenes, their extinction coefficient varies by a factor of 100, as a result of the increasing ring size with maturation. At the same time, the asphaltene contents of the bitumens also varies. Despite this variation in asphaltene content and asphaltene extinction coefficient, the optical absorption of the bitumens is still dominated by the asphaltene fraction: Figure 5 shows a reasonably tight correlation between the measured bitumen OD and that predicted by assuming all of the bitumen optical absorption is attributed to the asphaltene fraction (obtained by multiplying the asphaltene content of the bitumen by the OD of the asphaltenes). Moreover, the E0 of the asphaltene fraction is consistently only slightly higher than that of the corresponding bitumen fraction at all maturities (fig 6). If the bitumen optical absorption resulted entirely from the asphaltene fraction, then the E0 of the bitumens and the corresponding asphaltenes would have to be identical. The small increase in E0 for the bitumen phase results from the presence of small rings systems, that are soluble in heptane, in bitumen that are not contained in the asphaltene fraction but contribute slightly to the optical absorption, as an increase in the abundance of small ring systems causes Eo to decrease. The variation in the bitumen and asphaltene fractions may be unexpected given the consistency in EO for crude oils of varying API gravity. This difference in composition could be attributed to three differences


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between the generation processes in natural maturation versus artificial maturation. First, these pyrolysis bitumens and asphaltenes are generated by nearly anhydrous pyrolysis at high temperatures for short durations, while natural oils are typically produced in the presence of liquid water at relatively low temperature and long times. These two factors could skew the reaction pathways to those with higher activation energies or, due to the lack of water, to products with different chemical make-up. Second, these pyrolysis fractions studied here are retained in the hot source rock throughout maturation, while natural oils are expelled from the source rock. As a result, these fractions were subjected to more severe secondary cracking than natural oils. This explanation is consistent with the observation that the kerogen phase from this same set of pyrolysis experiments, which also remain in the heated zone throughout maturation, also increases in E0 with increasing maturity. [57] Third, because theses pyrolysis fractions were extracted by solvent rather than expelled by buoyancy, they will contain molecules that are sorbed to the kerogen and therefore would not be present in expelled reservoir oils.

Conclusions: In this study, optical spectroscopy was used to study the oil, bitumen, and asphaltene fractions from laboratory semi-open pyrolysis using Green River shale from the R1 zone. The sample was pyrolyzed to a range of maturities, and optical spectroscopy was used to measure the composition of each fraction as a function of maturity. All of these fractions obey Urbach tail behavior, analogous to crude oil samples obtained from naturally occurring reservoirs. However, while all naturally formed oils, over a wide range of API gravity, demonstrate a consistent E0 of ~10 kT, some of the fractions studied here show a stark change in E0 with maturity. The pyrolysis oil samples are very low in color and show no trend with maturity, with all of the oils possessing similar E0 near 1 kT. These oil samples were collected during the pyrolysis experiments as molecules that are volatile at pyrolysis conditions and condense at room temperature. As a result, the concentration of asphaltenes in oil is low, consistent with the low color of the oil. Additionally, because the oil is a distillate, it may be expected to show little change with maturity. The relatively constant composition of the oil phase over a wide range of maturity is consistent with previous measurements of oil composition performed using techniques such as using XANES, GCxGC, and GCP. [25] The bitumen, however, is strongly colored and shows an increase of both the α0 and the E0 with increasing maturity. The deep color is consistent with the majority of the asphaltenes being present in the bitumen phase. The native state (not pyrolyzed in the laboratory) bitumen sample has an E0 of 13 kT, similar to other naturally occurring crudes. As maturity increases, the E0 increases by a factor of two and the α0 increases by two orders of magnitude, both suggesting an increase in the concentration of large aromatic ring systems with maturity. This variation is not observed in natural oils, which show relative consistency in E0 even over a large range in API gravity. The difference in composition between the pyrolysis bitumen and naturally-occurring oils may reflect differences between the mechanisms of bitumen formation in the laboratory and petroleum generation/expulsion in nature. There are three


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major differences in the mechanisms: first, the laboratory produced samples are generated by semiopen pyrolysis at high temperatures for short durations in the absence of liquid water, while natural oils are produced in the presence of liquid water at relatively low temperatures and long times; second, the bitumens studied here are retained in the hot source rock throughout maturation, while natural oils are expelled from the source rock, so these bitumens were subjected to more severe secondary cracking than occurs for natural oils; third, the bitumens studied here were extracted by solvent and thus may include components that would be retain by sorption in natural source rocks where the expulsion is driven by buoyancy. [38] The trends on the optical properties of the asphaltene fraction as the same as those in the optical properties of the full bitumen, because the optical absorption of the bitumen is dominated by the asphaltene fraction. There is a slight increase in E0 of bitumen compared to the corresponding asphaltene, which is attributed to the presence of small ring systems in the bitumen that are not captured in the asphaltene fraction. The conclusion that the asphaltenes contain larger ring systems at greater maturity is supported by previous measurements showing an increase in both molecular weight and aromaticity with maturation. [38] In natural systems, the oil, with dissolved asphaltene, are expelled from the source rock by buoyancy throughout maturation and, as a result, contain fewer high maturity asphaltenes than the asphaltenes studied here. In experiments presented here, the asphaltenes remain in the reactor through-out pyrolysis and thus mature further, more similar to unconventional resources where the source and the reservoir are in the same location and the asphaltenes have thus not migrated.


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Figures:

Figure 1: Pyrolysis laboratory schematic: (1) needle valve, (2) piston valve, (3) solenoid value, (4) liquids collector, (5) four-way valve, (6) shut-off valves, (7) sample tubes, (8) three-way valve, (9) gas bag, (10) liquid level measurement.[25]


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100% 90% 80% 70% 60%

Gas

50%

Oil

40%

Asphaltene

30%

Bitumen

20%

Kerogen+Coke

10% 0% 0.48

0.78

0.83

0.95

1.19

1.28

Easy%Ro

Figure 2: Mass fraction of each organic carbon phase for pyrolysis experiments.


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Figure 3: Optical spectra, absorption, and slope of Urbach tail for oils, bitumen, and asphaltenes (normalized).

250 Obtained Spectra 200 Urbach Formulism Fit 150

OD

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100

50

0 0

5000

10000

15000

Wavenumber

(cm-1)

20000


25000

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Figure 4: Comparison of obtained spectra and Urbach formulism fit. The Urbach Formulism was fit to = exp #

$% (. &'

50 45 40

Calculated Bitumen OD

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35 30 25 20 15 10 5 0 0

10

20

30

40

50

Actual Bitumen OD

Figure 5: Calculated bitumen OD using asphaltene OD and % asphaltene from wet chemistry versus measured bitumen OD.


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35

30

25

E0 (kT) of Asphaltene

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20

15

10

5

0 0

5

10

15

20

25

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E0 (kT) of Bitumen

Fig 6: Cross-plot of E0 for asphaltene and bitumen. At a given maturity, the E0 of asphaltenes is slightly higher than the E0 of the corresponding bitumen


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References: 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

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Optical Analysis of Pyrolysis Products of Green River Oil Shale

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