Shale Mineralogy Research Articles

Modeling of gas generation from the Barnett Shale, Fort Worth Basin, Texas

The generative gas potential of the Mississippian Barnett Shale in the Fort Worth Basin, Texas, was quantitatively evaluated by sealed gold-tube pyrolysis. Kinetic parameters for gas generation and vitrinite reflectance (Ro) changes were calculated from pyrolysis data and the results used to estimate the amount of gas generated from the Barnett Shale at geologic heating rates. Using derived kinetics for Ro evolution and gas generation, quantities of hydrocarbon gas generated at Ro 1.1% are about 230 L/t (7.4 scf/t) and increase to more that 5800 L/t (186 scf/t) at Ro 2.0% for a sample with an initial total organic carbon content of 5.5% and Ro = 0.44%. The volume of shale gas generated will depend on the organic richness, thickness, and thermal maturity of the shale and also the amount of petroleum that is retained in the shale during migration. Gas that is reservoired in shales appears to be generated from the cracking of kerogen and petroleum that is retained in shales, and that cracking of the retained petroleum starts by Ro 1.1%. This result suggests that the cracking of petroleum retained in source rocks occurs at rates that are faster than what is predicted for conventional siliciclastic and carbonate reservoirs, and that contact of retained petroleum with kerogen and shale mineralogy may be a critical factor in shale-gas generation. Shale-gas systems, together with overburden, can be considered complete petroleum systems, although the processes of petroleum migration, accumulation, and trap formation are different from what is defined for conventional petroleum systems.

Characterization of sulfide deposits by airborne magnetic and gamma-ray responses in eastern Finland

Integrated interpretation of aerogeophysical data permits geophysical characterization of sulfide deposits in eastern Finland. The structural control and the hydrothermal alteration of the rocks can be discerned from airborne magnetic and radiometric data. The Cu–Co–Zn deposits associated with serpentinite–dolomite–calc-silicate rock–siliceous rock–black shale settings of the Outokumpu type are locally characterized by reduced intensity of magnetization and electrical conductivity and reduced eTh and K radiation. Enhanced eU/eTh anomalies are commonly spatially related to major structural lineaments, such as the boundaries of structurally more coherent bedrock blocks or intersections of faults and shear zones. Electromagnetic surveys can be used to distinguish black shales and serpentinites in the region. The sulfide deposits in eastern Finland can be divided into two groups on the basis of airborne geophysical characteristics: (1) intense magnetization and high electrical conductivity and (2) moderate magnetization and electrical conductivity. In the sulfide deposits of group 1, ore-forming constituents mainly precipitated during primary sedimentation (for example, the black-shale-hosted Ni–Cu–Zn ore at Talvivaara). Group 2 is related to sulfide deposits where major ore-forming processes have affected the associated black shale formation after the sedimentation phase (Outokumpu-type Cu–Co–Zn deposits). In cases where the magnetization and electrical conductivity of black shales are especially weak, ore formation processes probably continued during late metamorphic or post-metamorphic deformation. The theoretical basis for the observed differences in magnetic response between different deposits has to do with the mineralogy of the black shales. Pyrite changes into ferrimagnetic monoclinic pyrrhotite during metamorphism above greenschist facies, especially along tectonic structures. If no further alteration occurs, pyrrhotite-bearing black shale formations appear as highly magnetic and electrically conductive zones on geophysical maps. Wherever intense tectonic deformation, emplacement of quartz–sulfide veins, hydrothermal alteration, or contact metamorphism has affected the black shale formation after sedimentation, both magnetic and electromagnetic responses may be weakened because of diminished amounts of the pyrrhotite-bearing and graphite-rich material. In addition, the presence of antiferromagnetic pyrrhotite of hexagonal crystal structure may decrease the magnetic response. The classification presented here applies specifically to eastern Finland, but may be widely applicable to terranes with abundant black shale formations that have undergone regional metamorphism of upper greenschist facies or higher. Association of sulfide ores with black shales is a common feature in the geological record. Our integrated geophysical method offers a quick way of examining large areas, and it should prove useful in the search for sulfide deposits in other parts of the world.

Contact metamorphism of Palaeozoic shale in southern Sweden: influences on clay mineralogy and implications for railway construction material properties

Abundant shale fragments were observed in dolerite material used for railway construction in western Skåne, due to quarrying of Permo-Carboniferous dolerite in contact with Silurian shale (the Colonus Shale) in the Rönnarp Quarry, western Skåne. Shale fragments were particularly enriched in the finest fractions of the crushed rock material. We analysed the clay mineralogy of shale from the railway material and at different distances from the dolerite in the quarry, in order to better understand the properties of the delivered rock material. The illite and chlorite dominated Colonus Shale in Skåne typically shows background illite crystallinity in the uppermost diagenetic realm. In the Rönnarp Quarry, fissile shale a few meters away from the dolerite intrusion shows illite crystallinity in the anchimetamorphic stage. In massive shale less than 1 m from the shale-dolerite contact, swelling clay minerals have formed at the expense of illite. Therefore, despite the massive appearance of the contact metamorphosed shale, it is suggested that such rocks should be avoided during construction material production. A tentative model for post-intrusion hydrothermal clay mineral transformation is suggested.

Chlorite composition and geothermometry: a comparative HRTEM/AEM-EMPA-XRD study of Cambrian basic lavas from the Ossa Morena Zone, SW Spain

AbstractChlorites from Cambrian basaltic vesicular lavas, characterized by relatively highXc (0.81-0.98), gave temperatures of formation of 285 to 350°C (Cathelineau's empirical geothermometer). Both theXcand temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy. The HRTEM and XRD studies indicate the absence of smectite layers in these chlorites; i.e. according to lattice images, the actual value ofXcis 1. The chlorite composition in these basaltic lavas must, therefore, be explained in relation to their whole-rock geochemistry, with which a good correlation has been found. The basaltic lavas are characterized by relatively high FeO/M ratios (3.28±1.66) and must be considered as an Fe-rich system, with similar chemical behaviour to pelitic rocks. In these cases, direct chlorite formation, without a previous smectite precursor, is a normal occurrence and theXccalculation and empirical geothermometric calculations are inadequate.

DETECTING OVERPRESSURE USING POROSITY-BASED TECHNIQUES IN THE CARNARVON BASIN, AUSTRALIA

Overpressure has been encountered in many wells drilled in the Carnarvon Basin. Sonic logs are used to estimate pore pressure in shales in the Carnarvon Basin using the Eaton and equivalent depth methods of estimating pore pressure from velocity data with reference to a normal compaction trend. The crux of pore pressure estimation from the sonic log lies in the determination of the normal compaction trend, i.e. the acoustic travel time (Δt)/depth (z) trend for normally pressured sediments. The normal compaction trend for shales in the Carnarvon Basin was established by fitting an Athy-type exponential relationship to edited sonic log data, and is: Δt = 225 + 391exp(-0.00103z) Vertical stress estimates are also needed for the Eaton and equivalent depth methods used herein. A vertical stress (σv) relationship was obtained by fitting a regression line to vertical stress estimates from the density log, and is: σv = 0.0131 z1.0642 The Eaton and equivalent depth methods yield similar pressure estimates. However, the equivalent depth method can only be applied over a limited range of acoustic travel times, a limitation that does not apply to the Eaton method. The pressure estimates from the Eaton method were compared to pressures measured by direct pressure tests in adjacent permeable units. There is a good correlation between Eaton and test pressures in normally pressured intervals in three wells and overpressured intervals in two wells. Eaton pressure estimates underestimate overpressured direct pressure measurements in four wells by up to 13 MPa. This is consistent with overpressure being generated (at least in part) by a fluid expansion mechanism or lateral transfer of overpressure. The Eaton pressures in one well are, on average, 11 MPa lower than hydrostatic pore pressure recorded in direct pressure measurements below the Muderong Shale. The sediments in this well appear to be overcompacted due to exhumation. Mud weights can be used as a proxy for pore pressure in shales where direct pressure measurements are not available in the adjacent sandstones. The Eaton pressure estimates are consistent with mud weight in the Gearle Siltstone and Muderong Shale in 4 of the 8 wells studied. The Eaton pressures are on average 10 Mpa in excess of mud weight in the Muderong Shale and Gearle Siltstone in three wells. It is unclear whether the predicted Eaton pressures in these three wells accurately reflect pore pressure (i.e. the mud weights do not accurately reflect pore pressure), or whether they are influenced by changes in shale mineralogy (because the gamma ray filter does not differentiate between shale mineralogy).

Frio Shale Mineralogy and the Stoichiometry of the Smectite-to-Illite Reaction: The Most Important Reaction in Clastic Sedimentary Diagenesis

AbstractBurial diagenesis of shales of the Frio Formation resulted in an increase in the abundance of mixed-layer illite-smectite (I-S), albite and chlorite, and a decrease in the abundance of K-feldspar, illite and kaolinite. Some of the mineralogic trends determined in this study contrast with the results of Hower et al. (1976) and other studies of Frio shales. The differences are due to improvements in laboratory and clay quantification techniques since the time of the earlier research. I-S composition changed from ~20% to ≥80% illite, and mineralogic and chemical reaction of I-S continued throughout burial. Shale diagenesis was an open-system process that required addition of K2O and A12O3, and resulted in loss of SiO2. The amount of SiO2 made available by shale diagenesis is sufficient to be the source of the quartz-overgrowth cements in the associated Frio sandstones. The relationships between I-S diagenesis and fluid flow from shales into sandstones, generation of abnormal formation-water fluid pressure, onset of sandstone diagenesis and distribution of authigenic phases in sandstones indicate that reaction of the I-S in shales is one of the most important components of the sandstone/shale/formation water diagenetic system.

Comparison of the Mineralogical and Chemical Composition of 2 Shales from the Western Canada Sedimentary Basin and the United States Gulf Coast

AbstractThe mineralogy and geochemistry of shales reflect the composition of the initially deposited precursor mud, subsequently modified by diagenetic processes. To see if significant geochemical differences exist between shales that mainly owe their present-day composition to either deposition or diagenesis, we compare the published mineralogical, bulk and clay-fraction geochemical, and clay-fraction O-isotopic compositions of 2 shales. One shale is from the Western Canada Sedimentary Basin (WCSB), and its composition mainly reflects primary (depositional) chemical and mineralogical variations (smectitic to illitic illite/smectite) within this unit. The other shale is from the United States Gulf Coast (USGC), and its composition mainly reflects mixed-layer illite/smectite (I/S) diagenesis of deposited smectitic clay material. The chemical and mineralogical trends of WCSB and USGC shales, including one of increasing illite content in I/S with depth or maturity, are essentially indistinguishable, in both bulk shale and clay fraction, despite the contrasting genetic interpretations for the origin of the contained I/S. Thus, similar mineralogical and chemical trends with depth or temperature can result either from inherited depositional compositional heterogeneity of the sediment, from burial metamorphism of shale or a combination of both. Interestingly, the O-isotopic compositions of the clay fractions from the WCSB and USGC are significantly different, a fact that reflects original clay formation from source material and water of quite different isotopic compositions. The discrimination between depositional and diagenetic contributions to shale composition continues to pose challenges, but a combination of bentonite, illite polytype, clay isotopic and trace and rare earth elemental analyses together with illite age analysis holds promise for future work.

Mineralogy and geochemistry of Mesozoic black shales and interbedded carbonates, southeastern Sicily: evaluation of diagenetic processes

AbstractUpper Triassic/Lower Jurassic organic-rich shales and interbedded carbonates (Rhaetian → Sinemurian) are widespread in the subsurface of southeastern Sicily where important oil fields have been found hosted in Triassic reservoirs. Core samples from wells drilled offshore and onshore were studied from petrographie and geochemical viewpoints.In the Hettangian/Sinemurian shale-carbonate sequences, which accumulated in a rapidly subsiding basin, the micritic aragonitic mud is still largely preserved. Mixed-layer I/S has remained randomly interstratified to a depth > 4000 m. Diagenetic carbonates are non-stoichiometric finely crystalline, pore-filling dolomite and/or calcite. The carbonate component exhibits a high Sr content and fair amounts of Fe and Mn. Carbon and oxygen isotopic values suggest a subsurface interstitial formation for the digenetic carbonates in an essentially closed system. Based on all accumulated data it is suggested that anoxic marine waters were retained in the sediment pores for a long time after deposition, thus enhancing the preservation of significant amounts of the original organic matter.In contrast, Rhaetian tidal-flat deposits hosting black shales display a clay component characterized by ordered illite-rich I/S and a carbonate mineralogy dominated by low-Mg calcite in the uppermost beds and by near-stoichiometric dolomite in the lowermost ones. Petrographie, chemical and isotopic data indicate early cementation in an oxidizing phreatic environment and lower down in the sequence pervasive dolomitization in a sabkha-type environment.

Relationship between clay mineralogy and thermal maturity of Neogene-Quaternary shales in Ras El-Barr well, offshore Nile Delta, Egypt

The basin of the Nile Delta contains a thick section of Neogene-Quaternary strata that have different values of thermal maturity as determined by vitrinite reflectance. The study area in the eastern part of the offshore Nile Delta basin is represented by the Ras El-Barr well No.1. Clay mineralogy, the half-width of the 10Å illite and 7Å chlorite peaks, and the A H values (area under peak/peak height) are systematically related to thermal maturity. The most important changes in clay minerals with increasing depth of burial are the regular reduction of expandable layers and the gradual increase in the crystallinity of illite and chlorite (decrease of the half-width value) with depth. The results of this study suggest that, in the absence of vitrinite, the values of the half-width of the 10Å peak and the A H value of illite (especially glycolated) may be used to quantitatively estimate the levels of thermal maturity and consequently as indicators to differentiate source rocks above and below the oil generation threshold and to approximate the hydrocarbon generation and preservation stages of potential source rocks.

Inorganic geochemistry and mineralogy of unit B, Duaringa oil shale deposit

Chemical and mineralogical analyses are presented for a continuous sequence of samples over the full stratigraphic section of Unit B, Duaringa oil shale deposit. Correlation techniques and electron microprobe analysis have been used to determine element and mineral associations and the composition of manganoan siderites. The work presented provides a detailed chemical and mineralogical description of the unit. The geochemistry and mineralogy of Duaringa oil shales is similar to that of other Tertiary oil shales excepting that the composition of manganoan siderite crystals is unusually variable. A number of minerals show systematic trends with stratigraphie depth and oil shale grade in Unit B. In particular, pyrite correlates positively and manganoan siderite correlates negatively with oil shale grade. Manganoan siderites were inversely variable in manganese and iron content within individual grains. Manganese contents increased progressively from 1 wt% MnO at the extremities to as much as 15 wt% MnO in the central regions of some grains. This may reflect decreasing availability of manganese in the pore liquors as crystallization proceeded during early diagenesis.

The oxidation of pyrite in cement stabilized colliery shale

Abstract This paper reports a study into the long-term performance of cement stabilized colliery shale. A total of 16 samples were obtained from various UK collieries chosen to provide shales with a representative range of physical and chemical properties. Cement stabilized specimens produced from these shales were exposed to three different environments. The engineering performance of the stabilized specimens was established through the monitoring of changes in linear dimensions and strength. The sulphur-bearing mineralogy was examined at regular intervals, and the samples were analysed by X-ray diffraction and scanning electron microscopy throughout the study. It is concluded that pyrite, a component of colliery shale, oxidizes in cement stabilized shale. The products of pyrite oxidation may cause distress in the stabilized material through the generation of crystallization pressures or, alternatively, may attack cement hydration minerals. The long-term performance of the stabilized shale is reliably correlated with the original sulphur-bearing mineralogy of the raw shale. Establishment of the limits of total, pyritic and sulphate sulphur are suggested to preclude the use of shales which may cause problems to the long-term durability of cement stabilized colliery shale.

Sedimentology, Petrology and X-ray Mineralogy of Coniacian-Santonian Niobrara Shale, Northeastern San Juan Basin, New Mexico: ABSTRACT

Sedimentology, Petrology and X-ray Mineralogy of Coniacian-Santonian Niobrara Shale, Northeastern San Juan Basin, New Mexico: ABSTRACT

Metamorphic control of the magnetic mineralogy of black shales in the Swiss Alps: toward the use of “magnetic isogrades”

The magnetic susceptibility of the Helvetic Jurassic black shales, sampled around the Aar and Gothard massifs in the Swiss Alps, is due to iron-bearing silicates, magnetite or pyrrhotite. It exhibits a clear correlation with the Alpine metamorphism, from zeolite to amphibolite facies: it firstly decreases due to the breakdown of original magnetite, then sharply increases when pyrite is transformed into magnetic pyrrhotite. Using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite-in isograde, which appears to correspond closely to the stilpnomelane-out isograde. The matrix susceptibility, obtained by means of high-field measurements with a cryogenic magnetometer, is due to iron-bearing silicates and shows only smooth variations with metamorphism. Both monoclinic and hexagonal pyrrhotites are observed in the high-grade area.

Mineralogy and Lithology of Utah Oil Shale and Their Influence on Logging Response: ABSTRACT

Detailed mineralogic and lithologic investigations of the Green River Formation oil shale in Uintah County, Utah, indicate unusual properties which strongly influence certain wireline logging responses. Those logging parameters considered include density, gamma, relative dielectric constant, resistivity, and magnetic susceptibility. Two 160-ft cores, comprising the Mahogany Zone and an adjacent section approximately 40 ft above and below this unit, were cut, slabbed, and analyzed. Lithologically, the cores consist predominantly of laminated oil shale and marlstone with minor sandstone and altered tuff. Mineralogically, the oil shale contains dolomite, calcite, quartz, Na-feldspar, K-feldspar, smectite, illite, iron sulfides, and scattered siderite, aragonite, and analcime. Petrographic studies (thin section, SEM/EDS and XRD) indicate that iron sulfides occur both dispersed in the oil shale and concentrated along certain laminae. These iron sulfides, identified as pyrrhotite, pyrite, and marcasite, form blades, pods, cubes, and aggregates. In particular, pyrrhotite is highly conductive and magnetic and, when concentrated along thin, continuous laminae, markedly affects the electrical properties of the oil shale. Results of the study determined that the logging response reflects the bulk composition of the rock and is strongly influenced by the pyrrhotite-rich laminae and the amount of moisture in the shale.

Relationships Among Vitrinite Reflectance, Illite Crystallinity, and Organic Geochemistry in Carboniferous Strata, Ouachita Mountains, Oklahoma and Arkansas: REPLY

The Ouachita Mountains contain a thick section of Carboniferous strata that display an extreme range in thermal maturity as determined by vitrinite reflectance. Clay mineralogy, illite crystallinity, and organic geochemistry of shales from those strata are systematically related to thermal maturity. Shales of the Stanley, Jackfork, and Atoka formations are predominantly composed of illite and chlorite with minor occurrences of mixed-layer clays (restricted to samples characterized by mean vitrinite reflectance less than 1.5%) and pyrophyllite (restricted to samples characterized by mean vitrinite reflectance greater than 2.7%). Illite crystallinity is significantly related to vitrinite reflectance (Ro). Weaver's illite sharpness ratio (SR) increases with increasing Ro: log (SR) = 0.28 + 0.08 (Ro); whereas Kubler's illite crystallinity index (CI) decreases with increasing Ro: log (CI) = 1.01 - 0.07 (Ro). Plots of bitumen ratio (bitumen/total organic carbon) vs. vitrinite reflectance, Weaver's illite sharpness ratio, and Kubler's crystallinity index all reveal hydrocarbon generation-preservation curves that define submature, mature, and supermature zones with regard to a liquid hydrocarbon window. These results suggest that, in the absence of vitrinite, illite crystallinity can be used quantitatively to estimate levels of thermal maturity and cautiously to approximate hydrocarbon generation-preservation stages of potential source rocks.

Organic geochemistry of the British Kimmeridge clay: 2. Acyclic isoprenoid alkanes in Kimmeridge shale oils

The C15C20 isoprenoid alkane composition of Kimmeridge Clay shale oils produced by Fischer assay has been examined, and compared with the isoprenoid composition of corresponding bitumens. C16 and C18 isoprenoid alkanes are generally dominant in shale oils, while pristane (C19) and phytane (C20) dominate in bitumens. A significant proportion of the phytane in many shale oils is derived from simple evaporation of free (bitumen) phytane, while free pristane contributes less to shale oil composition. Some shale oil phytane and a large proportion of pristane is kerogen-derived. Certain shale oils contain lower concentrations of isoprenoid alkanes than corresponding bitumens, suggesting that some free alkane is thermally degraded during pyrolysis. Results thus indicate three sources for shale oil isoprenoid alkanes: thermal evaporation of free alkanes (particularly for phytane), kerogen decomposition, and possibly the cracking of higher homologues for C15C19 alkanes. Kerogen-derived isoprenoids are suggested to arise by thermal desorption of adsorbed free alkane (particularly for phytane) and from CO and CC bonded species (excluding phytane) via postulated clay catalysed hydrogenation of initially formed alkenes. Comparison of shale oil and bitumen pristane/phytane ratios allows groups of oil shales to be defined, dependent on source composition, organic carbon content and maturity. Shale oil pristane/phytane ratios can also help to determine depositional environments and source composition, although maturity, shale mineralogy and competing alkene-forming pyrolytic reactions may also affect the ratios.

Relationships Among Vitrinite Reflectance, Illite Crystallinity, and Organic Geochemistry in Carboniferous Strata, Ouachita Mountains, Oklahoma and Arkansas

The Ouachita Mountains contain a thick section of Carboniferous strata that display an extreme range in thermal maturity as determined by vitrinite reflectance. Clay mineralogy, illite crystallinity, and organic geochemistry of shales from those strata are systematically related to thermal maturity. Shales of the Stanley, Jackfork, and Atoka formations are predominantly composed of illite and chlorite with minor occurrences of mixed-layer clays (restricted to samples characterized by mean vitrinite reflectance less than 1.5%) and pyrophyllite (restricted to samples characterized by mean vitrinite reflectance greater than 2.7%). Illite crystallinity is significantly related to vitrinite reflectance (Ro). Weaver's illite sharpness ratio (SR) increases with increasing Ro: log (SR) = 0.28 + 0.08 (Ro); whereas Kubler's illite crystallinity index (CI) decreases with increasing Ro: log (CI) = 1.01 - 0.07 (Ro). Plots of bitumen ratio (bitumen/total organic carbon) vs. vitrinite reflectance, Weaver's illite sharpness ratio, and Kubler's crystallinity index all reveal hydrocarbon generation-preservation curves that define submature, mature, and supermature zones with regard to a liquid hydrocarbon window. These results suggest that, in the absence of vitrinite, illite crystallinity can be used quantitatively to estimate levels of thermal maturity and cautiously to approximate hydrocarbon generation-preservation stages of potential source rocks.

The influence of clay mineralogy and diagenesis of Upper Carboniferous shales on soil formation in parts of Devon

SUMMARYThere is a correlation between variations in the clay mineral assemblages of the Crackington Formation (Upper Carboniferous) shales in parts of Devon, and the soil series mapped in the same areas. The differences in soil‐forming characteristics of the shales are not due to mineralogy alone, but to various states of diagenetic induration which they have achieved. Brown earths (Dunsford series) are formed on steeper slopes of more durable, illite‐chlorite dominated shales, whereas clayey soils (Tedburn and Halstow series) are typical of flatter, more poorly drained slopes of weaker illite and illite‐kaolinite clay mineral assemblages. This result adds the geological component to earlier views that the different soil series are simply a consequence of physiographic and hydrologic position.

The application of simultaneous DTA and TG to some aspects of oil shale mineralogy

The mineralogy of most Australian oil shales is relatively simple and belongs to the carbonate, clay, sulphide, sulphate, silica, phosphate, zeolite and evaporite/saline mineral groups. Retorting involves heating during which virtually all oil shale minerals react. Such reactions, endothermic or exothermic may be characterised and measured by DTA, whilst associated weight variations may be continuously quantified by TG. These methods provide mineralogical identification and evaluation data, together with reaction type, magnitude and heat balance information, obtained under heating rate and gas atmosphere conditions preselectable to simulate various retorting conditions. Endothermic and exothermic mineral reactions taking place within the retort may strongly influence the required retort heat balance regime. Detailed knowledge of the actual minerals present, their quantities, reaction temperatures and types, together with heat balance effects are of marked technological importance to the design and operation of oil shale retorts and the assessment of spent shale characteristics and potential utilisation.

Geochemical Study of Depletion of Elements During Retorting of Oil Shales from Lewis County, Kentucky: ABSTRACT

The prospect of oil shales as an alternative means of hydrocarbon production has sparked concerns as to the chemical composition of the original shale as well as that of the spent shale, oil, water, and gas fractions produced due to retorting. This study is concerned with a chemical concentration comparison between raw and spent shales from Lewis County, Kentucky. Eighteen elements (Si, Ti, Al, Fe, Mg, Ca, Na, K, P, Ba, Co, Cr, Cu, Mo, Ni, Pb, V, and Zn) were investigated in two shale lithologies: the Sunbury and Cleveland Shales. Three slightly different modified Fischer Assay procedures were compared for their effects on the resulting spent shale chemistry. Two procedures employed sweep gases (nitrogen and steam), while the third used no gas sweep. The heating rates dur ng the procedure were also varied. It was found that the employment of a sweep gas throughout the retorting procedure induces a measurable degree of depletion over a no gas sweep procedure. The gas flow enhances the effectiveness of pyrolysis, and aids in the formation of aerosols in which elements are carried out of the retort to be condensed in the oil and water fractions. It was also found that differences in original shale mineralogy (e.g., elemental substitutions in major minerals and trace mineral compositions) was responsible for differential elemental depletions seen in the two lithologies. End_of_Article - Last_Page 527------------