Conversion Of Kerogen Research Articles

Numerical models of petroleum migration via buoyancy‐driven porosity waves in viscously deformable sediments

AbstractThe apparent ability of petroleum to migrate rapidly through low permeability sediments in sedimentary basins has led to many questions about the manner of its transport. One possible explanation is suggested from observations of the compaction of viscously deformable porous media. These systems have been found in some cases to give rise to regions of locally elevated liquid fraction, in the form of fluid‐filled porosity waves that can ascend at rates much greater than that of the background flow. Previous research on the phenomenon has focused on its implications for magma transport, but recognition of the fact that the compaction of viscous porous media can take place in sedimentary basins has suggested the possibility that porosity waves could similarly be important for hydrocarbon transport. The purpose of the present study was to test this hypothesis by quantifying the transport that would occur as the result of porosity waves initiated during the conversion of kerogen to petroleum.A one‐dimensional numerical model was constructed solving equations for the mechanics of viscous compaction and for the kinetics of reactions describing the formation of petroleum from kerogen. The results showed that porosity waves would develop readily in viscously deformable regions of sedimentary basins, but would not necessarily provide enhanced transport over that of the background flow regime. In order for the waves to achieve this enhanced transport, they must develop high amplitudes, i.e. high porosities relative to the background porous medium. To achieve the high wave amplitudes, the background porosity must be very low in absolute terms. In addition, high kerogen contents are needed in the source layer, and the source layer needs to be buried rapidly to a high temperature region of the oil window. Considerable uncertainty exists as to the value of the matrix shear viscosity of sediments in basins. However, the wave volumetric transport capacity was not found to be significantly altered as a result of variations in the value of this parameter. The physical form of the waves was strongly altered by the matrix shear viscosity, with higher values leading to lower amplitudes and generation frequency, but higher wavelengths. Thus the waves become less recognizable physically at higher values of the matrix shear viscosity. As the waves ascend to higher stratigraphic levels, where the porosity is higher, they gradually lose their physical definition and become absorbed into the background.

A model for seismic velocity and attenuation in petroleum source rocks

Petroleum source rock is modeled as a viscoelastic transversely isotropic medium composed of illite/smectite and organic matter. The wave velocities and attenuation of petroleum source rocks are obtained as a function of excess pore pressure, initial kerogen content, and water saturation. The model generalizes a previous approach based on a pure elastic formulation of Backus averaging and introduces the pressure effect and the presence of fluids (oil and water). The model allows the simulation of different maturation levels induced by pore‐pressure changes caused by the conversion of kerogen to oil. The higher the oil saturation, the higher the maturation level. Assuming that the source rock has a very low permeability, the excess pore pressure can be calculated as a function of the conversion factor. Then the bulk modulus and density of the kerogen/oil mixture are obtained with the Kuster and Toksöz model, assuming that oil is the inclusion in a kerogen matrix. Finally, Backus averaging of this mixture with the illite/smectite layers gives the complex stiffnesses of the transversely isotropic and anelastic medium. Computed P- and S-velocities and quality factors parallel to bedding are higher than those normal to bedding, with attenuation anisotropy higher than stiffness anisotropy. In particular, for the North Sea Kimmeridge Shale and at maximum anisotropy, P and S parallel velocities are approximately 0.7 km/s higher than the corresponding P and S normal velocities. The maximum attenuation and stiffness anisotropies are obtained for 18% and 30% volumetric kerogen content, respectively. Both velocities and quality factors decrease with increasing kerogen content at a given pore pressure. The decrease in wave velocity is 2 km/s for P-waves and 1 km/s for S-waves when kerogen increases from zero to 100%. Moreover, anisotropy increases and velocities decrease with increasing pore pressure, i.e., with higher kerogen‐to‐oil conversion. Finally, the presence of water affects the normal‐bedding velocity, i.e., higher water saturation implies lower velocities.

Effect of the mineral matrix in the reactions of oil shales: 1. Pyrolysis reactions of Turkish Göynük and US Green River oil shales

The effect of the mineral matrix of Turkish Göynük and Green River oil shales on the conversion of kerogen into organic material in pyrolysis reactions was investigated in this study. The conversion of kerogen to volatile organic material in pyrolysis reactions increased with increased reaction temperatures for the original and demineralized products of oil shales. Increasing the heating rate also caused greater kerogen conversion. It was found that pyrolysis reactions were catalyzed by alkaline earth metal cations in carbonates and inhibited by silicates. The inhibition effect of the silicates seemed to be greater than the catalytic effect of the carbonates in the pyrolysis reactions of the original Göynük and Green River oil shales.

Abstract: Kerogen Conversion in Fractured Shale Petroleum Systems

Abstract: Kerogen Conversion in Fractured Shale Petroleum Systems

Geopressuring Mechanism of Organic Matter Cracking: Numerical Modeling

Since the 1950s, hydrocarbon generation has been considered as one of the most important abnormal pressuring mechanisms. Hydrocarbon generation effects on pore-pressure evolution: (1) it increases the pore fluid volume through the conversion of solid kerogen into liquid or gaseous hydrocarbon, and (2) it decreases the sediment permeability because hydrocarbons remain an immiscible phase in pore water. In this paper, the two products of organic matter decomposition, liquid hydrocarbon (oil) and gaseous hydrocarbon (methane), are assumed to occur in sequence as a supplementary phase in pores as a basis for evaluating the effect of this pressuring mechanism. A simplified three-stage first-order kinetic reaction model is applied to simulate the generation of oil and gas. We u e a numerical basin model with a two-phase hydrodynamic formulation to calculate the effect of organic maturation on geopressure evolution. Oil generation does not play an important role except when the organic matter content of rocks is relatively large (>5%); however, the generation of gas has a large influence. The results show that beneath a certain depth, oil-to-gas cracking strongly influences overpressuring. The effect of this mechanism becomes more important with increasing organic matter content of rocks. Several environmental conditions, such as kerogen type, temperature gradient, and lithological characteristics, influence to various degrees the effect of organic matter maturation on overpressure development.

Modeling thermogenic gas generation using carbon isotope ratios of natural gas hydrocarbons

An isotopic model to predict δ 13C values for methane (C 1), ethane (C 2), and propane (C 3) as a function of fractional conversion of kerogen and/or oil to gas is proposed for gas generation from Type II kerogen. Fractional conversion is then correlated to gas generation temperature by coupling the isotopic model to a multicomponent compositional kinetic model for gas generation. The relationships between δ 13C 1, δ 13C 2 and δ 13C 3 are constrained by the natural gas plot model of thermal cracking. The isotopic model has been tested and calibrated using a data set of gas samples derived from sapropelic marine shales (Type II kerogen) in the Delaware and Val Verde basins, West Texas. These gases are relatively unaffected by migration or mixing of biogenic gas, so that changes in carbon isotope ratios of the gas components primarily reflect the effect of maturation. This data set is therefore useful for illustrating the relationship between gas generation temperature and δ 13C values for gases derived from Type II kerogen. Several applications of the isotopic /compositional kinetic model in petroleum system evaluation are discussed. The effect of burial history on the relationship between δ 13C 1δ 13C 3 and gas generation temperature can be determined from the coupled models. Also, δ 13C values of C 1C 3 observed in the reservoir will depend on whether gas accumulates from source to trap, or whether it is expelled at various stages into several traps. Both trapping scenarios can be examined using the isotopic/compositional kinetic model. Separate isotopic models are needed for gases derived from Type II versus Type III kerogens because of the larger difference between δ 13C 1 and δ 13C 2 observed for gases generated from terrestrial organic matter. This larger difference may result from greater molecular or isotopic heterogeneity in Type III kerogens, or may reflect differences in generation and/or accumulation of gases from the differing kerogen types.

Multiple Cold Trap Pyrolysis Gas Chromatography: a new technique for modeling hydrocarbon generation

The newly developed Multiple Cold Trap Pyrolysis Gas Chromatography (MCTP-GC) technique allows us to calculate activation energies for the generation of individual hydrocarbons from source rocks. This improves our ability to predict the timing of oil generation and the compositional changes of oil at the different stages of kerogen conversion. The activation energies for n-C 12 and n-C 24 for a Type II kerogen (Toarcian Shale) are 57.5 ± 0.8 kcal/mol and 51.2 ± 2.2 kcal/mol with frequency factors of 8.71 × 10 16/min and 1.15 × 10 15/min, respectively. The relative rates of alkane generation are n-C 24 > n-C 18 > n-C 12 > n-C 2−C 5. By comparing the rates of generation from kerogen and asphaltenes for Monterey source rocks, we conclude that normal alkanes can be generated directly without going through an asphaltene intermediate.

Are time and temperature the only constraints to the simulation of organic matter maturation?

Confined pyrolysis, hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples (Toarcian shale and kerogen, Woodford shale and kerogen, Manakam coal) and under different experimental conditions, in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter. Results show that: (i) experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models; (ii) increasing confining pressure (300–1300 bars) in gold cell experiments performed on Woodford samples has a limited influence on the reduction rate of the oil potential, the TSOM (Total Soluble Organic Matter) yield and the structure of the polars; (iii) the presence of excess liquid water (0–100 weight %) in confined pyrolysis experiments does not significantly influence organic matter maturation. However, comparisons with classic hydrous pyrolysis (200 weight % water) could indicate major differences in timing and composition of the TSOM (bitumen + expelled fraction) as well as of the solid residue. It appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined. Hydrous pyrolysis conditions (low partial pressure of products) delay Woodford kerogen conversion. In addition, results concerning the Mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect; (iv) increasing water pressure in hydrous conditions (220–1300 bars) drastically lowers and delays Woodford kerogen maturation. Quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis. This study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation.

Characterization of shale oils. 2. Analysis of the flash pyrolysis products of oil shale in the Green River Formation

The results of experiments to rapidly pyrolyze oil shale from the Green River Formation using a xenon flash lamp reactor are presented. A variety of analytical tools were used to determine the composition of the liquid products and to compare the rapid pyrolysis products with those from conventional retorting processes. The tools included infrared, proton nuclear magnetic resonance, high performance liquid chromatography and field ionization mass spectroscopy. The reaction mechanisms of rapid pyrolysis were found to be different from those of slow-heating rate processes. Thermal fragmentations were non-selective, resulting in a broad range of high molecular weight components that contained more heteroaromatic functionality than in the products of conventional retorting. Other reactions that were found to differ in slow versus rapid pyrolysis were dehydrogenation of hydroaromatic compounds and formation of condensed and noncondensed aromatic compounds. As the input energy to oil shale is increased, even though the oil shale was heated to high temperatures, the liquid products still contained significant amounts of alkanes and olefins. Based on these results, the high conversion of kerogen by rapid pyrolysis produces a low quality fuel which would require upgrading before utilization.

Vanadyl porphyrins in exploration: maturity indicators for source rocks and oils

The Porphyrin Maturity Parameter ( PMP), which is derived from the vanadyl porphyrin distribution, is an excellent parameter for: (1) identifying the zone of hydrocarbon generation from marine source rock extracts; and (2) determining from oils the thermal maturity of their source rocks at expulsion. The PMP is measured using a methodology which is inexpensive, reliable and faster than earlier methods, allowing it to be used as a routine exploration tool. The PMP may be a more reliable maturity indicator for marine organic matter than some conventional methods such as vitrinite reflectance. Unlike most conventional maturity parameters guided by processes other than kerogen conversion, the reactions causing PMP evolution directly monitor the generation of bitumen and the concurrent thermal degradation of kerogen. Measurements on hydrous pyrolyzates from the Monterey Formation (offshore California), source rock bitumens from the Devonian-Mississippian Bakken Shale (Williston Basin), and Miocene Monterey equivalent source strata (San Joaquin Basin, California) illustrate the method. In all cases reviewed so far, PMP begins increasing at the onset of hydrocarbon generation and increases systematically and predictably as kerogen decomposition proceeds. In oils generated from high-S marine kerogens, PMP reflects the maturity of the source rock at the time of oil expulsion, provided that the oil does not undergo subsequent reservoior maturation or mixing with in-situ bitumen.

The determination of a complex kinetic expression of oil shale pyrolysis using combined non-isothermal and isothermal TG

The kinetic expression commonly used in the thermal analysis of oil shale pyrolysis was derived on the basis of a simple first order kinetic equation of kerogen decomposition. The activation energy, as well as the reaction rate constant of oil shale pyrolysis could be determined by using non-isothermal (NI) or isothermal (I) TG. However, the kinetic parameters determined by using either NI or I did not enable the good prediction of the kerogen conversion at other conditions. The comparative results of the NI and I-TG of different oil shales are discussed in the study, as well as the effects of the so-called combined non-isothermal and isothermal TG (NI/I). The obtained results indicate that a mechanism must be postulated based on a complex reaction scheme which involves more than one simple reaction.

The Art of Maturity Modeling, Part 1: Finding a Satisfactory Geologic Model (1)

An example of one-dimensional maturity modeling of the MITI Rumoi well, a stratigraphic test drilled in a frontier area of Japan, is worked out in detail to illustrate how maturity modeling should be carried out. Prior to and during modeling, an effort was made to integrate all available geological, geochemical, and geophysical concepts and data to create a single geologic model (called here the good model) that was as plausible and internally consistent as possible. Where data sets were internally inconsistent or in conflict with other data, decisions had to be made about data reliability. Some vitrinite-reflectance data, subsurface temperatures, and thermal conductivity measurements were rejected for a variety of reasons. The justifications for these decisions, which influenced the results of the modeling, are discussed in detail. Using the good model, we evaluated the timing and amount of oil and gas generation from coals in the Haboro Formation, the only proposed source rocks in northwest Hokkaido, Japan. Generation has occurred continually since the middle Miocene, but the fractional conversion of kerogen to hydrocarbons to date has been small. As a result, the total volume of hydrocarbons available for expulsion and migration from the Haboro source rock probably is small unless very large volumes of coal are present. The good model does not represent a unique solution, however. It thus should be regarded as one of a number of viable models rather than as the only correct one. Alternative models are considered in a companion paper. The modeling process itself, by which and during which we learn much about the geologic system, is at least as important as the final numerical answer. Highly interactive modeling programs greatly aid in proper modeling.

A new method for the measurement of kinetic parameters of hydrocarbon generation from source rocks

A new laboratory technique for the determination of the kinetic parameters of hydrocarbon generation has been developed. It measures separately the reaction rate's dependence on the temperature and on the degree of kerogen conversion. The method allows the direct determination of the activation energy of generation and makes no assumptions about the pre-exponential factor or the reaction order. The kinetic parameters of hydrocarbon generation from source rocks of the major kerogen types have been examined. There are wide variations in the isothermal reaction rates; measured activation energies lie mainly in the range from 46 to 56 kcal/mol (190–235 kJ/mol). The differing kinetic behaviour is compared with the elemental compositions of the kerogens. Using a numerical integration method, the kinetic data can be extrapolated to geological heating rates and compared with estimates of conversion for naturally mature source rock samples.

Dynamic behavior of supercritical extraction of kerogen from shale

AbstractA model is presented for the supercritical reaction‐extraction of a solid component from a bed of porous particles through which the solvent flows. Accounted for are reaction at an intraparticle position, pore diffusion, interphase mass and heat transfer, and flow in a differential reactor. The behavior of the bed is dynamic since both temperature and concentration of extractable solid vary with time.The model is compared with experimental data for the extraction with toluene of kerogen from a bed of Colorado shale particles. Curves of effluent bitumen concentration vs. time were measured and fitted with predicted curves to evaluate three parameters: preexponential factor and activation energy for the conversion of insoluble kerogen to soluble bitumen, and the diffusivity of toluene at the critical point. The predicted curves agreed well with the experimental results and gave reasonable values for the parameters. Rates of reaction‐extraction as well as extraction curves exhibited a sharp dip as the reactor was heated through the critical temperature.

ESR studies of kerogen conversion in shale pyrolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTESR studies of kerogen conversion in shale pyrolysisB. G. Silbernagel, L. A. Gebhard, M. Siskin, and G. BronsCite this: Energy Fuels 1987, 1, 6, 501–506Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://doi.org/10.1021/ef00006a008RIGHTS & PERMISSIONSArticle Views104Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (767 KB) Get e-Alerts Get e-Alerts

Kinetic and reaction engineering model for thermal solution of oil shale in FCC decant oil

Fundamental reaction kinetics and reaction stoichiometry are developed for thermal solution of oil shale based upon analysis of data from 67 runs on a once-through, continuous stirred-tank reactor (CSTR) bench-scale unit using FCC decant oil as the solution medium. A material-balanced model of the CSTR is used in conjunction with nonlinear optimization theory to derive estimates of the kinetics parameters and stoichiometric coefficients. Reactions occur in the liquid phase and are of two basic types: thermal conversion of kerogen to form heavy oil and cracking of the liquid oils to form lower boiling oils, gases, and residue, i.e., coke. The reaction paths, described in terms of pseudocomponents which lump narrow boiling range cuts of oil, involve a cascading series of reactions in which components in each boiling range cut undergo first-order cracking to form components in lower boiling ranges. Each reaction rate is expressed in terms of the classical Arrhenius temperature dependence multiplied by the concentration of the pseudocomponent boiling cut. Concentration dependence is first-order for all psuedocomponents. The kerogen decomposition rate parameters are comparable to literature values for conventional pyrolysis approaches. Model predictions for kerogen conversion and product yield structure agree well with the experimental data.

Identification by 13C n.m.r. of carbon types in shale oil and their relation to pyrolysis conditions

A number of samples of shale oil prepared under various conditions have been examined by 13C n.m.r. using multiple-pulse techniques that allow carbon-type assignments. Previous assignments by Netzel et al. ( Fuel 1981, 60, 307) are confirmed and several new ones made. Product chemistry is then examined as a function of heating conditions. New or verified observations are: 1. (1) isoprenoids are evolved in the early stages of oil generation, and the average length of normal hydrocarbons in the evolved oil is approximately independent of the extent of kerogen conversion; 2. (2) alkene content depends strongly on the heating rate during pyrolysis but average normal chain length does not; and 3. (3) the ratio of isoprenoid to normal carbons and the average normal chain length in bitumen are greater than in shale oil, but there are greater questions about the correct equation for calculating the average normal chain length of bitumen.

Low-temperature oil shale conversion

The process approach of low-temperature oil shale conversion is focused on heating the shale at a relatively low temperature, in the presence of hydrogen such that kerogen is converted to products that are toluene-extractable. The conversion of kerogen to gas and residue coke is minimized under low-temperature conditions.

Thermal mechanisms of basin formation

Thermal subsidence of the sea floor explains the observed bathymetry of ocean ridges. A similarity solution for a one-dimensional cooling model successfully predicts bathymetry, heat flow and geoid anomalies under a wide range of conditions. This similarity solution can be modified to predict the thermal subsidence of sedimentary basins. For older sedimentary basins it is necessary to consider an input of heat to the base of the lithosphere that places a limit on subsidence. The similarity solution for thermal subsidence is in quite good agreement with the observed subsidence history of a variety of sedimentary basins. Some basins subside freely and in others the flexural rigidity of the elastic lithosphere inhibits subsidence. An empirical model is proposed for the conversion of kerogen to oil and the subsequent conversion of oil to gas. This model is then used in conjunction with the thermal evolution predicted by the similarity solution in order to determine the oil window and relative volume of oil as a function of the age of the basin.

Abnormal Pressures Produced by Hydrocarbon Generation and Maturation and Their Relation to Processes of Migration and Accumulation: ABSTRACT

Abnormally high pore-fluid pressures may be produced as a result of hydrocarbon generation from organic matter (kerogen) contained in Contributing processes include: (1) collapse of rock matrix as overburden-supporting solid kerogen is converted to non-expelled fluid hydrocarbons and (2) volume increases produced by the conversion of kerogen to hydrocarbons. Overpressures may also be created by volume increases associated with the thermally progressive conversion of oil to wet gas/condensate and to dry gas within the pores of either the source rock or associated isolated hydrocarbon-saturated nonsource rocks. Generation-type overpressures may be reinforced or maintained by (1) fluid-volume expansions caused by higher temperatures associated with further bu ial and by (2) capillary entry pressure phenomena associated with expulsion/migration. The occurrence, maintenance, and degree of fluid overpressuring appear to be dependent on time, temperature, volume of kerogen/hydrocarbons undergoing transformation, and the relative isolation of the rocks with respect to regionally extensive high-permeability rocks. Regions of hydrocarbon-generation overpressure have been documented in several basins. They are present as vertically and laterally restricted or pods centering around actively generating source-rock units in basin-bottom positions. Hydrocarbons in most places appear to be the overpressuring fluid and the only initially producible fluid species present. Actively generating source rocks within the pressure cells may be characterized by (1) abnormally high electrical resistivities and abnormally low sound velocities. Resistivity increases may be caused by the replacement of conductive pore water with nonconductive hydrocarbons. Low sound velocities may be caused by (1) the replacement of higher velocity pore water with lower velocity hydrocarbons and (2) the effects of abnormal pressure on porosity enhancement or preservation through dilation or undercompaction. Overpressures produced by hydrocarbon generation are the primary motivating forces causing primary expulsion from source rocks to conventional reservoir rocks. These overpressures may cause the spontaneous hydraulic fracturing of a source rock. The process facilitates fluid expulsion and may also create an associated in-situ fracture-type reservoir. The process may also create far-reaching fractures which propagate upward or downward from the source rocks and control vertical migration through great thicknesses of seemingly impermeable confining strata. After active high-rate hydrocarbon generation has ceased in a basin, owing either to (1) decreases in temperature produced by uplift or lower heat flow or to (2) loss of generation capacity due to over-maturity, the associated pod of abnormally high pressures may be replaced by a pod of abnormally low pressures associated with closed apparent minimum potential energy (potentiometric) sinks. This stage of pressure evolution is controlled by the imbibition of water into the initially overpressured area of high hydrocarbon saturation. Contributing processes may include (1) the volume contraction of pore-fluid hydrocarbons caused by decreases in temperature, (2) the establishment of topographically introduced hydrodynamic conditions, (3) the solution-diffusion of hydrocarbons (prima ily methane) outward from the system, and (4) the capillary imbibition of water. Significant accumulation of hydrocarbons in highly unconventional basin-bottom positions may occur in either the overpressured or underpressured stages of basin hydrocarbon generation-migration evolution. When water is imbibed into the original site of hydrocarbon generation and overpressure, and the associated unstable localization of hydrocarbon saturation has been dissipated and destroyed during an associated stage of underpressure, pore pressure conditions will eventually return to near normal states. End_of_Article - Last_Page 2467------------