Single Frequency Factor Research Articles

Quantitative analysis of thermoluminescence signals of glass displays from mobile phones

Glass displays from mobile phones show a characteristic thermoluminescence (TL) signal after the exposure to ionizing radiation. Therefore they can be used as accident and emergency dosimeters. This paper carries out quantitative analysis of such TL signals by using several standard methods of analyzing luminescence signals. Application of the initial rise method to 120 TL glow curves obtained by the Tmax-Tstop method, shows that the TL signals can be described by a quasi-continuous distribution of energies in the range of E=0.8-1.5 eV. The shape of the TL signals was simulated by using five Gaussian trap energy distributions centered at five discrete activation energy values and a single frequency factor s. The result of the simulations were in a good quantitative agreement with all the experimental TL glow curves. Two additional experiments investigating the variation of the TL signal with the heating rate, and studying the fading of the TL signal at room temperature over long periods of time, showed that this material exhibits the well known anomalous heating rate effect, and anomalous fading of the TL signal. The results of these two experiments demonstrate that the luminescence mechanism in this dosimetric material is rather complex, and that additional recombination pathways affect the luminescence process during a TL measurement.

Passive temperature sensing using thermoluminescence: Laboratory tests using Li2B4O7:Cu,Ag, MgB4O7:Dy,Li and CaSO4:Ce,Tb

The objective of this work is to test three thermoluminescent (TL) materials, Li2B4O7:Cu,Ag (LBO), MgB4O7:Dy,Li (MBO) and CaSO4:Ce,Tb (CSO), as passive temperature sensors. Particles of these materials were subjected to two heating profiles: (a) a slow heating profile (2h inside a muffle furnace) or (b) a fast heating profile (dropping them through a temperature chamber for ~1s). The TL curves from these heated particles were recorded and compared to the TL from control samples, which were not exposed to the temperature profile. A simple TL model (first order TL peaks with a distribution of activation energies and single frequency factor) was applied to determine the temperature experienced by the particles based on their TL curves. The temperatures indicated by the TL particles were comparable to the temperatures measured using thermocouples, with some exceptions. These exceptions include situations in which the material was not suitable for a specific temperature range (e.g., CSO heated below 200°C for 2h duration) or in which particle aggregation prevented the aliquots from being uniformly heated (e.g. LBO heated in the temperature chamber).

Physical properties of petroleum formed during maturation of Lower Cambrian shale in the upper Yangtze Platform, South China, as inferred from PhaseKinetics modelling

Lower Cambrian shale in the Upper Yangtze Platform (UYP), South China, is an important source rock of many conventional petroleum fields and was recently recognized as a promising unconventional shale reservoir. In this paper, hydrocarbon generation kinetics and petroleum physical properties were investigated using the PhaseKinetics approach (di Primio and Horsfield, 2006) and a Cambrian shale sample from the Georgina Basin, North Territory Australia (NTA), as similar paleogeological and sedimentary environments in Cambrian are found for the UYP and NTA.The source rock comprises type II kerogen and belongs to an organofacies generating Paraffinic–Naphthenic–Aromatic low wax oil. Bulk petroleum generation can be described by a single frequency factor A = 8.43E + 14 (1/s) and a dominant activation energy at 56 kcal/mol, which is characteristic for sulphur-poor organic matter deposited in an anoxic marine environment. Onset (transformation ratio TR = 10%) and end (TR = 90%) of bulk hydrocarbon generation was calculated to take place at 120 °C and 165 °C respectively for an assumed average geological heating rate of 1.5°C/Ma. Based on the thermal history of a local “model”-well, onset temperature was not reached until the Middle Triassic (241 ma) when sediments were buried more than 2000 m and basalt eruptions caused enhanced heat flows. The main generation stage of primary petroleum took place during the Middle–Late Triassic and ended in the Early Jurassic (187 ma) for burial depths exceeding 4000 m (TR 90%; 165 °C). Temperatures increased to more than 200 °C in the Middle–Late Jurassic leading to secondary cracking of primary products.Hydrocarbons formed at the onset (TR = 10%) of petroleum generation can be characterized by a gas-oil-ratio (GOR) of 63 Sm3/Sm3, a saturation pressure (Psat) of 101 bar, and a formation volume factor (Bo) of 1.2 m3/Sm3. Those parameters stay low during primary petroleum generation before 203 ma, at temperatures < 145 °C, and at burial depths <3400 m (GOR = 176 Sm3/Sm3, Psat = 189 bar, Bo = 1.6 m3/Sm3 at 90% TR). However, predicted parameters increase rapidly (GORs >> 10,000 Sm3/Sm3, Psat > 250 bar and Bo > 2.0 m3/Sm3) during secondary cracking starting roughly at 200 ma, 152 °C and 3500 m burial. Assuming zero expulsion, the shale reservoir position within the sedimentary basin indicates that bubble point pressure was always below reservoir pressure, and fluids in the shale reservoir occurred only as a single, undersaturated phase throughout maturation history. Black oil and volatile oil phases dominated during the primary cracking period, whereas wet gas and dry gas phases dominated during the secondary cracking period.

Kinetic simulation of hydrocarbon generation from lacustrine type I kerogen from the Songliao Basin: Model comparison and geological application

Eight lacustrine Type I kerogen samples from the Songliao Basin were pyrolyzed using the Rock-Eval equipment, and parallel first-order reaction models including the model with a single frequency factor and a discrete distribution of activation energies (SFF model) and the model with multiple frequency factors and a discrete distribution of activation energies (MFF model) were adopted to analyze kinetic characteristics of hydrocarbon generation of the Type I kerogen samples. The results show that the MFF and SFF models can satisfactory simulate hydrocarbon generation under laboratory conditions and the Type I kerogen shows relatively concentrated activation energy distributions (activation energies of MFF model range from 190 kJ/mol to 250 kJ/mol, activation energies of SFF model range from 220 kJ/mol to 240 kJ/mol), which indicates a homogeneous chemical bond structure of the Type I kerogen. The hydrocarbon generated curves from Type I kerogen were calculated by using the two models with a linear heating rate (3.3 K/Ma). It indicates that the hydrocarbon generation potentials (reaction fractions) are underestimated by using the SFF model during the kerogen thermal degradation for the components with chemical bond of lower and higher activation energies, while this problem can be avoided by using the MFF model. The calculated temperatures for 50% transformation ratio (TR) of all samples differ by as much as 20 °C. For the SFF model, the hydrocarbon generation curve obtained by using the weighted averaged kinetic parameters and the SFF model almost includes every curve calculated by using its own kinetic parameters. While the curve obtained by using the weighted averaged kinetic parameters and the MFF model cannot include every curve for all samples, it lies at the position of the averaged curve of all samples. The application of the MFF model in Songliao Basin shows that if TR 10% is taken as the onset of hydrocarbon generation, the threshold depth of hydrocarbon generation is about 1700 m, which is consistent with other geochemical parameters, such as S 1/TOC, S 1/(S 1 + S 2) and HC/TOC.

Hydrocarbon Generation Kinetic Characteristics from Different Types of Organic Matter

Abstract:In order to contrast the hydrocarbon generation kinetic characteristics from different types of organic matter (OM), 18 samples from different basins were pyrolyzed using Rock‐Eval‐II apparatus under the open system. From the experimental results, the curve of hydrocarbon generation rate vs. temperature can be easily obtained, which usually can be used to optimize kinetic parameters (A, E, F) of the hydrocarbon generation model. In this paper, the parallel first‐order reaction with a single frequency factor model is selected to describe the hydrocarbon generation kinetic characteristics. The hydrocarbon generation kinetic parameters reveal that the types of compound structures and chemical bonds of the lacustrine facies type I OM are relatively homogeneous, with one dominating activation energy. The types of chemical bonds of the lacustrine facies type II2 OM and the terrestrial facies type III OM are relative complex, with a broad activation energy distribution, and the reaction fraction of the preponderant activation energy drops with the decrease of hydrogen index. The impact of the activation energy distribution spaces on the geological extrapolation of kinetic parameters is also investigated. The results show that it has little effect on the hydrocarbon transformation ratio (TR) and therefore, the parallel first‐order reaction model with proper number of activation energies can be better used to describe the hydrocarbon generation process. The geological extrapolation results of 18 samples of kinetic parameters show that the distribution range of the hydrocarbon generation rate of the type I OM is relatively narrow and the hydrocarbon generation curve is smooth. In comparison, the distribution range of the hydrocarbon generation for type II1 and type II2–III OM are quite wide, and the hydrocarbon generation curves have fluctuation phenomena. The distribution range of the hydrocarbon generation rate and the fluctuation phenomena are related to the kinetic parameters of OM; the narrower the activation energy distribution, the narrower the hydrocarbon generation rate distribution, and the smoother the hydrocarbon generation curve, and vice versa.

Modelling petroleum formation from heterogeneous source rocks: the influence of frequency factors on activation energy distribution and geological prediction

The application of basin modelling programs permits the prediction of organic matter transformation to oil and gas under variable geological conditions. Simplified kinetic models are commonly applied with a distribution of activation energies and a single average frequency factor. Here it will be shown that such simplified kinetic models are not sufficient to correctly predict organic matter transformation in heterogeneous kerogens under geological conditions. In the present paper, individual pairs of frequency factors and activation energies were calculated from the temperature shift of nine different levels of organic matter transformation ranging from 0.1 to 0.9 TR at different heating rates (0.1, 0.7 and 5.0 K/min). This type of extended kinetic evaluation has been applied on samples from the Green River Shale, the Toarcian Shale, the Duvernay Formation, the Draupne Formation, a type II-S source rock, petroleum asphaltenes, and a Tertiary coal from the Mackenzie Delta, respectively. For terrestrial and heterogeneous marine source rocks the frequency factors systematically increase with increasing level of transformation, while such an increase was insignificant or absent when homogeneous source rocks were studied. By applying geological heating rates it was possible to illustrate the significance of the extended calculation of individual frequency factors. The predicted onset temperature of petroleum formation was displaced to 60–70 °C in case of lignites/coals and type II-S source rocks, which was up to 30–40 °C lower than predicted by the use of a conventional single frequency factor model. To a lesser extend such a shift was also documented for some marine shales (e.g. Draupne Formation and the Duvernay Formation). The reason for this phenomenon is that an average single frequency factor suppresses the initial formation of petroleum at geological heating rates because high activation energies are needed to maintain the kinetic equation at low generation temperatures. In contrast, correct activation energies derive from individual frequency factors which keep the activation energies low at low levels of organic matter transformation and result in a more reliable description of the low energy bonds in the heterogeneous organic matter types.

A spreadsheet program to optimize kinetic parameters of organic matter from laboratory pyrolysis data

Transformation of sedimentary organic matter (OM) to hydrocarbons is best modeled by assuming the total reaction suite consists of parallel degradations of ‘i’ hypothetical components following the Arrhenius equation and first order kinetics. A kerogen can be defined by characterizing each constituent component by its activation energy ( Ei) their initial potentials (Xios) and a single frequency factor ( A). We present a user friendly Lotus 1-2-3 program to determine A, Ei and Xio distribution of OMs using a multiple linear regression utility and programmed macros. Rock Eval (RE) S 2 curves of three heating rates are required. Equally spaced time/temperature and peak height data for S 2 curves of ‘ n’ temperature steps in increasing order of heating rates are the inputs for the program. The fraction of hydrocarbon generated ( f) from 19 hypothetical components of Ei 30, 32,34…78 Kcal/mole for ‘ n’ temperature/time steps, by using frequency factor ( A) value and assuming Xios=1, are calculated and set up in a ‘ n×19’ matrix (matrix M). The fraction of total hydrocarbon generated ( f) at ‘ n’ temperature steps, obtained from the observed peak heights, are set up in a ‘ n×1’ matrix (matrix L). Matrix M is suitably reduced by the program to ‘ n× k’ matrix (matrix N) where ‘ k’ is a variable, facilitating matrix inversion. Regressing matrix N against matrix L by the program, gives the Xios for ‘ k’ Ei components along with a standard error (ERR) of Y estimates and R 2. Xios and A are then optimized iteratively by varying A values and selecting the solution associated with the lowest ERR value. Results of applying the program on data sets of two widely different types of samples from Indian basins are shown. They match the results obtained from the more sophisticated proprietary software.

Using natural maturation series to evaluate the utility of parallel reaction kinetics models: an investigation of Toarcian shales and Carboniferous coals, Germany

Open-system pyrolysis is routinely performed on immature samples in order to determine the kinetic parameters of petroleum generation at both bulk and molecular levels. This study tested such predictions for Type II and Type III organic matter by making calibrations with both artificial and natural maturity sequences of Toarcian shales (Posidonia shale; 0.48–1.44% R r) and Carboniferous vitrains (0.74–2.81% R r). Both natural series showed little or no compositional variability attributable to kerogen type. Artificially matured samples were prepared by non-isothermal heating (0.7 K/min) of the least mature samples up to end temperatures between 375 and 470°C under either closed- or open-system conditions. Measured generation rate versus temperature curves were analyzed assuming a distributed system of activation energies and a single frequency factor in each case. The resulting kinetic parameters were then used to assess bulk petroleum formation rates for geological heating conditions. In the case of all artificially matured samples, measured and predicted bulk petroleum formation rate vs. temperature curves for each maturation stage remain within the original envelope defined by the least mature sample, despite an upward shift of T max temperatures. This confirms that the reactions taking place during both the pyrolysis measurements and simulated maturation processes are the same, involving mainly homolytic cracking. A similar pattern of measured and predicted rate curves is reproduced by the natural maturation sequence of the Toarcian shales in the maturity range of 0.53 to 1.44% R r suggesting that petroleum generation within these natural systems also results from cracking reactions, and therefore that petroleum generation over geological time can be reliably extrapolated from open-system pyrolysis of the appropriate immature sample. By contrast, significant deviations are observed for the natural coal series, with measured and predicted rate curves extending beyond the immature envelopes. In accordance with the pronounced increase of frequency factors and of protonated aromatic carbon concentrations, this behavior is attributed to solid state aromatization reactions which compete with product generation during natural coalification, but which are not reproducible to the same extent by experimental heating. It is concluded that petroleum generation from vitrinitic coals over geological time cannot be reliably extrapolated from open-system pyrolysis of low rank samples.

A test of the parallel reaction model using kinetic measurements on hydrous pyrolysis residues

Open-system kinetics are measured on extracted residues from hydrous pyrolysis to test aspects of the parallel reaction model and the assumption of a single frequency factor for all energies. The absolute rates of the residues form a series supporting the concept that hydrous pyrolysis removes primarily the more reactive components at lower temperature. The parallel reaction model works well for the marine kerogen, except for the small amount of refractory material in the highest temperature residue that is not represented adequately in kinetics from the initial sample because of measurement limitations. The kinetic parameters derived from the unreacted coal do not work as well and predict too much remaining reactive material. The discrepancy may be caused by a weakness in the parallel reaction model, or due to the fact that the open-system kinetics are not intended to predict the generation and subsequent removal of extractable organic matter. That the parallel reaction model works less well for coal confirms earlier concerns about the complexity of oxygen-related reactions. The constant frequency factor approximation works fairly well for the kerogen but marginally well for the coal. The frequency factor shifts about ten-fold over the activation energy range in the kerogen and about 100-fold over the activation energy range in the coals.

Compositional information for kinetic modelling and petroleum type prediction

The process of petroleum generation can be described in terms of timing and quantity by kinetic modelling. Compositional changes which occur during maturation are usually not taken into account in these models, despite the fact that they play an important role in defining physical behaviour of the petroleum under changing subsurface conditions. With this in mind, both open and closed system pyrolysis methods were applied to a set of immature Posidonia Shale samples from the Lower Saxony Basin (NW Germany) for studying both qualitative and quantitative aspects of the petroleum generation process. With the open system non-isothermal pyrolysis method, discrete distributions of activation energies in the range of 47–53 kcal/mol and one single frequency factor were determined. A maturity sequence was established by pyrolysing aliquots of immature Posidonia Shale samples under closed system conditions for various times and temperatures. The compositional changes and the kinetics of formation of single compounds and groups in the C 1–C 35 range were then studied quantitatively using gas chromatography. The sequence was characterised by a progressive increase in both gas/oil ratio (GOR) and paraffinicity. There was only minor variation of the chain length distribution of n-alkanes, indicating a limited pool of precursors in the Posidonia Shale kerogen. Different kinds of single reaction models were used to determine the kinetic parameters for n-alkane generation. A satisfactory fit to the experimental data could not be obtained with first-order kinetics. A good fit could be made using a kinetic model of autocatalytic reactions.

Ionic reorientations and phase transition in solid IF6AsF6

19F static and rotating frame spin–lattice relaxation times (T1 and T1ρ) as well as broadline NMR studies have been carried out on solid IF6AsF6 between 213 and 393 K. From the T1– and T1ρ–temperature behaviour, we inferred a phase transition at 350(± 2) K and a supercooled high temperature phase. In both phases the second moments are consistent with a model where both IF6+ and AsF6− reorient about random axes. The T1 and T1ρ data in the low temperature phase can be interpreted in terms of a single frequency factor τ0 = 3.15(± 0.2) × 10−16 s and activation energy Ea = 10.4(± 0.4) kcal/mol for both cation and anion reorientation. At the temperature of the phase transition the ionic-reorientational frequencies become faster by ~ 2 orders of magnitude. In the high temperature phase T1 and T1ρ are essentially independent of temperature which may be associated with a spin–rotation relaxation mechanism.