Vitrinite model

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

H/C = atomic hydrogen-to-carbon ratio V = vitrinite content of coal VM volatile matter St = total sulfur TRM = total reactive macerals The adequacies of these reactivity correlations, expressed as a percentage of the total variation in the data set explained by the model, were 80.0%, 79.2%, and 47.5% respectively. A later paper in the series (21) concentrated on the development of reactivity correlations for a set of 26 high volatile bituminous coals with high sulfur contents, and extended the models previously developed in include analyses of the liquefaction products and coal structural features. These structural features included the usual... 

The above models are representative of the active macerals, particularly vitrinite. Inert macerals, such as fusinite and micrinite, are believed to have large aromatic planar structures with fewer substituents (14) and behave similar to chars. 

There has been available (or some years unarguable evidence that each of the major macerals groups has a distinct set of structural characteristics, and that the major macerals in any one coal do differ materially in chemical structure from each other. We must therefore admit that chemical structures alleged to represent whole coals are futile, and that basic chemical research should use single macerals in as pure a state as possible. On the other hand, some believe that pure vitrinite macerals at least can be represented usefully by a model structure. 

Hatcher P. G. (1990) Chemical structural models for coalified wood (vitrinite) in lowrankcoal. Org. Geochem. 16,959-968. 

Table 5.5 Activation energy distribution for kinetic modelling of vitrinite reflectance (EASY%Ro A= 1013s 1 after Burnham Sweeney 1989 Sweeney Burnham 1990)...

Calibration of the thermal model is possible using present-day bottom-hole temperatures from exploration wells (Deming Chapman 1989) and by the comparison of modelled and measured vitrinite reflectance (see Section 5.7.3), an example of which is shown in Fig. 5.50. There are other measurements that can provide time-temperature constraints, such as fission-track analysis (Naeser 1993 Gleadow Brown 1999), homogenization temperatures of fluid inclusions (Roedder 1984) and clay transformations (Hoffman Hower 1979). 

Fig. 5.51 Kerogen transformation at a constant heating rate of3°CMyr 1, based on single A plus discrete Eact distributions (after Tegelaar Noble 1994) for tasmanites (type I, Cretaceous, North Slope, Alaska), Monterey shale (type II—S, Miocene, Ventura, California), Kimmeridge Clay (type II, Jurassic, North Sea) andManville Formation (type III, Cretaceous, Alberta). Modelled vitrinite reflectance based on EASY%Ro (after Sweeney Burnham 1990 Table 5.5).

Hatcher P.G. (1990) Chemical structural models for coalified wood (vitrinite) in low rank coal. Org. Geochem. 16, 959-68. Hatcher P.G., Clifford D.J. (1997) The organic geochemistry of coal from plant materials to coal. Org. Geochem. 21, 251-74. 

Hatcher P.G., FaulonJ.-R,Wenzel K.A., Cody G.D. (1992) A structural model for lignin-derived vitrinite from high-volatile bituminous coal (coalified wood). Energy Fuels 6, 813-20. 

Sweeney J.J., Burnham A.K. (1990) Evaluation of a simple model of vitrinite reflectance based on chemical kinetics. Am.Assoc. Pet. Geol.Bull. 74, 1559—70. 

Structure 5. Proposed model structure of vitrinite-rich bituminous coal containing —83-84% carbon. A star (it) indicates where polymerization might occur. (Adapted from references 75 and 76.)... 

Three 2D lines crossing the main kitchen areas were modelled in this study. The models were calibrated to data from eight wells, consisting of measured vitrinite reflectance, corrected well temperatures and pore pressure. 

Kamp PJJ, Webster KS, Nathan S (1996) Thermal history analysis by integrated modelling of apatite fission track and vitrinite reflectance data Application of an inverted basin (Bnller Coalfield, New Zealand). Basin Res 8 383-402... 

Silica concentrations in pore waters particularly and also in other subsurface and surface waters were determined in dozens of samples as part of this study, using atomic absorption spectrophotometry as well as inductive coupled plasma. This was essential for silica budget estimations. Present-day and paleothermal profiles were obtained from measured temperatures in boreholes, vitrinite reflectance (Rq) in interlayered-with-sandstones shales and from basins thermal modeling. 

A general model of the diagenesis of the sandy reservoirs of the Sahara is presented in Fig. 4.17. The sequence of the diagenetic stages is controlled by temperature and time. Vitrinite reflectance in shales adjacent to or intercalated with the quartz sandstones indicates their exposition in time and space to temperature and may be used also as an indicator of the thermal maturity of the quartz sandstones. In this way the vitrinite reflectances correspond to the stage of mesodiagenesis. Mechanical compaction dur-... 

The input parameters for the model include the present-day sedimentary cross section, estimates of the amplitude and rate of erosion, the lithological composition and petrophysical characteristics of rocks, the structure of the lithosphere (basement) and its rock parameters, paleotemperature markers (vitrinite reflectance), paleoclimate, sea paleodepths, present-day surface heat flow, depth-temperature profiles, and information on the paleotectonics and the present-day tectonic setting of the basin. The evolution of the Oued el-Mya Basin is used to demonstrate the model. Table 6.1 presents the basin s main stages of evolution, which include sedimentation, hiatus, and erosion. 

Temperatures within the sedimentary section calculated as a fimction of time are used to estimate the maturation level of the organic matter. The kinetic model of vitrinite maturation (Sweeney and Burnham 1990) is the primary method of maturity estimation. Comparison of measured vitrinite reflectance Rg) with the calculated values and present-day temperature profile (Fig. 6.6) is used to control modeling parameters. The time-temperature index (TTI) (Lopatin 1971 Waples 1980) is also computed as a simple method to describe the paleothermal regime. 

The thermal and burial histories of the basin for a variant that is free from erosion in the Permian were simulated for comparison with the main model (Fig. 6.7). This variant was controlled by present-day temperatures and vitrinite reflectance (similar to Fig. 6.6) and, by coincidence of the tectonic curve, calculated by removing the sediment and water load, resulting from variation in the thermal state of the basement (as... 

Dykstra J (1987) Compaction correction for burial history curves applications to Lopatin s method for source rock maturation determination. Geobyte 2(4) i6-z3 Espitalie J (1986) Use of as maturation index for different types of organic matter. Comparison with vitrinite reflectance. Therm. Model. Sediment. Basins. 1st IFP Explor. Res. Conf. Carcans. June 3-7, Paris, p 475-496... 

Burnham A. K. and Sweeney J. J. (1989) A chemical kinetic model of vitrinite maturation and reflectance. Geochim. Cosmochim. Acta 53, 2649-2657. 

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