Rock-Eval analysis

NOTE Tmax parameter from Rock-Eval analysis as defined by Espitalid et al. (75). 

The chemical compositions of oil shales and oil shale kerogen have been studied extensively (20). However, little work has been done to integrate chemical composition data in order to aid in the selection of suitable extracting processes. In this study, five analysis methods were used to chemically characterize the samples. These methods included Rock-Eval analysis, Fischer analysis, Xi C NMR, Ultimate analysis, and X-ray diffraction mineral analysis. 

Table II presents the results of the Rock-Eval analysis. In this table, SI indicates the amount of free hydrocarbons already generated in the shale and S2 indicates the amount of hydrocarbons generated by the decomposition of kerogen at high temperatures.

Espitalie J. and Bordenave M. L. (1993) Screening techniques for source rock evaluation tools for source rock routine analysis Rock-Eval pyrolysis. In Applied Petroleum Geochemistry (ed. M. L. Bordenave). Editions Technip, Paris, France, pp. 237-261. 

Rock-Eval pyrolysis (Espitalie et al., 1977) was applied to immature ancient marine sediments by Herbin and Deroo (1979) and to recent marine sediments by Debyser and Gadel (1981). This technique results in information similar to elemental analysis, but the procedure is much faster, cheaper, and easier. However, it seems necessary to modify this method for use in recent sediments, where organic matter is thermally labile and rich in oxygen. This problem is currently under investigation at the Institut Francais du Petrole. 

Ra = R3 -h (10Rc)/0.9. The RC (residual carbon) term represents heavy bitumens or recycled kerogens not directly volatilized by pyrolysis, but that could be oxidized to CO2 or CO in the separate oxidation step (Lafargue et al. 1997). Flowever, the Kuparuk formation often contains cements, siderite among others, which decompose to CO2 or CO at temperatures reached in the oxidation step of Rock-Eval 6 analysis. Unacceptable variability in RC was observed in pyrolysis of Kuparuk samples, possibly because of decomposition of carbonate minerals. Therefore, a Y coefficient was adopted to correlate Rock-Eval 6 pyrolysis results to petroleum density, where F=(R1+R2)/ (R1 +R2 + R3). 

The authors thank Susan Reynolds, David Shafer, Russ Bone, Dennis Wegener, James Hiekey, Ben Powell, Riek Tharp, Susan Singletary Gordon and Leslie Deal for their assistance in data acquisition or interpretation. The authors especially thank Paul Walker for assistance with Rock-Eval 6 calibration and analysis. The manuscript was improved by reviews by S. Larter and K. Weissenburger. 

The results of open-system pyrolysis (Rock-Eval II) have been used to specify the kinetic parameters controlling maturation. Hydrocarbon yield rates as determined by these experiments are shown in Fig. 6.9a. Both nonlinear optimization technique (Levenberg-Marquardt method Press et al. 1986 Issler and Snowdon 1990) and linear methods are used to determine the values of the reaction parameters Aj, Ej, andX, . This technique minimizes an error function by comparing the hydrocaibon release rates, Sj, calculated by Eq. 6.9 and those rates measured in open-system pyrolysis. An example of the spectrum of activation energies obtained from this analysis is shown in Fig. 6.9b. 

RockEval (also Rock-Eval, RockEval analysis) A rapid analytical method that utilizes pyrolysis to provide a semi-quantitative measure of the relative proportions of hydrogen, carbon and oxygen in bulk sedimentary organic matter. The instrument heats sediment samples to measure the amounts of hydrocarbons and hydrocarbon-like substances that escape at different temperatures from the organic matter contained in the sediment. The unit also calculates the amount of CO2 created during thermal decomposition of the organic matter. The results of Rock-Eval pyrolysis can help to identify the biotic sources of sediment organic matter. 

Figure 5a and Table la contain data for a set of samples taken from a 1500 m thick section of the Monterey shales. The kerogens were isolated (HCl, HCl/HF removal of carbonates and silicates and dilute nitric acid to remove the pyrite) for some of the core samples, but the total rock was used for the Rock Eval T ax determination to estimate maturation levels. The was measured for the extracted bitumen of each sample. The increase in T ax with depth is correlated with maturation indicating that burial of the samples increased their maturation. Two trends are indicated by the values one starts at +15.6 and increases to +17.7%o, and the second from +19.0 to +21.3%o. The data indicate that the bitumen produced at higher level of maturation is enriched with the heavier isotope. The elemental analysis of the bitumen shows that the shallowest (1400 m) sample has —11% S, whereas the deepest at 2490 m... 

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