Monterey Shale

Desulfurisation of polar fractions of relative immature oils and sediment from hypersaline palaeoenvironments yields n-alkanes with strong even-over-odd carbon number predominances (20,42 e.g., Figure 11). This phenomenon is, however, not restricted to samples from hypersaline palaeoenvironments (e.g., Jurf ed Darawish Oil Shale, Monterey Shale). 

A large variation in the distribution patterns of C20 isoprenoid thiophenes has been encountered upon analysis of sediments and oils ranging from normal marine saline to hypersaline (16). Figure 8 shows that in samples representing a normal marine salinity environment (Monterey Shale-Naples and -El Capitan Beach, Jurf ed Darawish-45) isoprenoid thiophenes VI and VII are dominant whereas in samples from hypersaline palaeoenvironments (Sicily seep oil-E2, Rozel Point oil) isoprenoid thiophene V and the so-called midchain isoprenoid thiophenes (I-IV) are relatively abundant. C20 isoprenoid bithiophenes (VIII-X) only occur when the midchain isoprenoid thiophenes are relatively abundant (Figure 9). 

Table I. Major alkylthiophenes identified in pyrolysates of the Jurf ed Darawish Oil Shale and Monterey kerogens and asphaltenesa...

Two Type II-S kerogens (as defined by Orr (i)) from the onshore Santa Maria Basin Monterey formation were pyrolyzed in this study to determine (a) the distribution of sulfur and its isotopic composition among the various products formed during artificial maturation, and (b) maturation trends reflected in the sulfur isotopic and elemental S/C ratios of kerogens, and in the variation of C and H isotopes. In addition, S isotopes in pyrites, kerogens and bitumens from the two Monterey shale samples were examined to speculate on the mode of S incorporation into Santa Maria Basin sediments. 

Table I. Characteristic of Two Monterey Formation Shale Samples Used in the Pyrolysis Experiments...

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).

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... 

Nelson B. C., Eglinton T. L, Seewaud J. F., Vairavamurthy M. A. and Miknis F. P. (1995) Transformations in organic sulfur speciation during maturation of Monterey shale eonstraints from laboratory experiments. In Geochemical Transformation of Sedimentary Sulfur eds.NL A. Vairavamurthy andM. A. A. Schoonen), Vol. 612, pp. 138-166. American Chemical Society Symposium Series, ACS, Washington, DC. 

Because of the high CPI in our sample, we believe that the measured value we obtained (— 25.75%o) reflects a contribution of terrestrial vegetation. In addition, the lower isotope value of the protokerogen, aromatic and the aliphatic hydrocarbons relative to bulk carbon may also imply contribution from Monterey shale and petroleum in addition to that from land plants. ScHOUTEN (1995) found that the average for n-alkanes ranging from C24 to C33 in the... 

Monterey Shale varied from------28 to —32%o. Similar isotopically light alkanes have also been... 

These treatments were conducted in naturally fractured Monterey shale. Based on DST results, formation damage was suspected. Evaluation of previously unsuccessful acid jobs in the same zones, drilling records, workover data, and laboratory testing suggested that formation damage was due to one or more of the following ... 

Table A-11, Bullheaded mud damage removal In naturally fractured formations (e.j Monterey shale)...

Table 1. Dissolved inorganic species released from a sample of Monterey Shale (MR-216) into the surrounding water after heating for 72 h at 330 °C in 1-1 reactors with different surface compositions. Concentrations are given in mg/l and were determined by A A or ICP-AES... 

Fig. 5. Weight percent of original organic matter converted to aqueous C2-C5 mono-carboxylic acids after hydrous pyrolysis of aliquots of Kreyenhagen, Monterey, and Phosphoria Retort shales isothermally heated at temperatures from 240 to 365 for 72-h durations. Experiments were conducted in carburized stainless steel-316 reactors in the authors laboratory...

Fig. 9. Arrhenius plot for acetic acid generation from hydrous pyrolysis experiments conducted on the Monterey and Phosphoria Retort shale (Fig. 5). Calculated activation energies ) and frequency factors A ) assume a first-order rate law...

Fig. 11. Plots of expelled immiscible oil and aqueous C2-C5 monocarboxylic acids generated through a series of isothermal hydrous pyrolysis experiments conducted on aliquots of Monterey and Phosphoria Retort shales...

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