Abstract Four-dimensional petroleum system models within the Western Canada sedimentary basin were constructed using hydrous pyrolysis (HP) and Rock-Eval (RE) kinetic parameters for six of the major oil-prone source rocks in the basin. These source rocks include the Devonian Duvernay Member of the Woodbend Group; Devonian-Mississippian Exshaw Formation; Triassic Doig Formation; Gordondale Member; Poker Chip A shale, both of the Jurassic Fernie Group; and Ostracod Zone of the Lower Cretaceous Mannville Group. The Mannville Group coals also contributed oil to the oil sands (Higley et al., 2009) but are excluded herein because HP kinetics were used for both models with identical results. The locations of oil migration flowpaths are identical for the HP and RE models, with the exception of an earlier onset of generation and migration shown with the HP model. Both models show that the oil sands are located at focal points of the petroleum migration pathways. The principal differences between the models are the onset and extent of oil generation from the Jurassic Fernie source rocks (Gordondale Member and Poker Chip A shale) at about 85 Ma with the HP model and 65 Ma with the RE model. Earlier oil generation in the HP model is caused by the high sulfur content of the type IIS kerogen in the Jurassic source rocks. The influence of organic sulfur is accounted for in the HP kinetic parameters, but not the RE kinetic parameters. The cumulative volume of oil generated from the source rocks is 678 billion m 3 for the HP model and 444 billion m 3 for the RE model, or 65% of the HP volume. This difference is attributed to early generation from type IIS kerogen that resulted in much larger volumes of thermally mature source rocks for the Jurassic Fernie Group and consequently larger volumes of generated oil. The Gordondale Member in the HP model generated more than 550 times the volume of oil generated by the Gordondale Member in the RE model. The timing and generated volumes are comparable in the RE and HP models for source rocks that contain normal levels of organic sulfur (type II kerogen). The Duvernay is an exception because of the very low sulfur content of its type II kerogen. The result is higher HP kinetic than RE kinetic parameters, with associated greater thermal maturities required for HP than for RE oil generation. Consequently, there is less mature Duvernay source rock in the HP model than the RE model.

Abstract The Upper Cretaceous Milk River Formation in southeastern Alberta and southwestern Saskatchewan has produced more than 2 tcf of dry (>99% methane) microbial gas ( δ 13 C PDB –65 to –71‰) that was internally sourced. Production is from underpressured fine-grained sandstone and siltstone reservoirs, whereas the gas was generated in interbedded organic-bearing mudstones with low organic carbon contents (0.5–1.50%). The formation experienced a shallow burial history (maximum burial, <1.3 km [<0.8 mi]) and cool formation temperatures (<50°C [<122°F]). Petrologic and isotopic studies suggest that methanogenesis began shortly after deposition and continued for at least 20 to 25 m.y. Mercury injection capillary pressure data from the Milk River Formation and the overlying Upper Cretaceous Pakowki Formation, which contains numerous regionally extensive bentonitic claystones, reveal a strong lithologic control on pore apertures and calculated permeabilities. Pore apertures and calculated permeabilities in Milk River mudstones range from 0.0255 to 0.169 μm and less than 0.002 to 0.414 md, respectively, and claystones from the overlying Pakowki Formation have pore apertures from 0.011 to 0.0338 μm and calculated permeabilities of 0.0017 to 0.0065 md. The small pore apertures and low permeabilities indicate that claystones and mudstones served as seals for microbial Milk River gas, thereby permitting gas to accumulate in economic quantities and be preserved for millions of years. Based on the timing of gas generation, the gas system of the Milk River Formation can be considered an ancient microbial gas system, which is one of several ways it differs from that of the Devonian Antrim Shale, Michigan Basin, where microbial gas generation is a geologically young (Pleistocene and younger) phenomenon. The difference in timing of gas generation between the Milk River and Antrim systems implies that gases in the two formations represent end members of a spectrum of microbial gas accumulations in fine-grained rocks, with the Milk River Formation being an excellent example on which to base a paradigm for an ancient microbial gas system.

Abstract: Mappable variations in the metallic ion concentration of late diagenetic carbonate cements at the surface above Velma oil field can be correlated to a qualitative measure of cathodoluminescence (CL). This proposed measure, the carbonate CL index or CCI, compares trace element quencher and activators of CL in carbonates to visual estimates of CL intensity. The late diagenetic aureole at Velma is well developed. In surface sandstone, the aureole contains abundant Fe sulfides and associated ferroan carbonate cement which imparts a dark-reddish-brown color to the rock. The aureole is surrounded by Fe-poor sandstone. Prior studies of the Permian siliciclastic rocks in the near-surface show that changes in Fe and Mn concentrations in carbonate cement result from Eh-pH zonation in the diagenetic aureole across the production area. Fe 2+ and Mn 2+ ions are, respectively, the common quencher and activator of cathodoluminescence (CL) in carbonate minerals. Atomic absorption (AA) analysis shows these trace elements are present over a wide range of concentrations in our samples. Cements with Mn concentration (concentration annotated as [Mn] in units of ppm) greater than [Fe] commonly have bright CL, and those with [Mn] less than [Fe] will have dull orno CL. Comparison of CL quenchers and activator indices ([Fe] alone, [Mn] alone, [Fe]/[Mn]) to visual CL characteristics at Velma shows only fair agreement. Therefore, we apply a new carbonate CL index, CCI = ([Mn]-[Fe])/([Mn]+[Fe]), in an attempt to qualitatively describe the significant CL active trace element composition relative to the subjectively determined visual luminescence character. We find CCI is better than [Fe]/[Mn], [Fe], or [Mn] as a descriptor of CL because it shows a more systematic variation and clearer relationship to CL intensity than the other chemical CL indices. CCI can vary over the range -1 to 0 to +1, dovetailing with major categories of visual descriptors of intensity (non (or no), dull, or bright CL). At CCI of about -1 no luminescence will be observed from the carbonate cement; at CCI of near but less than 0, dull luminescence; and at CCI >0 the cements are brightly luminescent. The general cathodoluminescence pattern observed in the carbonate cements at Velma is related to CCI with dull- or non-luminescent cement (greater [Fe] than [Mn]) over the production area and dull to bright luminescence (less [Fe] than [Mn]) on its flanks. CCI is mostly negative over the production area and zero or positive on its flanks.