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The main controls on petroleum accumulations in sedimentary basins include source rock distribution, thermal maturity, migration pathways, as well as structural and stratigraphic traps. While shale plays and conventional reservoirs are endmembers governed by contrasted geological processes, unconventional hybrid systems represent a continuum between them and share common characteristics with both. The Montney Formation provides a well-documented example of such a play, where petroleum distribution is controlled by a combination of downdip increase of thermal maturity, fluid migration influenced by lateral and vertical permeability variations, and pressure compartmentalization. In this paper, we integrate publicly available data from thousands of wells within a well-defined stratigraphic framework, to illustrate these regional and local controls on petroleum distribution in the Montney hybrid play. We demonstrate that produced gas compositional mapping is a powerful tool that complements comparatively sparse data from core or cuttings-based organic geochemistry and petrography methods, to provide an unparalleled level of detail of petroleum distribution at various scales. Coupling this compositional mapping with reservoir pressure data and published faults reveals a strong control of the structural framework on petroleum migration routes. The main targets of horizontal drilling in the Montney play are carrier beds that were charged by up-dip migrating petroleum and experienced further thermal maturation during the burial history. The relative contribution of different source rocks to this petroleum system remains speculative and further investigation is needed to solve this conundrum.

The principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry, numerical modeling of oil biodegradation in reservoirs, and analysis of oil property data sets from a variety of geological settings. Petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80C. In most reservoirs with low concentrations of aqueous sulfate, methanogenic degradation is a primary mechanism of petroleum degradation, whereas in waters containing abundant sulfate, sulfate reduction and sulfide production may dominate. Net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature, the chemical compounds being degraded, and relationships between the oil-water contact (OWC) area and oil volume. The relative volumes of water leg to oil leg, prior level of oil biodegradation, and reservoir water salinity act as second-order controls on the process. Typically, degradation fluxes (kilograms of petroleum destroyed per square meter of oil-water contact area per year or kg petroleum m2 OWC yr1) for fresh petroleum in clastic reservoirs are in the range of 103–104 kg petroleum m2 OWC yr1 and increase with decreasing reservoir temperature, from zero near 80C, to a maximum flux at the OWC of less than 103 kg petroleum m2 OWC yr1 at a temperature less than 40C. At very low reservoir temperatures and with severely degraded oils, such as are seen in the near-surface Canadian tar sands at the present day, the net degradation fluxes are much less than maximum values. Nutrient supply from the aquifer and adjacent shales, mostly buffered by mineral dissolution, probably provides the ultimate control on the range of degradation flux values. Oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude-oil biodegradation. Continuous vertical gradients in the oil columns document episodic degradation for many millions of years, suggesting that the time scales of oil-field degradation and petroleum charging are similar. The flux-temperature relationship we have derived, coupled with typical reservoir charge histories, defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge, mixing of biodegraded and fresh oils, and reservoir-temperature history as the primary controls on fluid properties. These flux-temperature relationships are easily integrated into prospect charge modeling procedures; sensitivity analyses show that the limiting factor in fluid property predictions, using even this first-level approach, are ultimately constrained by the accuracy of current oil-charge modeling estimates. The absence today of any functional geochemical proxies for assessing oil-residence time in oil fields and the substantial uncertainty in petroleum-charging times estimated by forward basin modeling is a major obstacle to more accurate fluid-property predictions that needs to be addressed.

The Ordovician Trenton Group (Sherman Fall and Cobourg formations) and the Lindsay (Collingwood Member) and Blue Mountain formations of southwestern Ontario were examined using Rock-Eval pyrolysis, gas chromatography, gas chromatography-mass spectrometry, and incident-light microscopy to evaluate their paleodepositional environments, thermal maturities, and source rock potential. All units contain sufficient amount of oil-prone (type II), predominantly marine organic matter to be considered as petroleum source rocks. Unstructured bituminite with varying proportions of unicellular alginite are the dominant dispersed organic matter macerals. The bituminite typically occurs in massive to laminated, granular or patchy populations that commonly show microtextural relationships. Persistent inclusions of Leiosphaeridia telalganite demonstrate that planktonic algal debris was a primary organic substrate for blooming microbes. Disseminated coccoidal Gloeocapsomorpha prisca is found in minor amounts, usually in association with common to abundant acritarchs. Zooclasts (chitinozoa, graptolites, scolecodonts) and solid bitumen also are present as maceral inclusions within the bituminite network. The biomarker distributions for all of the studied units are those expected for marine organic matter deposited in a clastic-dominated environment. The extracts are characterized by a smooth n-alkane profile, with low abundance of C20+ members, typical for marine derived organic matter. Pristane/phytane ratios range from 0.97 to 1.72, indicating dysoxic conditions during deposition. Smooth C31-C35 homohopane profiles, Ts/Tm ratios (typically above 1.0), and a higher concentration of diasteranes relative to regular steranes all appear to indicate the clay-bearing character of these rocks. The predominance of C30 hopane over C29 regular sterane is interpreted to reflect a primary microbial input and extensive reworking of the organic matter. Optical (reflectance, fluorescence) and geochemical (Tmax, biomarker data) thermal maturity parameters indicate that the Trenton and Blue Mountain strata are within the zone of prolific oil generation throughout the whole area of study. The Collingwood shales are mature with respect to petroleum generation in the eastern part (Toronto area) and only marginally mature in the northern part (Georgian Bay area) of the study area. In general, the biomarker composition of the extracts from all examined units is compatible with that of the oils found in the Trenton reservoirs of southwestern Ontario; however, geochemical and geological evidence suggests that the organic-rich shaly laminae within the Trenton Group are the principal source of these oils. Accumulation of organic carbon in the Ordovician sediments of southern Ontario is suggested to derive from low-energy, normal-marine environments grading from shallow-shelf into deep-shelf and open-basinal settings. The nutrient availability and, consequently, higher bioproductivity, more intense consumption of oxygen, and progressing anoxia, controlled by a low-latitude location, diminished water circulation, stratification of the water column, and a depressed pycnocline resulted in high preservation rates. The amorphous nature of kerogen reflects significant microbial interaction at the water/ sediment interface and within the sediments where reducing conditions must have periodically predominated.