ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉This work presents results from an ongoing laboratory study investigating pore network characteristics and matrix permeability of selected intervals within the Montney Formation (Western Canada). The primary objectives are to: 1) compare different laboratory-based methodologies for determination of porosity and matrix permeability; 2) characterize the pore network attributes (porosity, pore size distribution (PSD), dominant pore throat size, specific surface area) and matrix permeability of the selected target intervals; and 3) analyse the effects of different controlling factors (anisotropy, effective stress, bitumen saturation) on matrix permeability. Eight selected pairs of core plugs, drilled vertically and horizontally, are analysed in this study. These core plugs are obtained from a vertical interval of 15 m within the fine-grained intervals of the Upper Montney Formation in British Columbia (Canada). The experimental techniques used for characterization include: bitumen reflectance (BR〈sub〉o〈/sub〉); RockEval pyrolysis; helium pycnometry; Archimedes, caliper and 3D laser scanner analyses; low-pressure gas (N〈sub〉2〈/sub〉) adsorption; pulse-decay; and crushed-rock gas (N〈sub〉2〈/sub〉, He) permeability measurements.Excluding one of the samples (a laminated vertical core plug): 1) the slipcorrected pulse-decay gas (N〈sub〉2〈/sub〉) permeability values (measured at effective stress of 15.8 MPa) and apparent crushed-rock gas (He) permeability values generally increase with increasing porosity (4.2–8.1%), ranging from 1.4·10〈sup〉−〈/sup〉〈sup〉5〈/sup〉 to 8.6·10〈sup〉−〈/sup〉〈sup〉4〈/sup〉 mD: and 2) the slip-corrected pulse-decay (N〈sub〉2〈/sub〉) permeability values (1.2·10〈sup〉−〈/sup〉〈sup〉4〈/sup〉−8.6·10〈sup〉-4〈/sup〉 mD) are consistently higher than apparent crushed-rock (He) permeability values (1.4·10〈sup〉−〈/sup〉〈sup〉5〈/sup〉−1·10〈sup〉-4〈/sup〉 mD). Pulse-decay (N〈sub〉2〈/sub〉) permeability values measured parallel to bedding (horizontal core plugs) are consistently between 10% and 25 times higher than those measured perpendicular to bedding (vertical core plugs). Based on a single pair of laminated core plugs analysed in this study, the degree of permeability anisotropy (ratio between parallel and perpendicular permeability values) appears to be significantly higher for the laminated core plugs (up to 25 times) than bioturbated core plugs (up to 3.5 times). Compared to pulse-decay (N〈sub〉2〈/sub〉) permeability values, there is a minimal discrepancy (considering the maximum experimental error margin) between the crushed-rock gas permeability values that were measured on pairs of horizontal/vertical core plugs after crushing/sieving. In a gross sense, slip-corrected pulse-decay (N〈sub〉2〈/sub〉) permeability values decrease with increasing bitumen saturation.Applying multiple analysis techniques on a selected suite of core plugs and crushed-rock materials derived from them, this study provides: 1) valuable insight into the causes of observed variations in porosity/permeability values obtained from laboratory-based techniques; and 2) an integrated description of pore network characteristics and matrix permeability for selected fine-grained intervals within the Montney Formation.〈/span〉

Description: The organic carbon-and uranium-rich, marine Alum Shale Formation in northwestern Europe (Middle Cambrian (Miaolingian) to Early Ordovician) was deposited in the Baltic Basin and surrounding areas. It is a proven source rock for conventional oil either in sandstones of Cambrian age or Ordovician and Silurian carbonates, and also contains a potential for shale oil and for biogenic or thermogenic shale gas. Despite the absence of higher land plant precursors, the primary Type II kerogen has an abnormally strong aromatic character at low thermal maturities due to α-particle bombardment by the elevated uranium content. The characteristic aromatic kerogen structure results in dead carbon formation and enhances hydrocarbon retention. As a consequence, effective petroleum expulsion is limited during maturation. The petroleum generation properties of the Alum Shale Formation changed over geological time due to the accumulated uranium irradiation. For thermally immature samples, high uranium content is positively correlated with high gas-oil ratios and the aromaticities of both the free hydrocarbons residing in the rock and the pyrolysis products from its kerogen. Such characteristics indicate that irradiation has had a strong influence on the overall organic matter composition and hence on the petroleum potential. At high uranium content, macromolecules are less alkylated than their less irradiated counterparts and oxygen containing-compounds are enriched. However, the kerogen structure was less altered during catagenesis (420–340 Ma bp) than at present, and thus calibration is needed to predict petroleum generation in time and space. In southern central Sweden biogenic methane in the Alum Shale Formation was formed during oil degradation after the Quaternary glaciation following bitumen impregnation generated from local magmatic Carboniferous – Permian intrusions. Consequently, the Alum Shale Formation includes a mixed shale oil/biogenic gas play that resembles the formation of biogenic methane in the Antrim Shale (Michigan Basin, United States). In the Alum Shale Formation, low salinity pore water created a subsurface aqueous environment, which was favourable for microbes that have the potential to form biogenic methane. The ability to generate biogenic methane from samples of the Alum Shale Formation in incubation experiments still exists today. The permeability coefficients of highly mature Alum Shale Formation from Bornholm Island (southern Baltic Sea) cover a broad range from sub-nanodarcy to microdarcy, depending on fluid type (i.e. gas vs. liquid), (in-situ) fluid content, anisotropy, pore pressure and effective stress conditions. In general, the primary high total organic carbon content was not significantly reduced at overmature stages, consistently with the high sorption capacities. The Alum Shale Formation is thus an attractive gas shale candidate from the perspective of gas generation and retention. The strength of the overmature Alum Shale Formation on Bornholm, which is mainly determined by mineral composition, porosity and spatial distribution of the constituents, is relatively low compared to other well-studied shale formations. Based on brittleness estimates, the Alum Shale Formation may be regarded as an unconventional reservoir rock of medium quality from the mechanical point of view.