Kirk G. Osadetz

Predicting average annual groundwater levels from climatic variables: an empirical model

On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment.

Bakken/Madison petroleum systems in the Canadian Williston Basin. Part 2: molecular markers diagnostic of Bakken and Lodgepole source rocks

Abstract The uppermost Devonian-Mississippian Bakken Formation black shale and the Mississippian Lodgepole Formation carbonate represent two of the most important source rocks in the Canadian Williston Basin. Quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units. Among others, the Bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria Chlorobiaceae. In contrast, the Lodgepole carbonates at similar maturity levels display a C35 homohopane prominence and abundant benzohopanes, ring-D monoaromatic 8,14-secohopanes and a tetracyclic monoaromatic hydrocarbon. The distinctive nature of molecular marker “fingerprints” diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments. Additionally, the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional, saturate-based biomarker approaches were used for oil-oil and oil-source correlation.

Thermal history of Canadian Williston basin from apatite fission-track thermochronology—implications for petroleum systems and geodynamic history

Abstract Apatite fission track (AFT) thermochronology has been applied to a composite depth profile of Precambrian basement rocks underlying the Phanerozoic Canadian Williston Basin. Thermal histories derived from the AFT data record cycles of heating and cooling which follow the pattern of regional burial history, but which also indicate major temporal and geographic variations in the timing and degree of maximum Phanerozoic temperatures. These variations in the thermal history were not previously recognised from organic maturity indicators and subsidence models. Specifically, our study suggests a late Paleozoic heat flow anomaly with a geographic extent closer to that of Middle Devonian–Carboniferous Kaskaskia subsidence patterns than to that of the Williston Basin proper. This thermal anomaly has both economic and geodynamic significance. The recognition that potential Upper Cambrian–Lower Ordovician petroleum source rocks became fully mature during the late Paleozoic distinguishes that petroleum system from others that entered the main hydrocarbon generation stage in latest Cretaceous and Paleogene time. The late Paleozoic heat flow anomaly suggested from the AFT data implies a geodynamic coupling between inelastic Kaskaskia subsidence and previously inferred late Paleozoic lithospheric weakening. While the temporally varying heat flow model is preferred, the lack of independent constraints on the maximum thickness of upper Paleozoic strata precludes the outright rejection of the previous constant heat flow model. The AFT data provide important new constraints on the evolution of the epicratonic Williston Basin and its geodynamic models.

A Two-Dimensional Regional Basin Model of Williston Basin Hydrocarbon Systems

Institut Francais du Petroles two-dimensional model, temispack, is used to discuss the functioning of petroleum systems in the Williston basin along a 330-km-long section, focusing on four regional source intervals: Ordovician Yeoman formation, Lower Devonian Winnipegosis Formation, Upper DevonianuLower Mississippian Bakken Formation, and Mississippian Lodgepole formation. Thermal history calibration against present temperature and source rock maturity profiles suggests that the Williston basin can be divided into a region of constant heat flow of about 55 mW/m2 away from the Nesson anticline, and a region of higher heat flow and enhanced thermal maturity in the vicinity of the Nesson anticline. Original kinetic parameters used in the calibration were derived or each of the four source rocks from Rock-Eval yield curves. Bakken overpressures are entirely due to oil generation, not compaction disequilibrium. Very low Bakken vertical permeabilities range from 0.01 to 0.001 nd are matched against observed overpressures, whereas Bakken porosities based on the model and confirmed by measurements are inferred to be also unusually low, around 3%. Mature Bakken shales do not seem to have reached hydraulic fractionation thresholds, except perhaps locally in regions of extensional tectonic stress. Hydraulic fracturing cannot be viewed as a pervasive mechanism driving Bakken oil expulsion. Our expulsion model confirms the high residual Bakken oil saturations and explains the low residual S1/TOC by the low Bakken shale porosities. Approximately 85% of the oil generated in the Bakken shales is predicted to have been expelled out of Bakken strata, which agrees with observed S1/TOC trends. Madison Group accumulations at the subcrop edge are found to be fed by Lodgepole-sourced oil only, in particular by the rich middle Lodgepole interval. These accumulations probably result from a three-dimensional migration pattern. Madison accumulations in the Nesson anticline are found to be fed mostly by Lodgepole-sourced oil mixed with minor amounts of Bakken-sourced oil. The vast majority of the expelled Bakken oils are lost in the Madison Group at very low saturations. This explains the low conventional oil resource associated with Bakken sources by recent geochemical studies. Expulsion and migration occurred no earlier than the atest Cretaceous-Paleocene in the Yeoman and no earlier than the Eocene in other source rocks, consistent with temporal controls on oil migration. Flow models show no restriction to expulsion and migration of Yeoman oil. This suggests a potential undiscovered oil resource in Ordovician and Silurian strata of Williston basin, northeast of the Nesson anticline.

Gas hydrate distribution and volume in Canada

Gas hydrate, a solid form of natural gas and water, is inferred to widely occur in Canadian polar and continental shelf regions and in sediment of outer continental margins. Although direct indications of hydrate are few and widely separated, conditions potentially favorable for gas hydrate formation and stability, especially low to moderate temperatures under permafrost or the deep sea, combined with favorable geological conditions for gas generation and storage, cover vast areas and indicate an immense potential for natural hydrocarbon gas in the upper 2 km of many Canadian sedimentary basins. We have analyzed the potential of gas hydrates for the vast continental shelves and Arctic permafrost regions of Canada (Mackenzie delta-Beaufort Sea and Arctic Archipelago in the north and Davis Strait, the Labrador Shelf, Scotian Shelf, and Grand Banks of Newfoundland along the Canadian Atlantic margin and Canadian Pacific margin). Our conservative calculation suggests 1010-1012 m3 of gas hydrates in these regions has an associated methane gas potential estimated to be in the range of 1012-1014 m3. The volume of methane in hydrates in Canada are geographically distributed in the following regions: 0.24-8.7 x 1013 m3 in the Mackenzie delta-Beaufort Sea, 0.19-6.2 x 1014 m3 in the Arctic Archipelago, 1.9-7.8 x 1013 m3 on the Atlantic margin, and 0.32-2.4 x 1013 m3 on the Pacific margin. The total in-situ amount of methane in hydrates of Canada is estimated to be 0.44-8.1 x 1014 m3, as compared to a conventional Canadian in-situ hydrocarbon gas potential of approximately 0.27 x 1014 m3. This comparison suggests that gas hydrates represent a possible future assurance of North American energy supply if the gas can be recovered and separated from the hydrate form.

A reappraisal of low-temperature thermochronology of the eastern Fennoscandia Shield and radiation-enhanced apatite fission-track annealing

Abstract We assess the proposal of Hendriks & Redfield (Earth and Planetary Science Letters, 236, 443–458, 2005) that cross-over of the predicted apatite fission track (AFT)>(U–Th–Sm)/He (AHe) age relationship in the southeastern Fennoscandian shield in southern Finland reflects α-radiation-enhanced annealing (REA) of fission tracks at low temperatures and that more robust estimates of the denudation history are recorded through reproducible AHe data. New AHe results from southern Finland showing variable dispersion of single-grain ages may be biased by different factors operating within grains, which tend to give a greater weighting towards older age outliers. AHe ages from mafic rocks show the least dispersion and tend to be consistently lower than their coexisting AFT ages. In general, it is at the younger end of the single-grain variation range from such lithologies where most meaningful AHe ages can be found. AHe data from multigrain aliquots are, therefore, of limited value for evaluating thermal histories in southern Finland, especially when compared against coexisting AFT data as supporting evidence for REA. New, large datasets from the southern Canadian and Western Australian shields show the relationship between AFT age, single-grain age or mean track length as a function of U content (determined by the external detector method). These do not display the moderately strong inverse correlations previously reported from southern Finland in support of REA. Rather, the trends are inconsistent and generally exhibit weak positive or negative correlations. This is also the case for plots from both shields, as well as those from southern Finland, where AFT parameters are plotted against effective U concentration [eU] [based on U and Th content determined by inductively coupled plasma-mass spectroscopy (ICP-MS)], which weights decay of the parents more accurately in terms of their α‐productivity. Further, samples from southern Finland yield values of chi-square χ2 >5%, indicating that there is no significant effect of the range of uranium content between grains within samples on the AFT ages, and that they are all consistent with a single population. The oldest AFT ages in southern Finland apatites (amongst the oldest recorded from anywhere) are found in gabbros, which also have the highest Cl content of all samples studied. We suggest, that it is Cl content rather than REA that has influenced the annealing history of the apatites, which have experienced a history including reburial into the partial annealing zone by Caledonian Foreland basin sedimentation. The study of apatite from low U and Th rocks, with relatively low levels of α-radiation damage may provide the most practical approach for producing reliable results for AFT and AHe thermochronometry studies in cratonic environments.

Hydrocarbon Favourability Mapping Using Fuzzy Integration: Western Sverdrup Basin, Canada

ABSTRACT There are several difficulties in characterizing geological conditions favourable for hydrocarbon accumulation in a frontier region due to the availability and nature of geoscience data. First, geoscience information from various sources requires precise representation for spatial analysis. In many cases, the information to be represented is possibilistic or transient in nature, and it needs a mathematical tool that can adequately represent the information with a degree of possibility and/or uncertainty. Second, the uncertainty of interpreting each geological indicator and of correlating the results with physical parameters of a petroleum accumulation should be expressed explicitly. Third, the evidence and indicators of the existence of a petroleum accumulation come from various data sources, varying in degrees of uncertainty. These uncertainties should be integrated into a petroleum accumulation model so that exploration risk can be objectively evaluated in a subsequent economic analysis. We propose the use of a fuzzy integration method to tackle these problems. The method uses possibility theory to describe the satisfaction levels associated with each of the essentials for the formation of hydrocarbon deposits, such as the presence of reservoir, source rock, trap, top seal and preservation in a spatial domain. The uncertainties associated with data and evaluation are explicitly incorporated in the aggregate of the geological factors. The proposed method was applied to the Heiberg Group/Formation of western Sverdrup Basin in the Canadian Arctic Archipelago to evaluate the geological favourability for petroleum accumulation. The discovered oil and gas fields and the areas with computed high favourability display a good geographical correspondence, indicating that the proposed fuzzy integration method captures the essential spatial characteristics of petroleum accumulations in the western Sverdrup Basin. End_Page 492------------------------

Geological risk mapping and prospect evaluation using multivariate and Bayesian statistical methods, western Sverdrup Basin of Canada

The current practice of geological risk evaluation at the play level involves substantial subjectivity and rarely considers the spatial correlations among the identified prospects. A quantitative procedure using multivariate and Bayesian statistical methods is proposed, which treats exploration-risk evaluation as a two-group classification, to provide a more objective and reproducible result. The spatial correlation among the identified prospects is considered because the proposed approach is applied to the entire evaluation area. The exploration-risk evaluation of the Upper Triassic–Lower Jurassic Heiberg Group structural gas play in western Sverdrup Basin, Arctic Canada, illustrates the method.

A Pool-Based Model of the Spatial Distribution of Undiscovered Petroleum Resoufrces

An approach is proposed to predict the spatial distributions of undiscovered petroleum resources. Each pool is parameterized as a marked-point. The independence chain of the Hastings algorithm is used to generate an appropriate structure for pool combinations in a play. Petroleum-bearing favorability estimated from geological observations is used to represent the sampling probabilities of pool locations. An objective function measuring the distance between characteristics of the realization and constraints is constructed from both the pool size distribution and entropy maximum criterion, in which the entropy criterion places all undiscovered pools in the most favorable positions. The geometrical convergence property of the proposed Hastings algorithm is presented. The method is illustrated by a case study from the Western Canada Sedimentary Basin.

Delineating compositional variabilities among crude oils from Central Montana, USA, using light hydrocarbon and biomarker characteristics

Abstract Three compositionally distinctive groups of oils identified in central Montana by biomarker analyses are also recognized by the unique compositions of their light hydrocarbon (gasoline range) fraction. The majority of oils produced from Paleozoic pools (Pennsylvanian Tyler–Amsden interval) group into one broad category based on the distribution of C 20 –C 40 biomarkers. These oils not only have the lowest Paraffin Indices and relative concentrations of normal heptane, but are readily distinguishable from the other compositional groups by using selected “Mango” parameters. However, the biomarker-based subdivision of this group into at least two sub-families is not reflected in the gasoline range fraction, suggesting little effect of source rock host lithology on the distribution of C 5 –C 8 hydrocarbons. Oils occurring predominantly in Jurassic–Cretaceous reservoirs display different biomarker and gasoline range characteristics, including Paraffin Indices, K1 parameter and relative concentrations of C 7 compounds, and are classified in two separate compositional categories. In contrast to oils from the Tyler–Amsden interval, the oils produced from the Mesozoic strata are amongst the most mature oils in the study area. The unique biomarker/light hydrocarbon signatures are likely due to different source organic matter. Secondary alteration of oil due to biodegradation and migration, although recognized, appears less significant. The results indicate the overall usefulness of gasoline range compositions in delineating compositional affinities of crude oils in central Montana, clearly suggesting that the oils found in Paleozoic and Mesozoic reservoirs belong to different petroleum systems.