Browsing by Author "Bentley, Laurence"

Now showing 1 - 13 of 13
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    A Geophysical Investigation of a Rock Glacier in the Canadian Rockies
    (2016-01-18) Mozil, Alexandra; Bentley, Laurence; Bentley, Laurence; Hayashi, Masaki; Moorman, Brian
    In this project a geophysical survey was conducted on the rock glacier in the Helen Lake watershed (Ban National Park, Alberta, Canada) to investigate its internal structure. Geophysical methods involved electrical resistivity tomography, seismic refraction and ground penetrating radar. The main objectives were (1) to identify the presence of ice, (2) determine the depth to bedrock and (3) trace the pathways of ground water flow. The conceptual model of the rock glacier was built based on the interpretation of geophysical data sets. It showed that the rock glacier represents an important hydrological unit playing a significant role in storage and release of water sustaining the late summer flow in the watershed. This research contributes to the understanding of how such hydrological units as rock glaciers function and what predictions could be made about the consequences of the climate warming for these natural water reservoirs.
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    Advancing Electrical Resistivity Tomography as an Environmental Monitoring Tool in Seasonally Frozen Ground: Linking Lab and Field Scales
    (2021-03-15) Herring, Teddi; Cey, Edwin; Pidlisecky, Adam; Bentley, Laurence; Lauer, Rachel; Karchewski, Brandon; Ferré, Ty
    When time-lapse electrical resistivity tomography (ERT) is used as an environmental monitoring tool, the effects of temperature variability should be taken into account to avoid erroneous interpretations of subsurface processes. In regions where the near-surface freezes seasonally, removing the effects of temperature is a non-trivial task. One limiting factor is the poorly understood relationship between electrical resistivity and temperature under frozen conditions. A laboratory experiment was conducted that quantified this relationship and related resistivity to unfrozen water content and fluid resistivity using a modified version of Archie’s equation. A second limiting factor is that the standard inversion has a limited ability to resolve sharp boundaries and large contrasts in resistivity, like those seen between frozen and unfrozen regions. A synthetic time-lapse ERT modelling study showed that because standard ERT inversion techniques were unable to accurately recover the resistivity of the frozen surface layer, temperature corrections applied to these models performed poorly. In this synthetic experiment, modifications to data acquisition (burying electrodes or reducing electrode spacing) and regularization strategy (increasing lateral smoothness, reducing regularization across boundaries, or using an L1 model misfit norm) did not appreciably improve the outcomes of temperature corrections in partially frozen ground. A hybrid inversion strategy was developed to incorporate prior information about the geometry of the frozen layer in the inversion. The hybrid inversion used a parametric approach with only depth and a single resistivity to describe the frozen layer, while the rest of the model space was described with a large number of voxels. A synthetic experiment showed that the hybrid inversion improved resolution of a frozen surface layer and features beneath it compared to a standard smooth inversion. The improved resistivity models resulted in lower errors in the temperature-corrected data. However, resolution of the frozen layer was still limited by the information content of the data, regardless of inversion strategy. Altogether, this study improves our understanding of the physical processes and relationships that govern resistivity at subzero temperatures, highlights limitations of standard data processing strategies, and demonstrates the efficacy of a hybrid inversion approach for ERT data collected in partially frozen ground.
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    Delineating the Shallow Free-phase Gas Distribution at an Abandoned Exploration Well, Crystal Geyser
    (2022-01-20) Lagasca, Patrick Arceo; Ryan, M. Cathryn; Bentley, Laurence; Eaton, David
    Crystal Geyser is an abandoned exploration well and active cold-water geyser driven by the expulsion of CO2 gas. It is a case study of an unsealed well transporting stray CO2 gas to the surface. Previous studies in the Crystal Geyser area inferred the existence of free-phase gas (FPG) accumulations trapped beneath low permeability layers near the geyser, but did not specify their exact locations or depths. In our primary study, we used electrical resistivity tomography to image a siltstone-capped FPG plume within the sandstone aquifer beneath Crystal Geyser. The plume was identified from an anomalously high resistivity zone that was not caused by lithofacies changes or fault displacement, representing a portion of the aquifer with elevated FPG content in the pore space. FPG is transported via Crystal Geyser’s conduit and the nearby Little Grand Wash Fault into a plunging anticline trap. The poor well casing integrity allows FPG to migrate from the conduit into the surrounding aquifer and gas trap. The subsurface FPG plume delineation was compared to the “equivalent CO2 bubbling depth” – the shallowest depth at which the total CO2 mass (free-phase and dissolved-phase CO2) expelled from the geyser would occur in the dissolved phase. The bubbling depth was extrapolated from mass balance calculations based on field estimates of Crystal Geyser’s CO2 and water emissions. The estimated bubbling depth was much shallower than the imaged FPG plume. This underestimation can be caused by the leakage of ascending FPG into the surrounding subsurface, allowed by the poor casing integrity of the well.
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    Estimating Specific Storage and Matrix Compressibility from Barometric Efficiency in the Southern Alberta Paskapoo Aquifer System
    (2015-12-15) Augustine, Natasha; Bentley, Laurence; Cey, Edwin; Hildebrand, Alan
    Specific storage (Ss) and matrix compressibility (α) are fundamental aquifer properties which can be estimated by barometric efficiency (BE), a measure of well response to changes in barometric pressure. Five BE estimation techniques (amplitude ratio analysis, Clark method, Rahi method, graphical ellipse, and barometric response functions) are discussed and a standardized technique for estimating BE, pre- and post-analysis data conditioning (PPC) is described. It is shown that this technique can greatly improve the consistency of BE estimates and that small scale resolution errors rather than large scale noise may impact results the most. The PPC approach and an inter-quartile range filter are applied to data obtained from the Paskapoo formation and BE, Ss, and α estimates are derived (ranging from 3.9-99.5%, 8.3x10-7-1.7x10-5 m-1 and 1.6x10-11-1.7x10-9 Pa-1, respectively). It is demonstrated that the outlined techniques allow data from non-traditional sources (active pumping wells and legacy monitoring wells) to be employed.
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    Gamma ray normalization and Regional Fluvial Architecture: The Paleocene Paskapoo Formation, Alberta
    (2014-04-28) Quartero, Erik; Bentley, Laurence; Leier, Andrew
    The Paskapoo formation is composed of several hundred meters of heterogeneous fluvial strata that were deposited in the subsiding foreland basin of the Canadian Cordillera. The Alberta government require the gamma ray log from petroleum wells to be collected through this formation. The first step in utilizing this new data is to correct for the suppressive effect that surface casing has on the natural gamma ray response. A simple and efficient method was used to normalize the gamma ray data collected through surface casing. The method adjusts the cased gamma ray values so that the maximum and minimum of the distribution are equal to those of non-cased values. Net-to-gross maps and stratigraphic cross-sections identify a megafan/DFS in the north and variation in the fluvial stratigraphy across the study area. Tectonic activity is interpreted as the primary control on fluvial stratigraphy, controlling the variable ratio of sediment flux to accommodation creation.
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    Geophysical Characterization of an Undrained Oil Sands Tailings Pond Dyke Alberta, Canada
    (2014-09-23) Booterbaugh, Aaron; Bentley, Laurence
    Geophysical characterization of an undrained oil sands tailings pond dyke was conducted at Syncrude Canada’s Southwest Sand Storage Facility (SWSS). Push tool conductivity (PTC), electromagnetic (EM), and electrical resistivity tomography (ERT) methods in conjunction with hydrogeological and chemistry measurements were used to investigate soil moisture, hydraulic head, and groundwater salinity distributions. Normalization and calibration procedures were conducted on EM data to build statistically consistent maps between survey years. An Archie’s Law petrophysical model was utilized to relate measured bulk conductivity, from geophysical surveying, with measures of soil moisture and fluid electrical conductivity. It was found that a relatively strong relationship between bulk electrical conductivity and soil moisture exists, while weak to no correlation was observed between bulk and fluid electrical conductivity. ERT surveying was capable of clearly identifying the location of the water table within the dyke. This study provides a unique look into the application of geophysical techniques to investigate soil moisture, hydraulic head, and salt distribution in an active undrained tailings dam structure.
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    Geophysical Characterizations of the Paskapoo Formation
    (2013-09-24) Zhi, Lei; Bentley, Laurence
    The petrophysical statistics of Paskapoo Formation lithologies were established from five Alberta Geological Survey boreholes after the lithologies were reclassified into a smaller set of groups. The study focused on gamma, density, resistivity, and sonic logs. Results show that 92 API and 19 ohm.m is the gamma and resistivity cutoff between sandstone and mudrock, and indicate that electrical resistivity method can be used to distinguish lithology of the Paskapoo Fm., while seismic refraction method has limited usage. Electrical resistivity and seismic refraction data were collected in a field site, Priddis, Alberta and processed to test the feasibility of the two methods to constrain the subsurface architecture. With the assistance from Priddis borehole and the combined interpretation of the two tomograms, results show the depth to the bedrock ranges from 5 to 10 m and heterogeneous upper part of the bedrock is dominated by sandstone and mudrock.
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    Geophysical Monitoring Of Salt Remediation
    (2013-06-26) Head, Franklin; Bentley, Laurence
    A site near Devon, Alberta was used to monitor salt transport over time and test the effect of irrigation. Direct push EC (PTC) was regressed against coincident chloride concentration measurements from soil cores. The PTC EC data was then converted to chloride measurements. Using the EM-31 instrument, two site-wide surveys were taken in 2008 and 2010 and both were regressed against coincident PTC EC data converted to chloride. The EM-31 survey was converted to chloride using the regression relationship. Salt mass was determined by kriging with a locally varying mean (KLVM) and found an increase of 3 tonnes which is within our uncertainty. A 20 by 20 m test plot was surveyed using ERT in 2009 and 2010. ERT results were regressed against chloride samples. ERT was transformed by the regression relationship. KLVM was used with chloride samples and transformed ERT and found a decrease of 32% in chloride mass.
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    Pine Creek Geophysical Data
    (2007-08-16T20:56:10Z) Bentley, Laurence; Hirsch, Markus
    You are free to download and use the data on this website for educational or research purposes. If the data or processing results are used in publications or educational materials, you should acknowledge their source by citing: Hirsch, M., Bentley, L.R., and Dietrich, P., “A comparison of electrical resistivity, ground-penetrating radar and seismic refraction results at a river terrace site, JEEG, (in press). You must have written permission from the authors to use any portion of the data or results derived from the data for any commercial purposes. This web site contains raw data, surveying coordinate and borehole logs from a multi-method geophysical survey collected on Bow River terrace at the Pine Creek field site in city of Calgary, southern Alberta. Some of the data have been presented in paper entitled “A comparison of electrical resistivity, ground-penetrating radar and seismic refraction results at a river terrace site” by Hirsch, M., Bentley, L.R., and Dietrich, P. (Journal of Environmental and Engineering Geophysics, in press). The entire survey is described in “Geophysical survey on Pine Creek field site Calgary, Alberta Canada, Hirsch, M., M.Sc. Thesis, University Tübingen (2004) which is available on this web site. The geophysical survey includes collocated electrical resistivity imaging (ERI), ground penetrating radar (GPR), and seismic refraction along three relatively long profiles. Line locations in local and UTM coordinate systems as well as topographical data along the three profiles are also provided. The ERI data set includes ascii apparent resistivity values for Wenner configuration with different unit electrode spacings (2 m, 3 m, and 4 m). The GPR data set includes constant offset (1 m) time series using 100 MHz antennas as well as the CMPs experiments at several locations along the three profiles. The seismic refraction data set contains raw time series in SEG2 format as well as first-arrival travel-time picks along the three lines. Complementary information such as borehole logs along the survey lines is also included. We envision that this high quality data set will be useful for educational purposes, such as processing and interpretation laboratories. It will also be useful as a test data set for processing computer code development in areas such as joint inversion of multiple types of geophysical data. File “Summary” summarizes description of the data files, locations, formats and tools.
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    Pore Morphological Multi-Phase Digital Rock Physics Models
    (2016) Mohammadmoradi, Seyed Peyman; Kantzas, Apostolos; Sahimi, Muhammad; Clarkson, Christopher; Maini, Brij; Dong, Mingzhe; Bentley, Laurence
    To reduce expenses, failures, ecological footprints, and uncertainty of reservoir appraisal operations, digital rock physics workflows need to be evolved constantly. The traditional characterization procedures are being replaced by technology-rich environmentally sustainable virtual packages. The advancing high-resolution imaging technology offers the opportunity to directly capture exhaustive pore-level images and highlights the need for fast, reliable and multi-phase simulation techniques. Performing direct multi-phase simulations and tracking fluid-fluid and fluid-solid interfaces are the most essential and challenging parts of pore-level studies. There is a technical dilemma in the direct simulation of immiscible displacements between dynamic, e.g. CFD and Lattice-Boltzmann, and quasi-static, e.g. pore morphological, approaches. Once the partially saturated micro-scale realizations are generated, the effective mechanical, petrophysical and thermo-physical properties can be predicted applying steady-state simulations through solid fabrics and fluids spatial arrangements. In this thesis, direct voxel-based pore-level fluid flow models are proposed, validated and applied to real and synthetic porous media images. Two- and three-phase quasi-static pore morphological algorithms are first presented to simulate immiscible displacement processes and post-processing results are compared with experimental data available in the literature. The workflows are applied to predict thermo-physical and petrophysical characteristics of porous media from the pore-scale point of view. The filling process is adapted applying an object-based technique and the marching cubes algorithm is utilized to extract spreading and wetting films. To deal with the multi-scale nature of porous media and extent the capability and universality of the approach, a hybrid approach called DyMAS (Dynamic Morphology Assisted Simulation) is then proposed coupling pore morphological and CFD-based dynamic workflows.
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    Seismic attenuation measurements from multicomponent vertical seismic profile data
    (2017) Montano Spagnolo, Michelle; Lawton, Donald; Margrave, Gary; Bentley, Laurence; Trad, Daniel
    Vertical seismic pro le (VSP) data provide a means to estimate the seismic wavelet at different receiver depths. The downgoing wavefi eld has always been the key to measure attenuation (Q) and enables us to correct for the effects of seismic attenuation on seismic data. We demonstrate that we can also use the upgoing wave field to estimate Q, using reflections and mode-converted waves. In this work, Q is estimated from synthetic VSP downgoing and upgoing wavefi elds by using the spectral matching method. We also estimated Q, using the spectral matching method, from VSP data collected in a 500 m deep well in a heavy oil field and a 2000 m deep well in a shale gas play in Western Canada. For the first case, we obtained values of Qp of approximately 50 and Qs of 20 for the strata intersected by the well. For the second case, we obtained values of Qp of approximately 50 and Qs of 30. In the case of Qs estimations, our results indicate that using the upgoing converted wave field provides good estimations when downgoing S-wave are not available in the data.
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    The Hydrogeology of a Rock Glacier and Its Effect on Stream Temperature
    (2017) Harrington, Jordan Shane; Hayashi, Masaki; Bentley, Laurence; Marshall, Shawn
    Rock glaciers can be important aquifers that supply streamflow during dry periods and provide cold-water refuges in mountain streams. This study investigated the hydrogeological and thermal processes within an inactive talus rock glacier, and the effects of its groundwater discharge on stream temperature. Permafrost in the rock glacier is associated with the presence of large coarse blocky surficial materials, and appears to have minimal effect on groundwater flowpaths and sources. The primary control on groundwater flow and storage in the rock glacier is the hydrostratigraphy at the rock glacier base, where water inputs displace long-term groundwater storage. Either a basal low-conductivity layer (‘transmissivity feedback’ mechanism) or depressions in fractured bedrock (‘fill-spill-drain’ mechanism) are postulated to represent this control. The cold groundwater discharged from the rock glacier strongly cools the adjacent creek, providing a cold-water refuge that may be resilient to climatic warming.