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- ItemOpen AccessSequence stratigraphic framework for top seal development: examples from the Skull Creek and Graneros shales, Denver basin(Colorado State University. Libraries, 1999) Edwards, Kimberly, K., author; Sutton, Sally J., advisor; Ethridge, Frank G., advisor; Almon, William R., committee memberIn general, the distal open marine shelf setting, typified by the Graneros Shale produces a rock with a greater and more uniform seal capacity relative to the rocks of a proximal open marine shelf setting, such as those of the Skull Creek Shale. A distal setting, which usually corresponds to the time of maximum transgression, may produce better seals because there is less coarse clastic sediment input, which allows slow deposition of clays from suspension to be the dominant depositional process. In this study, the higher capacity seal rocks occur in the upper parts of the TST, either within the condensed section or below it. The Skull Creek locations show seal occurrence to be stratigraphically higher on depositional topographic highs, and lower in areas that were topographically low at the time of deposition. Top seal capacity was quantified with mercury injection capillary pressure (MICP) analysis. Other physical characteristics of these marine shales were studied but only porosity, permeability, total clay, and hydrogen index consistently demonstrated a significant correlation with seal capacity in both units. Shales that are well laminated with a high percentage of total clay and/or total organic carbon with a type I-II (marine) kerogen may or may not qualify as the best seal. Top seal capacity may be more a function of rock fabric rather than mineralogy. For example, two samples may have exactly the same amount of quartz, as shown by XRD analysis, but thin section examination reveals that the majority of quartz in one sample is present as grains and in the other sample as cement. Samples with cement usually provide a better seal because they decrease the pore throat diameter, thus increasing the amount of hydrocarbons that can be trapped. Seal quality in both the Skull Creek and Graneros Shales is quite variable throughout each of the facies within the TST deposits.
- ItemOpen AccessForm and function: quantifying geomorphic heterogeneity and drivers in dryland non-perennial river corridors(Colorado State University. Libraries, 2023) Scamardo, Julianne E., author; Wohl, Ellen, advisor; McGrath, Dan, committee member; Morrison, Ryan, committee member; Rathburn, Sara, committee memberNon-perennial rivers, including intermittent rivers and ephemeral streams, comprise the majority of drainage networks globally. However, ephemeral streams remain understudied compared to perennial counterparts, and the majority of extant studies focus on in-channel dynamics. Floodplains along perennial streams are known to host a high density of ecosystem functions, including the attenuation of downstream fluxes and provision of habitat to diverse flora and fauna. These functions are thought to be correlated to geomorphic heterogeneity, and studies of floodplain heterogeneity are emerging on perennial rivers. Here, I extend the conceptualization of floodplain function and heterogeneity commonly focused in perennial watersheds to dryland, ephemeral streams. Based on a synthesis of current literature identifying ephemeral stream floodplain characteristics in drylands, a set of floodplain styles emerge dependent on confinement and the presence of channelized flow. Functions related to attenuation and storage are typically concentrated in unconfined and channeled floodplains. The temporary storage of sediment and sub-surface water in ephemeral stream floodplains make them hotspots for biogeochemical cycling and hosts to richer, denser, and more diverse vegetation communities compared to surrounding uplands. Many functions of ephemeral stream floodplains are also found in perennial counterparts, but flashy flow regimes and high sediment loads in ephemeral streams can potentially impact rates and magnitudes of comparable processes and functions. Similar to perennial rivers, the diverse physical and ecological functions in ephemeral stream floodplains are thought to be related to spatial geomorphic heterogeneity. Although studies on the characteristics and drivers of geomorphic heterogeneity exist for perennial streams, similar studies in ephemeral streams are lacking. Geomorphic heterogeneity was therefore quantified along with potential drivers – including metrics related to geomorphic context and proxies for flood disturbance – to understand underlying processes in ephemeral river corridors. Geomorphic units were mapped in 30 unconfined river corridors within six non-perennial watersheds in Utah and Arizona, U.S. Landscape heterogeneity metrics – Shannon's Diversity Index, Shannon's Evenness Index, and patch density – were used to quantify geomorphic heterogeneity within each reach. Additionally, variables that potentially constrain or drive heterogeneity were quantified, including floodplain shape, grain size, large wood abundance, channel change and sediment storage times. Although heterogeneity positively correlated with metrics for morphology and disturbance (i.e., channel change and storage), statistical models suggest that morphologic context, particularly floodplain width, was a more important predictor for estimating geomorphic heterogeneity. Still, geomorphic units reflected aggradation processes indicative of a range of flood energies, suggesting a strong tie between heterogeneity and disturbance. Results suggest that non-perennial rivers with greater geomorphic heterogeneity may be resilient to changes in flood disturbance frequency or magnitude, but future studies investigating long-term temporal heterogeneity are needed. The lack of direct flux observations could also be restricting insight into how floods interact with large wood and vegetation, which are known to have complex relationships with geomorphic heterogeneity in perennial rivers. In the absence of flood observations, a hydro-morphodynamic model was developed to investigate changes to channel and floodplain morphology due to wood and vegetation in an ephemeral river corridor in southeastern Arizona, U.S. Three scenarios were modeled: the actual configuration of the river corridor; an experiment in which jams were removed; and an experiment in which vegetation was removed. Both large wood and vegetation effectively confined flow to the main, unvegetated channel, which became wider and deeper over the course of a single moderate flood. When isolating the impact of large wood, model results show that wood increases the magnitude of channel change created by vegetation, resulting in ±0.1 to 0.3 m of additional scour or aggradation. The simulated removal of vegetation resulted in more channel change than the removal of wood alone, partially because vegetation occupies a much greater area within the stream corridor than large wood. I propose a conceptual framework in which large wood could mediate sedimentation as well as the recruitment and growth of vegetation in ephemeral streams, contributing to the evolution of ephemeral stream morphology over time. Due to the ubiquity of dryland ephemeral streams, results of this research have the potential to influence watershed management globally. Wide, unconfined ephemeral stream floodplains and riparian forests could be targets for protection and restoration similar to current efforts in perennial rivers. Particularly in the context of future climate and land use changes, understanding the natural character, function, and heterogeneity of ephemeral stream floodplains highlights their physical and ecological importance in dryland landscapes.
- ItemOpen AccessDammed ponds! A study of post-fire sediment and carbon dynamics in beaver ponds and their contributions to watershed resilience(Colorado State University. Libraries, 2023) Dunn, Sarah B., author; Rathburn, Sara, advisor; Wohl, Ellen, committee member; Morrison, Ryan, committee memberExcess sediment generated by wildfires threatens stream water quality, riparian habitat, and infrastructure. Beavers construct dams that pool water and capture sediment. Beaver ponds may bolster watershed resilience by providing sediment and carbon storage following wildfire. I tested the hypotheses that (1) burned ponds store greater relative volumes of sediment compared to unburned ponds, (2) post-fire sedimentation rates exceed pre-fire and unburned rates, and (3) post-fire sediment stored in beaver ponds is coarser and has a higher abundance of organic carbon relative to pre-fire sediment. I surveyed 48 beaver ponds in the Colorado Rocky Mountains. Approximately half of the ponds are in areas that burned in 2020 wildfires, whereas the other half remain unburned. Sites also spanned a range of geomorphic, vegetation, and individual pond characteristics. I conducted sediment probe surveys and collected sediment cores to quantify pond sediment storage and characterize sediment composition. Stratigraphic units present in sediment cores were analyzed for grain size and total organic carbon (TOC). Results indicate that beaver ponds in the Rocky Mountains store high volumes of sediment (mean = 796 m3). Burned ponds contain statistically significantly more relative sediment storage and have higher sedimentation rates than unburned ponds. Beaver ponds recorded high post-fire sedimentation rates (median = 19.8 cm/yr). Moreover, post-fire sedimentation rates are an order of magnitude higher than pre-fire rates in ponds with both pre- and post-fire sediments. Total sediment volume, sedimentation rates, grain size, and TOC content did not vary significantly between burned and unburned ponds. Geomorphology, vegetation, and pond characteristics exert additional influences on pond sediment dynamics. Pond characteristics determine the sediment trapping efficiency of ponds. Larger ponds store greater volumes of sediment, as do off-channel and older ponds. Ponds abandoned by beaver store greater volumes of sediment than actively maintained or human- constructed dams. Beaver activity and dam maintenance is critical for maintaining storage availability in ponds. Additionally, sedimentation rates are higher in ponds that are on-channel and recently constructed compared to off-channel and older ponds. These findings indicate that beaver-based restoration can be implemented prior to fire to provide critical post-fire sediment storage, thus enhancing watershed resilience and recovery.
- ItemOpen AccessGeochemical modeling-based prediction of water-rock interaction during aquifer storage and recovery utilizing selected Colorado Front Range aquifers(Colorado State University. Libraries, 2023) Doherty, Amanda, author; Sutton, Sally, advisor; Sale, Thomas, committee member; Ronayne, Michael, committee memberThis study characterizes the Fountain Formation, Ingleside Formation, and sandstones of the Dakota Group and considers the potential of these three formations as hypothetical Aquifer Storage and Recovery (ASR) targets. Compositional data from surface rock samples, including major, minor and trace elements from bulk rock geochemical analysis and mineral identification from petrography are used to infer a generalized mineral suite to represent each of the formations of interest. Similarly, compositional analyses from domestic water well samples, including major anions and cations and selected metals, were used as generalized representations of native water from each formation of interest. Finally, compositional data from treated city water was obtained and used as a generalized representation of injection water. The generalized rock data along with the generalized native water data represent a hypothetical injection environment while the treated water composition represents a hypothetical injection water. All water and rock data were used to populate a Single Pass Mixing equilibria Model that simulated an ASR system using the USGS geochemical modeling computer program PHREEQC (PH REdox EQuilibrium). Model results include mixed solution compositions, mineral saturation indices and estimates of mineral mass precipitation during simulated injection. Results of modeling suggest there is limited geochemical water-rock interaction during ASR in the hypothetical environment in this study. Model results indicate that the mixed solution composition is controlled more by the injected solution than by reactions occurring between the injection fluid and aquifer host material. Specifically, as greater volumes of hypothetical injection water are introduced with each model step, the compositions of the resulting mixed solutions increasingly resemble those of the injected water. The model predicted the precipitation of hematite, kaolinite and quartz during injection of the hypothetical injection water. Because aluminum was below detection in the water analyses and an arbitrary value less than the detection limit was used in the model, the prediction of kaolinite precipitation is not meaningful. Further, the model was constrained to not permit mineral dissolution, limiting the applicability of the model only to the consideration of mineral precipitation. In addition, benchtop leaching experiments were performed on rock samples to provide additional information about potential water-rock interaction. Benchtop experiment results are presented, but the focus of the study is primarily on geochemical modeling results. Water analysis results presented here suggest that the formations of interest currently contain good quality water. Modeling results suggest that injection of treated water would likely not lead to volumetrically important precipitation of minerals in the formations.
- ItemOpen AccessModeling of channel stacking patterns controlled by near wellbore modeling(Colorado State University. Libraries, 2023) Escobar Arenas, Luis Carlos, author; Stright, Lisa, advisor; Ronayne, Michael, committee member; Barnes, Elizabeth, committee memberReservoir models of deep-water channels rely upon low-resolution but spatially extensive seismic data, high vertical resolution but spatially sparse well log data and geomodeling methods. The results cannot predict architecture below seismic resolution or between well logs. Usually, the data and interpretations that provide constraints for modeling workflows do not capture sub-seismic scale architecture. Therefore, standard modeling methods do not generate models that include details that can impact hydrocarbon flow and recovery. Constraining models to well and seismic data is problematic. Employing measured sections in the Tres Pasos Fm. (Magallanes Basin, Chile) is feasible to predict deep-water channel architecture, specifically channel stacking patterns with 1D information analogous to well data. This research performed near-wellbore modeling to generate multiple scenarios of channel stacking patterns constrained by machine learning-derived probabilities using (i) conditional Monte Carlo simulation with soft probabilities per channel element within the measured section choosing the highest probabilities for each element (ii) conditional Monte Carlo simulation of channel stacking, (iii) template-based modeling, (iv) forward modeling with Markov transition probabilities without matching to thickness and (v) conditional Monte Carlo simulation constrained to measured section thickness. Machine learning workflows generate channel position probabilities (i.e., axis, off-axis, margin) within a measured section given the interpreted top/bases of channel elements. These probabilities constitute the input for Monte Carlo simulations capturing channel element stacking patterns at the measured section locations. The most likely 2D channel stacking pattern scenarios defined channel centerline points, and volumes of the individual channel elements can be generated connecting them. Surface-based modeling offers a way to depict reservoirs of hydrocarbons, water or low-enthalpy geothermal systems in which small-scale heterogeneity needs to be captured explicitly by bounding surfaces because it impacts fluid flow, improving our forecasts of resource exploitation. Furthermore, predicting heterogeneity controlled by depositional architecture is critical for transport and storage capacity in CO2 reservoirs. The dataset provided and the advent of these flexible and accurate methods to depict the subsurface offer the opportunity to overcome the historical limitations of grid-based models and allow us to assess multi-scale architecture that controls fluid flow. This research aims to show the results of modeling deep-water channels, including a 1D identification of architectural positions and a 2D arrangement of channel stacking patterns.