• Landslides in the Fairbanks North Star Borough, Alaska: inventory map and Tanana 440 landslide assessment

      Schwarber, Jaimy A.; Darrow, Margaret; Kidanu, Shishay; Daanen, Ronald (2021-12)
      Landslides are geologic hazards that threaten human life, property, and infrastructure. Effective threat mitigation requires knowledge of where past landslides occurred. Until now, no published landslide inventory maps existed for any part of Alaska. Here we present an overview of our landslide mapping within parts of the Fairbanks North Star Borough (FNSB), Alaska and a thorough investigation and assessment of the Tanana 440 (T440) landslide. We mapped 1,679 landslides, and field-verified 51 landslides within the FNSB. These landslides vary in age, movement type, and material. Most are prehistoric, but we did observe some historic and active landslides. Observed slope failures include flows in soil, translational and rotational slides in bedrock, and complex features that combine multiple types of movement. Potential landslide triggers may include thawing permafrost, increased pore water pressure conditions, seismic events, and river erosion. The landslide inventory map, the first of its kind for Alaska, directly benefits the Borough, the State, and the general public, as it can be used by public agencies to make informed land management decisions and to incorporate landslides within multiple-disaster scenarios. Additionally, the map serves as the foundation for future landslide analysis within the FNSB. We also present results of in-depth mapping, subsurface exploration, soil engineering properties, and slope stability analysis of the T440 landslide. Based on analysis of stratigraphy, soil testing, and geomorphology, we determined the T440 landslide is a flow slide in loess that occurred during the late Pleistocene to mid-Holocene. Our modeling results suggest that thawing permafrost and/or seismic loading were possible triggers for the T440 landslide. We also present the first comprehensive direct shear testing of non-plastic silt with variation in moisture content, as well as the first comparison of direct shear and field vane shear measurements of silt. These results can be used for engineering design purposes for Interior Alaska silt for any gravimetric water content over 5%.
    • Study on emulsification/demulsification behavior and mechanism of produced liquid from polymer flooding on Alaska North Slope

      Chang, Hongli; Zhang, Yin; Dandekar, Abhijit; Trainor, Tom; Guerard, Jennifer (2022-05)
      Heavy oil reservoirs on Alaska North Slope (ANS) are unconsolidated and contain abundant clay minerals, where the first-ever field pilot is currently implemented to validate the use of polymer floods for heavy oil enhanced oil recovery (EOR). The polymer molecules and/or fine clay particles carried with the produced liquid could potentially affect the oil/water separation, which is one of the major concerns for field operators. This dissertation aims to investigate the emulsification behavior of produced liquid, understand the emulsifying mechanism, and seek an adaptive and cost-effective method to treat the produced liquid from polymer flooding. Emulsions were prepared by mechanically mixing the actual heavy oil and the produced water from the pilot site, of which the stability was investigated by bottle test method or multiple light scattering method. Drop size distribution and interfacial properties were measured via microscope and pendant drop technique to probe the stability mechanism further. Results showed that oil-continuous or water-continuous emulsion could be generated depending on the water cut, clay types, clay concentration, and polymer concentration. In the crude oil/water system, the increasing water cut triggered the phase inversion of oil-continuous emulsion to water-continuous emulsion, resulting in faster separation and lower emulsion stability. Whereas, clay particles, no matter added to the oil or water phase, resulted in an unfavorable phase inversion from the loose watercontinuous emulsion to the tight oil-continuous emulsion as clay concentration increased. For all four types of clay except Ca-montmorillonite, clay particles added to water led to an earlier phase inversion and higher emulsion stability than that added to the oil. The dual function of polymer on emulsion stability was observed. On the one hand, both sheared and unsheared polymer tended to convert the oil-continuous emulsion formed in either crude oil/water system or complex crude oil/water/clay particle system to the water-continuous emulsion, acting as a weak demulsifier to accelerate the oil/water separation. On the other hand, the addition of polymer to the watercontinuous emulsion could result in enhanced emulsion stability, which is primarily attributed to the increased viscosity of the continuous phase and the decreased drop size of the dispersed oil phase. Particularly, the sheared polymer had a weaker ability to stabilize the o/w emulsion than the unsheared polymer due to the lower viscosity of the sheared polymer solution resulting from the breakdown of the polymer macromolecules. As for the chemical demulsification tests, the performance of demulsifiers showed a complex dependency upon the water cut, the shearing intensity, demulsifier type and dosage, and the polymer concentration. A compound emulsion breaker, E12+E18, exhibited the most satisfactory demulsification performance despite the varied test conditions. For severe water-continuous emulsions that might require a multi-fold dosage of demulsifier, a less expensive electrolyte, KCl, was proposed to be used in combination with demulsifier E12+E18 to improve the demulsification performance. In the proposed demulsifier formula, the effectiveness of the commercial demulsifier relied on its destructive effect on the interfacial film, while the efficacy of KCl was mainly dependent on its viscosity reduction effect on the continuous phase. This dissertation illustrates that intermediate layer elimination and water clarification are the major challenges for produced liquid treatment from polymer flooding. It also provides practical and theoretical guidance in advance for the demulsification strategy of the produced liquid from the ongoing first-ever polymer flooding pilot on ANS.
    • Experimental investigation of nonthermal enhanced oil recovery techniques for improving oil recovery on Alaska North Slope

      Cheng, Yaoze; Zhang, Yin; Dandekar, Abhijit; Ahmadi, Mohabbat; Li, Xiaoli (2022-05)
      Exploitation of viscous and heavy oils on Alaska North Slope (ANS) requires nonthermal enhanced oil recovery (EOR) techniques. Currently, three nonthermal EOR methods, including solvent injection, low salinity water (LSW) flooding, and low salinity polymer (LSP) injection, have been proved to be useful on ANS. ANS viscous and heavy oils can be developed effectively by combining those three nonthermal EOR techniques. In this dissertation, lab experiments have been conducted to investigate the potential of the proposed hybrid nonthermal EOR techniques, including HSW (high salinity water)-LSW-softened LSW flooding, HSW-LSW-LSP flooding, CO₂-enriched LHS (light hydrocarbon solvent)-alternating-LSW flooding, LHS-alternating-LSW flooding, CO₂-enriched LHS (light hydrocarbon solvent)-alternating-LSP flooding, and LHS-alternating-LSP flooding, to improve ANS viscous oil recovery. Besides, the effect of essential clay minerals, including sodium-based montmorillonite (Na-Mt), calcium-based montmorillonite (Ca-Mt), illite, and kaolinite, on LSW flooding has been examined. In addition, the CO₂ influence on solvent-alternating-LSP flooding in enhancing ANS viscous oil recovery has been investigated. Furthermore, the blockage issue during CO₂-enriched LHS-alternating-LSP flooding has been investigated, and its solution has been proposed and analyzed. The EOR potential of the proposed hybrid EOR techniques has been evaluated by conducting coreflooding experiments. Additionally, relative permeability, swelling property, zeta potential, interfacial tension (IFT), and pressure-volume-temperature (PVT) tests have been conducted to reveal the EOR mechanisms of the proposed hybrid EOR techniques. Moreover, water ion analysis of DI-water/natural-sand and DI-water/natural-sand/CO₂ systems has been carried out to reveal the complex reaction between CO₂, sand, and LSP solution. It was found that, compared to conventional waterflooding, all the proposed hybrid EOR techniques could result in better oil recovery potential. It was noticed that the presence of CO₂ in LHS could be more beneficial to the solvent-alternating-LSW/LSP flooding processes during the 1st cycle due to the greater effectiveness of oil viscosity reduction. In particular, severe blockage issue occurred when conducting CO₂-enriched LHS-alternating-LSP flooding using sand pack due to the polymer precipitation. Additionally, the calculated water relative permeabilities are much lower than the typical values, implying more complex interactions between the reservoir rock, heavy oil, and injected water. Moreover, comparing to HSW, LSW could further swell Na-Mt significantly, which may benefit LSW flooding by improving sweep efficiency since in-situ swelling of Na-Mt has the potential to block the higher permeable water-flooded zone and divert the injected brine to lower permeable and unswept area. Comparing to Na-Mt, LSW couldn't swell Ca-Mt and illite further, whereas kaolinite was incapable of swelling in both HSW and LSW. Furthermore, about 60 mole% of solvent could be dissolved into the ANS viscous oil at target reservoir condition, resulting in oil swelling and viscosity reduction effects, which provided better microscopic displacement efficiency. Although the presence of CO₂ in LHS had a negative impact on the oil swelling effect, the influence on the oil viscosity reduction was positive. In addition, reducing the salinity of water could generate more negative zeta potential values on the surface of clay minerals and sand, making it more water wet. Besides, IFT of oil/LSW system is higher than that of oil/HSW system, indicating that IFT reduction is not an EOR mechanism of LSW flooding in our proposed hybrid EOR techniques. Additionally, after introducing CO₂ to the DIwater/natural-sand system, the concentration of multivalent cations was increased, which may be responsible for the polymer precipitation. The blockage issue could be solved by injecting LSW as a spacer between CO₂-enriched LHS injection and LSP injection.
    • Optimization and forecasting algorithms for converter dominated distribution networks using blockchain and AI

      Shah, Chinmay; Wies, Richard W.; Al-Badri, Maher; Huang, Daisy; Cicilio, Phylicia (2022-05)
      Integration of power electronic converter-based distributed energy resources (DERs) in electric power distribution networks is growing exponentially with the recent interest in reducing carbon emissions from fossil fuel-based generation. As the contribution of renewable energy sources in the DER mix continues to increase, so does the incorporation of battery energy storage systems and other controllable loads to compensate for the high variability and uncertainty in the generation from renewable DERs and grid demand. Strategies for increasing the contribution of renewable energy sources and using reserves to accommodate for variations and uncertainty in generation and load include distributed optimal power flow (OPF) methods and improved forecasting. This work proposes a co-optimization of power flow and flexibility reserves, executed on a private blockchain for security, solved using a parameterized deterministic method based on semi-distributed architecture and alternating direction method of multipliers (ADMM) based distributed architecture that addresses uncertainty and enhances the flexibility of the distribution network. However, ADMM guarantees convergence only for strictly convex problems and hence a relax-and-fix heuristic algorithm is proposed in co-ordination with ADMM to solve the OPF problem, which is non-convex in nature. Also, an accurate short-term load forecasting algorithm is essential to reduce the uncertainty in the dispatch results using the OPF algorithm. In this work, a short-term residential load forecasting algorithm is proposed using a two-stage stacked long short-term memory network-based recurrent neural network and Hampel filter to address this issue. All the proposed algorithms are tested using different case studies. Results demonstrate that the proposed algorithms reduce the impact of uncertainty in the distribution network, automate scheduling flexibility reserve and minimize its cost, reduce the OPF execution time using a distributed architecture, and produce residential load forecast with a significantly lower prediction error.