Confined Space Dissertation

Abstract

This work develops a rigorous method for including confinement effects in fluid modeling. This method was implemented into phase modeling and compositional reservoir simulation to show the impacts of tight media on hydrocarbon phase behavior and production. The rigorous aspect of this method improves upon current methods of incorporating confinement effects in both fluid modeling and reservoir simulation. It is particularly useful for porous media with small pores, where the ratio of medium surface area to fluid volume and fluid-to-rock interaction are significant. The proposed model utilizes the Peng-Robinson equation of state coupled with the Young-Laplace equation for capillary pressure. The interfacial tension is determined using the parachor model, which is dependent on phase compositions and molar volumes. Capillary pressure is therefore implemented within the vapor-liquid equilibrium (VLE) calculations. Contact angle is an input and can be updated as a temperature-dependent function. When implemented inside the VLE loop, calculation time is minimally impacted, making this a very efficient method. Vapor-liquid equilibrium using this method for small pores is validated by modeling cases presented in published literature. These published data are obtained either experimentally or by using molecular simulation. In all cases, the model presented in this work is able to closely match phase behavior, showing a decrease in bubble point pressure, and an increase in dew point pressure. Changes in saturation pressure approach zero as the mixture critical point is approached. Implementation of this method into compositional reservoir simulation shows that confinement generally increases oil and gas production from tight oil reservoirs and generally decreases oil and gas production from tight gas condensate reservoirs, compared with the traditional bulk compositional simulators. Simple cases of a reservoir cell can be modeled with capillary pressure using a constant-composition expansion or constant-volume depletion method. This results in a capillary pressure curve as a function of liquid saturation. With these curves, relative permeability can be predicted by integration of the reciprocal of the square of capillary pressure. Reservoir simulation of an Eagle Ford reservoir fluid at various initial pressures shows the impact of capillary pressure and relative permeability on production. At high initial reservoir pressure, oil/gas relative permeability is insignificant, but capillary pressure still significantly impacts oil production. At lower initial pressure, capillary pressure and oil/gas relative permeability both significantly impact production.

Stimpson, Brian C (2017). Impacts of Confined Space on Production from Tight Reservoirs. Master's thesis, Texas A & M University. Available electronically from http://hdl.handle.net/1969.1/161330.

Humidity control in confined building spaces using a liquid desiccant dehumidifier

Dayu Dong, University of Nebraska - Lincoln

Abstract

This dissertation investigates the application of a liquid desiccant dehumidifier system in confined building spaces. The proposed dehumidifier system controls the humidity ratio of the confined space when a large amount of moisture is released, and uses ambient space air for regeneration when the spaces produce no moisture. The generated moisture air during the regeneration period can be discharged through continuous exhaust ventilation. ^ In the dissertation, the physical system design is described and dehumidifier performance models and CFD models are integrated and developed. Numerical simulations were conducted to compare the results of a conventional ventilation system and a dehumidifier system. ^ The results of the simulations show that the dehumidifier system reduced moisture condensation by 24.0% over a conventional exhaust ventilation system. It was also found that the configurations of the confined space and dehumidifier, e.g., the locations of the inlet air, exhaust air and moisture source, significantly impacted the space air humidity ratio and temperature distributions. ^ The theoretical analysis in the feasibility investigation suggests that an optimal dehumidifier system reduces moisture condensation and saves energy. Thus, the system optimizations are achieved by three approaches: optimal dehumidifier design parameters, improved dehumidifier location, and optimal regeneration period. ^ The results of the optimizations show that an improved dehumidifier location can reduce moisture condensation by 33.1% over the original dehumidifier location in the feasibility investigation. In addition, use of an optimal reheat desiccant temperature can reduce the regeneration period by 16.0% and the total performance period by 12.5%. ^ Yearly energy consumption and cost were compared between a base ventilation system and an optimal dehumidifier system for a bathroom in a hotel at two locations of Miami and Omaha. The comparisons were conducted for both systems with the same amount of accumulated condensation on the surfaces of the space. The total yearly electricity energy consumption in an optimal dehumidifier system can be saved by 63.7% in Omaha and 65.2% in Miami. The heating consumption can be saved by 66.7% in Omaha and 66.7% in Miami. The average yearly energy cost saving is around 65.5%. ^

Subject Area

Engineering, Mechanical

Recommended Citation

Dong, Dayu, "Humidity control in confined building spaces using a liquid desiccant dehumidifier" (2005). ETD collection for University of Nebraska - Lincoln. AAI3199694.
https://digitalcommons.unl.edu/dissertations/AAI3199694

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