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Wellbore Stability In Water-Sensitive Shales, Qingfeng Tao

Theses and Dissertations

Wellbore instability is a widespread problem, especially when drilling in deep, low strength shale formations at high temperature and pressure. The instability can be caused by the high compressive effective stress or tensile stress due to the stress concentration and pore pressure increase while drilling. In addition to the in-situ stress and shale strength, shale instability is affected by drilling mud properties including mud weight, temperature and salinity. To assess wellbore stability in these situations, Diek and Ghassemi (2004) developed a non-linear coupled chemo-poro-thermoelasticity theory. The linearized version of the theory allows one to analytically investigate the coupled impacts of …

Modeling Groundwater Denitrification By Ferrous Iron Using Phreeqc, Tedros Tesfay

Theses and Dissertations

Nitrate is one of the most common groundwater contaminants, and ingesting it leads to potential health risks. Denitrification, the only effective process to eliminate nitrate, is limited by the abundance of biologically available electron donors. Thus, understanding the natural denitrification capacity of aquifers, through the analysis of all the major electron donors, is essential.

A better way to estimate groundwater denitrification reactions is to compute the mass balance of the redox sensitive species. The University of North Dakota (UND) denitrification team installed mesocosms (ISMs) to understand the fate of nitrate in field conditions. Accordingly, the team has shown the significant …

Evaluating Surface Area-Basin Volume Relationships For Prairie Potholes, Mike A. Davis

Theses and Dissertations

Establishing a relationship between surface area and volume of prairie potholes provides a simple method to estimate changes in water storage across the landscape. Applications include better prediction of floods and improved design for wetland restoration. Length, width, depth, surface area, and volumes were surveyed for eighty two potholes within the upper Turtle River watershed which lies sixty kilometers west of Grand Forks, ND. These data were used to determine the relationship and uncertainty between pothole surface and volume. Chi squared tests defined distributions of each variable. F and T statistical tests resolved similarities in variance and mean. The eighty …