School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Multiphysics Investigation of Wellbore Mixing and Storage Effects on Groundwater Pumping and Sampling 

By Yu He

Advisors:

Dr. Jian Luo (CEE)

Dr. Haiying Huang (CEE)

Committee Members:   Dr. Kevin A. Haas (CEE),
Dr. Alexander Robel (EAS), Dr. Chris CK Lai (CEE) 

Date and Time:  Friday, March 1st, 8:00 AM - 10 AM

Location: Mason Building, Room 222, Teams: Teams Meeting

Two fundamental processes significantly influence the hydraulic behavior of an abstraction well-aquifer system: well storage and wellbore mixing, which involve the interaction between vertical casing flow, solute transport in the wellbore, and horizontal aquifer inflow. Improved understanding of these processes has profound implications for well hydraulics, well testing analysis, production, and groundwater sampling. This thesis develops multiphysics models integrating wellbore flow and transport with porous media flow to explore their coupled effects during groundwater pumping and sampling. Analytical solutions are devised, offering new insights into these processes. Laboratory tank experiments were conducted to assess a novel groundwater sampling approach.
For high pumping rates, involving high Reynolds numbers in the wellbore and adjacent formation, turbulent flow in the wellbore and non-Darcy flow in the formation are considered. The analysis encompasses drawdown in the wellbore and formation, water flow ratio, and a novel nonlinearity ratio characterizing the disparity between formation conductivity and equivalent nonlinear flow conductivity. A critical distance is identified to delineate nonlinear and linear formation flow regions during quasi-steady state. The wellbore flow regime significantly influences near-well formation flow, leading to increased drawdown and uneven stress at the screen. 
At low pumping rates, characterized by low Reynolds numbers, laminar flow and solute transport in the wellbore and Darcy flow in the formation are considered. A comprehensive evaluation of the combined impact of well storage and wellbore mixing on various sampling strategies is conducted. An analytical solution for pumped sample concentration is proposed, sensitive to both stratified and homogeneous formation conditions. Wellbore mixing emerges as the limiting factor for sample stabilization in high-yield aquifers or wells with longer residence times.
Existing groundwater sampling methods are found inefficient in low-yield aquifers. To address this, a novel two-stage pumping strategy, the high-stress low-flow (HSLF) approach, is introduced, complete with mathematical derivations and practical graphical tools. The HSLF approach defines a desired sampling window wherein groundwater inflow reaches its peak. Experimental validation confirms the numerical simulations and proposed mathematical models. Light attenuation analysis and pressure data capture the wellbore mixing process and depletion of well storage, respectively. A drawdown solution delineates the early transient state and well storage effect in the laboratory-scaled flow tank. The experimental results and analytical model offer a comprehensive analysis of pumping system dynamics and tools for determining hydraulic properties in laterally bounded confined aquifers. Notably, the HSLF approach yields pumped samples that accurately and rapidly reflect in situ groundwater conditions, outperforming conventional sampling strategies.