Date of Award

December 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

Weon Shik Han

Committee Members

Timothy Grundl, Dyanna Czeck

Keywords

CO2 Sequestration, Fault Leakage, Multiphase Flow, Natural Analogue, Numerical Modeling, Wellbore Leakage

Abstract

This study investigated a natural analogue for CO2 leakage near Green River, Utah, aiming to understand the influence of various factors on CO2 leakage and to reliably predict underground CO2 behavior after injection for geologic CO2 sequestration. Advective, diffusive, and eruptive characteristics of CO2 leakage were assessed via a soil CO2 flux survey and numerical modeling. The field results show anomalous CO2 fluxes (> 10 g m-2 d-1) along the faults, particularly adjacent to CO2-driven cold springs and geysers (e.g., 36,259 g m-2 d-1 at Crystal Geyser), ancient travertines (e.g., 5,917 g m-2 d-1), joint zones in sandstone (e.g., 120 g m-2 d-1), and brine discharge zones (e.g., 5,515 g m-2 d-1). Combined with similar isotopic ratios of gas and progressive evolution of brine chemistry at springs and geysers, a gradual decrease of soil CO2 flux from the Little Grand Wash (LGW; ~36,259 g m-2 d-1) to Salt Wash (SW; ~1,428 g m-2 d-1) fault zones reveals the same CO2 origin and potential southward transport of CO2 over 10-20 km.

The numerical simulations exhibit lateral transport of free CO2 and CO2-rich brine from the LGW to SW fault zones through the regional aquifers (e.g., Entrada, Navajo, Kayenta, Wingate, White Rim). CO2 travels predominantly as an aqueous phase (Xco2=~0.045) as previously suggested, giving rise to the convective instability that further accelerates CO2 dissolution. While the buoyant free CO2 always tends to ascend, a fraction of dense CO2-rich brine flows laterally into the aquifer and mixes with the formation fluids during upward migration along the fault. The fault always enhances advective CO2 transport regardless of its permeability (k). However, only low-k fault prevents unconditional upright migration of CO2 and induces fault-parallel movement, feeding the northern aquifers with more CO2. Low-k fault also impedes lateral southward fluid flow from the northern aquifers, developing anticlinal CO2 traps at shallow depths (<300 m). The regional k of the LGW fault in which CO2 flux coincides with the field spatial variation is estimated between 0.01≤kh<0.1 md and 0.5≤kv<1 md. The anticlinal trap serves as an essential fluid source and conducive environment for intensifying eruption at Crystal Geyser. Geyser-like discharge in the simulations sensitively responds to varying well permeability and radius, and CO2 recharge rate. Indeed, the cycling behavior of wellbore CO2 leakage turns into a constant discharge with time, indicating the potential switch of Crystal Geyser to a CO2-driven cold-water spring or even fumarole.

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