A higher-order finite element reactive transport model for unstructured and fractured grids.

This work presents a new reactive transport framework that combines a powerful geochemistry engine with advanced numerical methods for flow and transport in subsurface fractured porous media. Specifically, the PhreeqcRM interface (developed by the USGS) is used to take advantage of a large library of equilibrium and kinetic aqueous and fluid-rock reactions, which has been validated by numerous experiments and benchmark studies. Fluid flow is modeled by the Mixed Hybrid Finite Element (FE) method, which provides smooth velocity fields even in highly heterogenous formations with discrete fractures.

Geometry-Driven Detection, Tracking and Visual Analysis of Viscous and Gravitational Fingers.

Viscous and gravitational flow instabilities cause a displacement front to break up into finger-like fluids. The detection and evolutionary analysis of these fingering instabilities are critical in multiple scientific disciplines such as fluid mechanics and hydrogeology. However, previous detection methods of the viscous and gravitational fingers are based on density thresholding, which provides limited geometric information of the fingers.

Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study.

Horizontal drilling and hydraulic fracturing have enhanced unconventional hydrocarbon recovery but raised environmental concerns related to water quality. Because most basins targeted for shale-gas development in the USA have histories of both active and legacy petroleum extraction, confusion about the hydrogeological context of naturally occurring methane in shallow aquifers overlying shales remains. The Karoo Basin, located in South Africa, provides a near-pristine setting to evaluate these processes, without a history of conventional or unconventional energy extraction.

Numerical Modeling of Methane Leakage from a Faulty Natural Gas Well into Fractured Tight Formations.

Horizontal drilling and hydraulic fracturing have enabled hydrocarbon recovery from unconventional reservoirs, but led to natural gas contamination of shallow groundwaters. We describe and apply numerical models of gas-phase migration associated with leaking natural gas wells. Three leakage scenarios are simulated: (1) high-pressure natural gas pulse released into a fractured aquifer; (2) continuous slow leakage into a tilted fractured formation; and (3) continuous slow leakage into an unfractured aquifer with fluvial channels, to facilitate a generalized evaluation of natural gas transport from faulty natural gas wells.

Impacts of Methane on Carbon Dioxide Storage in Brine Formations.

In the context of geological carbon sequestration (GCS), carbon dioxide (CO ) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH ). In this multicomponent multiphase displacement process, CO competes with CH in terms of dissolution, and CH tends to exsolve from the aqueous into a gaseous phase. Because CH has a lower viscosity than injected CO , CH is swept up into a 'bank' of CH -rich gas ahead of the CO displacement front.

Dissolution Trapping of Carbon Dioxide in Heterogeneous Aquifers.

The geologic architecture in sedimentary reservoirs affects the behavior of density-driven flow and the dispersion of CO-rich brine. The spatial organization and connectivity of facies types play an important role. Low-permeability facies may suppress fingering and reduce vertical spreading, but may also increase transverse mixing.

Critical Dynamics of Gravito-Convective Mixing in Geological Carbon Sequestration.

When CO is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees.

Geographic axes and the persistence of cultural diversity.

Jared Diamond's Guns, Germs, and Steel [Diamond J, (1997) Guns, Germs, and Steel (WW Norton, NY)] has provided a scientific foundation for answering basic questions, such as why Eurasians colonized the global South and not the other way around, and why there is so much variance in economic development across the globe. Diamond's explanatory variables are: (i) the susceptibility of local wild plants to be developed for self-sufficient agriculture; (ii) the domesticability of large wild animals for food, transport, and agricultural production; and (iii) the relative lengths of the axes of continents with implications for the spread of human populations and technologies. This third "continental axis" thesis is the most difficult of Diamond's several explanatory factors to test, given that the number of continents are too few for statistical analysis.