Terizhandur S. Ramakrishnan

3-D carbon nanotube structures used as high performance catalyst for oxygen reduction reaction.

We report a high performance oxygen reduction reaction (ORR) catalyst based on vertically aligned, nitrogen-doped carbon nanotube (VA-NCNT) arrays. Characterization in conditions analogous to the operation of a polymer electrolyte membrane fuel cell show ORR taking place on the catalyst at a favorable reduction potential with a superior current density and greater rate constant.

Relative Permeability Experiments of Carbon Dioxide Displacing Brine and Their Implications for Carbon Sequestration

To mitigate anthropogenically induced climate change and ocean acidification, net carbon dioxide emissions to the atmosphere must be reduced. One proposed option is underground CO2 disposal. Large-scale injection of CO2 into the Earths crust requires an understanding of the multiphase flow properties of high-pressure CO2 displacing brine. We present laboratory-scale core flooding experiments designed to measure CO2 endpoint relative permeability for CO2 displacing brine at in situ pressures, salinities, and temperatures. Endpoint drainage CO2 relative permeabilities for liquid and supercritical CO2 were found to be clustered around 0.4 for both the synthetic and natural media studied. These values indicate that relative to CO2, water may not be strongly wetting the solid surface. Based on these results, CO2 injectivity will be reduced and pressure-limited reservoirs will have reduced disposal capacity, though area-limited reservoirs may have increased capacity. Future reservoir-scale modeling efforts should incorporate sensitivity to relative permeability. Assuming applicability of the experimental results to other lithologies and that the majority of reservoirs are pressure limited, geologic carbon sequestration would require approximately twice the number of wells for the same injectivity.

Analysis and computation of gravity-induced migration in porous media

Motivated by the problem of gravity segregation in an inclined porous layer, we present a theoretical analysis of interface evolution between two immiscible fluids of unequal density and mobility, both in two and three dimensions. Applying perturbation theory to the appropriately scaled problem, we derive the governing equations for the pressure and interface height to leading order, obtained in the limit of a thin gravity tongue and a slightly dipping bed. According to the zeroth-order approximation, the pressure profile perpendicular to the bed is in equilibrium, a widely accepted assumption for this class of problems. We show that for the inclined bed two-dimensional problem, in the reference frame moving with the mean gravity-induced advection velocity, the interface motion is dictated by a degenerate parabolic equation, different from those previously published. In this case, the late-time behaviour of the gravity tongue can be derived analytically through a formal expansion of both the solution and its two moving boundaries. In three dimensions, using a moving coordinate along the dip direction, we obtain an elliptic―parabolic system of partial differential equations where the fluid pressure and interface height are the two dependent variables. Although analytical results are not available for this case, the evolution of the gravity tongue can be investigated by numerical computations in only two spatial dimensions. The solution features are identified for different combinations of dimensionless parameters, showing their respective influence on the shape and motion of the interface.

Asymptotic solution of a nonlinear advection-diffusion equation

We carry out an asymptotic analysis as t → ∞ for the nonlinear advection-diffusion equation, ∂ t u = 2αu∂ x u + ∂ x (u∂ x u), where α is a constant. This equation describes the movement of a buoyancy-driven plume in an inclined porous medium, with α having a specific physical significance related to the bed inclination. For compactly supported initial data, the solution is characterized by two moving boundaries propagating with finite speed and spanning a distance of O(√t). We construct an exact outer solution to the PDE that satisfies the right boundary condition. The vanishing condition at the left boundary is enforced by introducing a moving boundary layer, for which we obtain a closed-form expression. The leading-order composite solution is uniformly correct to O(1/√t). A higher-order correction to the inner and the composite solutions is also derived analytically. As a result, we obtain late-time asymptotic expansions for the two moving boundaries, correct to O(1), as well as a composite solution correct to O(1/t). The findings of this paper are illustrated and verified by numerical computations.

Determining carbon sequestration injection potential at a site-specific location within the Ohio River Valley region

Publisher Summary This chapter presents results from the initial field investigations from the site-characterization effort. Depending upon the geology and the reservoir characteristics, the ultimate objective for this project is to progress towards demonstration of CO2 injection in deep geological reservoirs in the region. Towards this objective, an effort was made to ensure that, if a decision is made to proceed to an injection phase, the current test well will be able to meet the relevant regulatory criteria. The results given in the chapter pertain to the assessment of the injectivity and the storage capacity. Containment evaluation is also a part of the assessment. The research presented here provides a protocol for similar characterization in deeper sedimentary basin elsewhere in the world, especially those where pre-existing information is sparse. While many of the techniques used are similar to those used in oil and gas exploration, it is noteworthy that the testing objectives are very different, with a greater emphasis on the evaluation of containment and injection potential, rather than on the presence and quantification of oil/gas reserves, and on ensuring that the drilling, testing, and well design comply with underground injection regulations. There is also a greater emphasis on collecting information that may be needed for allaying possible stakeholder concerns about the risks from carbon sequestration technologies.

Late-time asymptotic solution of nonlinear advection-diffusion equations with equal exponents

We derive the late-time asymptotic solution of a nonlinear advectiondiffusion equation, ut = [α/(q − 1)](u)x + (1/q)(u)xx, where α = 0 and q > 2. The equation is a more general form of the purely quadratic nonlinearity for advection and diffusion considered previously. For initial conditions with compact support, the solution has left and right moving boundaries, the distance between which is the width of the “plume”. We show the width to grow as t, with a constant correction term. The outer solution is dominated by the nonlinear advective term, the leading-order solution of which is shown to satisfy the partial differential equation and the right boundary condition exactly, but with a t-dependent shifted argument. To satisfy the left boundary of vanishing plume thickness, a boundary layer is introduced, for which the inner solution may be obtained up to second order, again by using a shifted coordinate with respect to the wetting front. A leading-order composite solution for u, uniformly correct to O(1/t), is obtained. The first and second-order terms are correct to O((1/t) ln t) and O(1/t) respectively. The composite second-order correction involves an arbitrary constant, implying its dependence on an unknown initial condition. Numerical results that agree with the analytical solutions are given along with an expression for the unknown constant computed with an impulse initial data.

Comprehensive Reservoir Characterization Through Data Integration and Numerical Single Well Simulation

Reservoir heterogeneity, single and multi-phase formation properties dictate well productivity, reservoir performance and management strategy. Cores, open hole logs, formation testers, pressure transient tests, and production logs are usually used to estimate the reservoir heterogeneity and quantify the single and multi-phase formation properties. The results obtained from these techniques are utilized in reservoir simulations to assess the reservoir performance and optimize the reservoir production.