Tadeusz Wiktor Patzek

The Visible, Sustainable Farm: A Comprehensive Energy Analysis of a Midwestern Farm

The Sunshine Farm, in central Kansas, offers a unique data set detailing all the inputs and outputs of a farming project intended to be based, as much as possible, on solar energy. Such a complete and detailed data set, encompassing more than 1.25 M data points for an 85-ha, 7-year project, has never before been compiled for any farm. The data show that important energy inputs that have thus far been left out of existing farm energy efficiency estimates, with implications for biofuels and other biomass for energy technologies. The SSF achieved energy efficiencies superior to conventional agriculture while maintaining soil health and delivering more nutritious, organic products. A first-ever analysis of the energy efficiency of horse traction shows that horses are significantly less energy efficient and much less labor efficient than tractors, although the horses in the study were clearly underutilized. An analysis of the farm removing all inputs and outputs relevant to the horses shows that without horses the Sunshine Farm would have been competitive with conventional energy efficiencies even taking into account the farms higher labor inputs and small size.

Predicting Relative-Permeability Curves Directly From Rock Images

The objective of this study is determination of relative per meability curves from an analysis of the pore space geometry. The main assumptions are that the capillary pressure determines the fluid distribution and the rock is water-wet. Maximal inscri bed spheres computations characterize the portion of the pore space occupied by each fluid at a given saturation. Numerical solution of the Stokes equations evaluates the pore-scale flow field, which is avera ged to estimate the permeability to each fluid. The computed r elative permeability curves are in good agreement with published data. The input for the proposed procedure can be either a computer tomography image of a sample of the rock of interest, or a computergenerated image based on depositional simulations. Partitioning of the entire domain into parts significantly improve s the convergence and makes feasible implementation of the computational procedure on a desktop computer. The stability of the results with respect to the choice of computational parameters makes the proposed method suitable for routine applications. The model admits generalizations relaxing the requirement of water wetness of the rock. This model can be applied to evaluate the evolution of the rock flow p roperties under deformation, damage, mineral dissolution and precipitation.

Micromechanics of Hydrate Dissociation in Marine Sediments by Grain-Scale Simulations

We seek to quantify the impact of hydrate dissociation on the strength of hydrate-bearing sediments. Dissociation of gas-hydrates in marine sediments converts the solid hydrate structure into liquid water and gas. Together with the associated pore pressure increase, this process reduces the stiffness of the sediments, which may fracture or be fluidized. If sediment failure occurs, seafloor subsidence and landslides can severely damage offshore infrastructure. To evaluate the mechanical properties of a sediment sample, we simulate loading of a disordered pack of spherical grains by incremental displacements of its boundaries. The deformation is described as a sequence of equilibrium configurations. Each configuration is characterized by a minimum of the total potential energy. This minimum is computed using a modification of the conjugate gradient algorithm. We verify our model against published data from experiments on glass beads. Our simulations capture the nonlinear, path-dependent behavior of granular materials observed in experiments. Hydrates are modeled as load-bearing solid particles within the pores. To simulate the consequences of dissociation, we reduce the solid fraction by shrinking the hydrate grains. The effect of the associated excess pore pressure is modeled by isotropic compression of the solid grains, and reduction in macroscopic effective stress. Weakening of the sediment is quantified as a reduction of the effective elastic moduli.

The Future of California's Oil Supply

Once an oil exporter, California now depends on imports for more than 60% of its oil supply. This paper examines the oil production outlook for each of California’s major oil sources, including California itself. Oil production trends, published geological and engineering reports, and proposed developments in Californias supply area are reviewed to define supply trends, especially for the medium-to-heavy, sour crudes that are processed in Californias refineries. Refinery upgrading capacity is already highly developed in California, thus it is assumed that a competitive advantage in heavy, sour crudes will continue, although refining heavy oil releases more carbon dioxide. About a quarter of Californias imports are from Alaska, the rest from foreign sources including Saudi Arabia, Ecuador and Iraq. Before foreign sources became so important, Californias refining industry processed Californias own crudes and Alaska’s North Slope crude. Like those crudes, oil from northern Saudi Arabia, southeast Iraq, and Ecuador is also sour and medium to heavy, ranging from 16 to 35° API and from 2 to more than 3% sulfur by weight. By far the most important sour crude development in Californias supply area is Saudi Arabias 900,000 BOPD Manifa project, originally slated for completion in 2011 but now facing delays. Manifa contains oil that ranges from 26 to 31° API and from 2.8 to 3.7% sulfur. Over the longer term, Alaska will continue to play an important supply role if the Chuckchi and Beaufort Seas live up to expectations. Middle East production is not increasing, yet oil cargoes from the Middle East have to pass growing Asian markets to reach California. Alaska and Mexico also supply oil to the Pacific Basin, but are facing production declines. The effect of rising Asian demand on Pacific Basin oil markets is already visible, with significant amounts of oil coming to California from Atlantic Basin sources such as Angola, Brazil, and Argentina. The US West Coast pipeline system is separate from the integrated East Coast, Gulf Coast and Midwest system, so energy security issues for the West Coast may differ from those of the country as a whole. There are policy options that could affect Californias oil supply security, including increased oil development in Alaska or offshore California, development of additional oil pipeline outlets on Canadas Pacific Coast or substituting natural gas for oil if possible. All of these policy options are currently the subject of political debate.

Exact solutions in a model of vertical gas migration

This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding atmospheric emissions of carbon dioxide and consequent global warming. One of the key questions regarding the feasibility of this technology is the potential rate of leakage out of the primary storage formation. We seek exact solutions in a model of gas flow driven by a combination of buoyancy, viscous and capillary forces. Different combinations of these forces and characteristic length scales of the processes lead to different time scaling and different types of solutions. In the case of a thin, tight seal, where the impact of gravity is negligible relative to capillary and viscous forces, a Ryzhik-type solution implies square-root of time scaling of plume propagation velocity. In the general case, a gas plume has two stable zones, which can be described by travelling-wave solutions. The theoretical maximum of the velocity of plume migration provides a conservative estimate for the time of vertical migration. Although the top of the plume has low gas saturation, it propagates with a velocity close to the theoretical maximum. The bottom of the plume flows significantly more slowly at a higher gas saturation. Due to local heterogeneities, the plume can break into parts. Individual plumes also can coalesce and from larger plumes. The analytical results are applied to studying carbon dioxide flow caused by leaks from deep geological formations used for CO2 storage. The results are also applicable for modeling flow of natural gas leaking from seasonal gas storage, or for modeling of secondary hydrocarbon migration.