Duke University Wind Symphony and KSU Wind Ensemble, The Duke Blue Devils meet the KSU Owls

KSU School of Music presents The Duke Blue Devils meet the KSU Owls featuring Duke University Wind Symphony and KSU Wind Ensemble.https://digitalcommons.kennesaw.edu/musicprograms/1284/thumbnail.jp

Processor Verification Using Efficient Reductions of the Logic of Uninterpreted Functions to Propositional Logic

The logic of equality with uninterpreted functions (EUF) provides a means of abstracting the manipulation of data by a processor when verifying the correctness of its control logic. By reducing formulas in this logic to propositional formulas, we can apply Boolean methods such as Ordered Binary Decision Diagrams (BDDs) and Boolean satisfiability checkers to perform the verification. We can exploit characteristics of the formulas describing the verification conditions to greatly simplify the propositional formulas generated. In particular, we exploit the property that many equations appear only in positive form. We can therefore reduce the set of interpretations of the function symbols that must be considered to prove that a formula is universally valid to those that are ``maximally diverse.'' We present experimental results demonstrating the efficiency of this approach when verifying pipelined processors using the method proposed by Burch and Dill.Comment: 46 page

Characterizing small-scale migration behavior of sequestered CO2 in a realistic geological fabric

For typical reservoir conditions, buoyancy and capillary forces grow dominant over viscous forces within a few hundred meters of the injection wells as the pressure gradient due to injection decreases, resulting in qualitatively different plume migration regimes. The migration regime depends on two factors: the capillary pressure of the leading edge of the plume and the range of threshold entry pressures within the rock at the leading edge of the plume. A capillary channel regime arises when these two factors have the same magnitude. Flow patterns within this regime vary from finger-like structures with minimal rock contact to back-filling structures with compact volumes of saturation distributed between fingers. Reservoir heterogeneity is one of the principal factors influencing CO2 migration pathway in the capillary channel regime. Here we characterize buoyancy-driven migration in a natural 2D geologic domain (1 m × 0.5 m peel from an alluvium) in which sedimentologic heterogeneity has been resolved at sub-millimeter (depositional) resolution. The relevant features of the heterogeneity are grain size distribution, which determines the mean and range of threshold pressures and correlation lengths of threshold pressures in horizontal and vertical directions. The relevant physics for this migration regime is invasion percolation, and simulations indicate that CO2 migrates through the peel in a few narrow pathways which cannot be captured by conventional coarse-grid simulations. The storage efficiency of the capillary channel regime would be low and consequently CO2 would also migrate greater distances than expected from models or simulations that neglect the capillary channel flow regime.Bureau of Economic Geolog

Quantifying Thermally Driven Fracture Geometry During CO2 Storage

AbstractThe desired lifetime for CO2 injection for sequestration is several decades at a high injection rate (up to 10 bbl/min or 2,400 tons/day per injector). Government regulations and geomechanical design constraints may impose a limit on the injection rate such that, for example, the bottomhole pressure remains less than 90% of the hydraulic fracture pressure. Despite injecting below the critical fracture pressure, fractures can nevertheless initiate and propagate due to a thermoelastic stress reduction caused by cool CO2 encountering hot reservoir rock.Here we develop a numerical model to calculate whether mechanical and thermal equilibrium between the injected CO2 and the reservoir evolves, such that fracture growth ceases. When such a condition exists, the model predicts the corresponding fracture geometry and time to reach that state.The critical pressure for fracture propagation depends on the thermoelastic stress, a function of rock properties and the temperature difference between the injected fluid and the reservoir (ΔT). Fractures will propagate as long as the thermoelastic stress and the fluid pressure at the fracture tip exceed a threshold; we calculate the extent of a fracture such that the tip pressure falls below the thermoelastically modified fracture propagation pressure. Fracture growth is strongly dependent upon the formation permeability, the level of injection pressure above fracture propagation pressure, and ΔT

Lee Barnett and Steven Bryant in a Joint Senior Composition Recital

This is the program for the joint senior composition recital of Lee Barnett and Steven Bryant. This recital took place on April 14, 1994, in the McBeth Recital Hall in the Mabee Fine Arts Center

Pressure perturbations from geologic carbon sequestration: Area-of-review boundaries and borehole leakage driving forces

We investigate the possibility that brine could be displaced upward into potable water through wells. Because of the large volumes of CO2 to be injected, the influence of the zone of elevated pressure on potential conduits such as well boreholes could extend many kilometers from the injection site—farther than the CO2 plume itself. The traditional approach to address potential brine leakage related to fluid injection is to set an area of fixed radius around the injection well/zone and to examine wells and other potentially open pathways located in the “Area-of-Review” (AoR). This suggests that the AoR needs to be defined in terms of the potential for a given pressure perturbation to drive upward fluid flow in any given system rather than on some arbitrary pressure rise. We present an analysis that focuses on the changes in density/salinity of the fluids in the potentially leaking wellbore.Bureau of Economic Geolog

Semi-analytical model to determine perforation interval for secure CO2 storage in saline aquifers

AbstractDue to density difference between injected CO2 and in-situ brine, the pressure difference between wellbore and formation varies with depth in a CO2 injection well. Consequently the flux distribution along a vertical well is not uniform during the early stages of injection. For injection rates below a certain threshold, this can lead to only a fraction of the perforations contributing to injection. Generally this reduces the efficiency of CO2 immobilization by dissolution in brine and by residual trapping because less volume of rock and brine comes in contact with injected CO2. Thus for injection rates below the threshold, optimization of the length of the perforated interval is required to maximize trapping. We describe a semi-analytical algorithm that finds the optimum interval of injection for a given flow rate so that all the perforations contribute throughout the injection period. Although bottomhole pressure rises while injecting in smaller perforation interval, the greater mobility of the CO2 phase upstream of the drying front reduces this increase and enables the use of smaller interval. In the case of a horizontal well, the length of well plays an important role in determining the CO2 trapping. The two competing effects, trapping along the well length and along lateral direction, determine the optimum well length required. Greater well length increases the trapping in direction of well path but reduces in lateral direction because of the ratio of gravity forces to viscous forces becomes larger. Thus dominance of either of these competing effects and cost of drilling determine optimal well length. This study illustrates the effect of different injection strategies on multiple objectives of CO2 sequestration including maximizing trapping and minimizing leakage potential. We find that the benefits of a strategy to maximize injectivity may be offset by less CO2 entering secure modes of storage