Parity violating target asymmetry in electron - proton scattering

We analyze the parity-violating (PV) components of the analyzing power in elastic electron-proton scattering and discuss their sensitivity to the strange quark contributions to the proton weak form factors. We point out that the component of the analyzing power along the momentum transfer is independent of the electric weak form factor and thus compares favorably with the PV beam asymmetry for a determination of the strangeness magnetic moment. We also show that the transverse component could be used for constraining the strangeness radius. Finally, we argue that a measurement of both components could give experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.

Investigation of the VAPEX Process Using CT Scanning and Numerical Simulation

Abstract The "VAPEX" process, a solvent analogue of Steam Assisted Gravity Drainage, has attracted considerable attention as a recovery method for heavy oil. However, to date, there are still many questions about the nature and magnitude of basic process mechanisms, and whether the process can produce economic oil rates. The experiments discussed in this paper were aimed at quantifying some of the basic mechanisms, in particular the dispersive mixing mechanism. We have performed a series of topdown solvent injection experiments under varying conditions, utilizing a CT scanner to monitor fluid movements. All of the displacements we have observed are gravity-unstable in the early stages, and characterized by viscous fingering of the solvent into the 5,500 cP oil. After solvent breakthrough, the displacements become stable, dominated by a single solvent finger which has many of the features of a VAPEX solvent chamber. The "mixing parameter" we infer for these experiments using the Butler/Mokrys analytic model is higher than that reported for Hele-Shaw VAPEX experiments. An analysis of localized fluid velocities in the experiments using numerical simulation shows that the enhanced mixing parameter can be understood as a consequence of convective dispersion in the porous medium. By adjusting the amount of physical dispersion, the simulations can match breakthrough time, post-breakthrough oil rates, and the general character of the fingering. A novel type of "quasi-pore scale" simulation grid appears to provide advantages in simulating the unstable period at the beginning of the displacements. Introduction Compared with steam-based processes such as Steam Assisted Gravity Drainage (SAGD) for recovery of heavy oil, solventbased processes offer the possibility of reduced energy consumption and greenhouse gas production. However, they are mechanistically complex, and questions remain regarding their expected performance. To date, no field data are publicly available to answer these questions. One solvent-based process that has been proposed is the Vapour Extraction (VAPEX) process(1, 2). This solvent analogue of SAGD utilizes gravity as the driving agent, and solvent dilution of the heavy oil as the mobilization mechanism. The concept of the process is illustrated in Figure 1. A practical, solvent-based recovery process will depend for its success on the interplay of a number of phenomena. Some of the most important of these are: diffusion/dispersion, viscous fingering, capillary-driven mixing (in the case of a gaseous solvent), and the effects of reservoir heterogeneity. The first three are accessible for study in the laboratory, and understanding their interplay at the laboratory scale is a first step toward predicting their effects in a field process. Numerical simulation is required both to extrapolate laboratory experience to the field scale, and to incorporate the effects of reservoir heterogeneity. The study described in this paper addresses the phenomena of diffusion/dispersion and viscous fingering based on a series of laboratory experiments, combined with numerical simulation. Our initial experiments utilized a liquid solvent; therefore capillary mixing effects were absent. Future work will extend the results to gaseous solvents. </jats:sec

Viscous Fingering Effects in Solvent Displacement of Heavy Oil

Abstract A number of solvent-based processes for the recovery of heavy oil have been proposed in recent years. One of the phenomena that characterizes all such processes, to varying degrees, is viscous fingering. This paper describes the results of a combined experimental/simulation study aimed at characterizing viscous fingering under conditions typical of heavy oil recovery (very high ratios of oil to solvent viscosity). The study also sheds light on other phenomena that are part of such processes. We describe a set of four experiments carried out in heavy oil saturated sand packs contained within a 30 cm x?60 cm x?1.4 cm visual cell. Three of the experiments involved injection of a miscible, liquid solvent at the bottom of the sand pack, with subsequent upward displacement of the heavy oil; the fourth involved top-down injection of a gaseous solvent. The miscible liquid displacements were dominated by a single solvent finger, which broke through quickly to a producing well at the other end of the sand pack. Observed breakthrough times were consistent with a correlation that describes reported results at lower viscosity contrast. The gaseous solvent experiment exhibited fingering but also had features of a gravity-driven VAPEX process in its later stages. Numerical simulations using a commercial reservoir simulator have been successful in reproducing key features of the experiments. Realistic fingering patterns are produced in the simulations by assuming small, random spatial variations of permeability. The correct modelling of dispersion is crucial in matching the observed phenomena. For gaseous fingering and VAPEX processes, capillary effects are significant and should be included in simulations. Introduction Solvent-based processes for the recovery of heavy oil have attracted increasing attention in recent years. Much of this attention has focused on the Vapour Extraction or "VAPEX" process(1), a solvent analogue of steam assisted gravity drainage (SAGD). However, it has been suggested that for thin reservoirs, and particularly primary-depleted reservoirs, a cyclic solvent process might be preferred. Whereas VAPEX is analogous to SAGD, a cyclic solvent process would be analogous to the cyclic steam stimulation process. A concept for a cyclic process is shown in Figure 1. In this concept, solvent would be injected for a period of time, then oil produced from the same well; and this process would be repeated. A number of questions may be asked about the basic mechanisms of a cyclic solvent process and the resulting efficiency of oil recovery. The work reported here was aimed particularly at understanding the phenomenon of viscous fingering, which characterizes any such process in which a low viscosity solvent is injected into a high viscosity oil. Viscous fingering is an instability phenomenon which occurs when one fluid is displaced by another fluid of lower viscosity. The displacing fluid is said to "finger" into the resident fluid. The two fluids may be either miscible or immiscible, and the displacement may take place in a porous medium or even a Hele- Shaw cell(2, 3). </jats:sec