Colloidally-induced fines release in porous media

A critical value of the total ionic strength (CTIS) has been found to exist for mixed salt solutions flowing in porous media. If the ionic strength drops below this value, significant amounts of fines are released in-situ due to colloidal forces, causing drastic formation damage. For a NaCl/CaCl2 system, the CTIS is strongly dependent on the relative amount of CaCl2 present in the solution. The concept of a critical salt concentration (CSC) and the analysis based on DLVO theory has been extended to mixed salt systems to estimate the CTIS. The difference between critical flocculation concentration (CFC), and the present definition of CTIS has been pointed out. Predictions of this analysis are consistent with experimental observations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28497/1/0000294.pd

Gravity-induced flocculation

In polydisperse colloidal systems, flocculation can occur as a result of the differential creaming rates between small and large particles. As an improvement on earlier work, we have rigorously modelled this process of gravity-induced flocculation by incorporating gravitational and interparticle (both attractive and repulsive) forces, as well as hydrodynamic interactions in our analysis. From this analysis capture cross-sections and collision frequencies can be precisely defined and computed. In the absence of electrostatic repulsion, the gravity-induced flocculation rate is approximately proportional to g0.80 (where g is the local acceleration of gravity) and not g as previously predicted. When electrostatic repulsion is significant, particles can flocculate into either a primary or secondary minimum (as described by DLVO theory), or remain dispersed. The possibility of two different types of doublets leads to an interesting phenomenon. When Brownian motion can be neglected, dilute spherical sols can be unstable at low and high gravitational forces, but stable against gravity-induced flocculation at intermediate values.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24704/1/0000125.pd

Beam spin asymmetry measurements of deeply virtual π0 production with CLAS12

The new experimental measurements of beam spin asymmetry were performed for the deeply virtual exclusive pi0 production in a wide kinematic region with the photon virtualities Q2 up to 6.6 GeV2 and the Bjorken scaling variable xB in the valence regime. The data were collected by the CEBAF Large Acceptance Spectrometer (CLAS12) at Jefferson Lab with longitudinally polarized 10.6 GeV electrons scattered on an unpolarized liquid-hydrogen target. Sizable asymmetry values indicate a substantial contribution from transverse virtual photon amplitudes to the polarized structure functions. The interpretation of these measurements in terms of the Generalized Parton Distributions (GPDs) demonstrates their sensitivity to the chiral-odd GPD ET, which contains information on quark transverse spin densities in unpolarized and polarized nucleons and provides access to the nucleon's transverse anomalous magnetic moment. Additionally, the data were compared to a theoretical model based on a Regge formalism that was extended to the high photon virtualities

Polysaccharides and bacterial plugging

Before any successful application of Microbial Enhanced Oil Recovery process can be realized, an understanding of the cells' transport and retentive mechanisms in porous media is needed. Cell transport differs from particle transport in their ability to produce polysaccharides, which are used by cells to adhere to surfaces. Cell injection experiments have been conducted using Leuconostoc cells to illustrate the importance of cellular polysaccharide production as a transport mechanism that hinders cell movement and plugs porous media. Kinetic studies of the Leuconostoc cells, carried out to further understand the plugging rates of porous media, have shown that the cells' growth rates are approximately equal when provided with monosaccharide (glucose and fructose) or sucrose. The only difference in cell metabolism is the production of dextran when sucrose is supplied as a carbon source. Experimentally it has also been shown that the cells' growth rate is weakly dependent upon the sucrose concentration in the media, and strongly dependent upon the concentration of yeast extract. The synthesis of cellular dextran has been found to lag behind cell generation, thus indicating that the cells need to reach maturity before they are capable of expressing the detransucrase enzyme and synthesizing insoluble dextran. Dextran yields were found to be dependent upon the sucrose concentration in the media. 10 refs., 9 figs., 9 tabs