Impact of Connate Brine Chemistry on In Situ Wettability and Oil Recovery: Pore-Scale Experimental Investigation

In this study, we present the results of micro- and macroscale core-flooding experiments performed on reservoir and outcrop sandstone core samples to investigate the impact of connate brine salinity on wettability and oil recovery. Numerous core samples were fully saturated with connate brines of varying salinities and then subjected to a dynamic wettability restoration (aging) process. The miniature core samples were imaged at high resolutions, and the images were used to measure in situ contact angles and evaluate the wettability alteration. Subsequently, some of the core samples were flooded with identical injection brine to examine the interrelationship between connate brine salinity and oil recovery potentials. The experimental observations demonstrate an ascending trend of initial oil–water contact angles with increases in brine salinity. We believe that brine film thickness, controlled by the DLVO interactions and initial cation-water bridging, is responsible for this wettability sensitivity. The equilibrium wettability state is found to shift toward reduced water-wetness when the connate brine salinity increases, which could be associated with improved oil−mineral bonding at higher salinities. Furthermore, using an ultralow salinity connate brine in the aging process results in a heterogeneous equilibrium wettability state including 46% of weakly water- and neutral-wet pores. It is believed that the ultralow salinity brine preserves stable brine films on some of the pore walls, prevents direct oil−mineral contact, and consequently reduces the degree of wettability alteration during the aging process. The subsequent waterflooding experiments on the aged samples indicated favorable oil recovery from media with heterogeneous equilibrium wettability compared to the weakly oil-wet samples. This was due to the existence of water- and neutral-wet pores that reduced the entry pressures of water-displacing-oil events and enhanced the accessibility of water to the oil-wet pore elements, which in turn improved the oil displacement efficiency

Fluorescent Ribonucleoside as a FRET Acceptor for Tryptophan in Native Proteins

A new fluorescent ribonucleoside analogue, containing 5-aminoquinazoline-2,4(1H,3H)-dione, acts as a Förster resonance energy transfer acceptor for tryptophan (R0 = 22 Å) and displays visible emission (440 nm). As tryptophan is frequently found at or near the recognition domains of RNA binding proteins, this FRET pair facilitates the study of RNA binding to native proteins and peptides, which is demonstrated here for the HIV-1 Rev association with the Rev Response Element (RRE)

FRET Enabled Real Time Detection of RNA-Small Molecule Binding

A robust analysis and discovery platform for antibiotics targeting the bacterial rRNA A-site has been developed by incorporating a new emissive U surrogate into the RNA and labeling the aminoglycosides with an appropriate fluorescence acceptor. Specifically, a 5-methoxyquinazoline-2,4(1H,3H)-dione-based emissive uracil analogue was identified to be an ideal donor for 7-diethylaminocoumarin-3-carboxylic acid. This donor/acceptor pair displays a critical Förster radius (R0) of 27 Å, a value suitable for an A-site-aminoglycoside assembly. Titrating the coumarin labeled aminoglycosides into the emissive A-site construct, labeled at position U1406, shows a decrease in donor emission (at 395 nm) and concurrent increase of the acceptor emission (at 473 nm). Titration curves, obtained by fitting the donor’s emission quenching or the augmentation of the acceptor’s sensitized emission, faithfully generate EC50 values. Titration of unlabeled ligands into the preformed FRET complex showed a continuous increase of the donor emission, with a concurrent decrease of the acceptor emission, yielding valuable data regarding competitive displacement of aminoglycosides by A-site binders. Detection of antibiotic binding is therefore not dependent on changes in the environment of a single fluorophore, but rather on the responsive interaction between two chromophores acting as a FRET pair, facilitating the determination of direct binding and competitive displacement events with FRET accuracy

Dynamic feature of average spreads, conditional variances and high state probabilities for AAA bonds.

<p>Dynamic feature of average spreads, conditional variances and high state probabilities for AAA bonds.</p

Dynamic feature of average spreads, conditional variances and high state probabilities for AA- bonds.

Dynamic feature of average spreads, conditional variances and high state probabilities for AA- bonds.</p

Summary statistics for macro-variables.

<p>Summary statistics for macro-variables.</p

Money supply (M1) from May 2013 to April 2017, which reflects the China's monthly currency growth year on year.

<p>Money supply (M1) from May 2013 to April 2017, which reflects the China's monthly currency growth year on year.</p

Dynamic feature of average spreads, conditional variances and high state probabilities for AA+ bonds.

<p>Dynamic feature of average spreads, conditional variances and high state probabilities for AA+ bonds.</p

Parameter estimation under fixed structure model.

<p>Parameter estimation under fixed structure model.</p

Summary statistics for average spreads of different credit grade.

<p>Summary statistics for average spreads of different credit grade.</p