Molecular Modes Elucidate the Nuclear Magnetic Resonance Relaxation of Viscous Fluids.

The Bloembergen, Purcell, and Pound (BPP) theory of nuclear magnetic resonance (NMR) relaxation in fluids dating back to 1948 continues to be the linchpin in interpreting NMR relaxation data in applications ranging from characterizing fluids in porous media to medical imaging (MRI). The BPP theory is founded on assuming molecules are hard spheres with H-H dipole pairs reorienting randomly; assumptions that are severe in light of modern understanding of liquids. Nevertheless, it is intriguing to this day that the BPP theory was consistent with the original experimental data for glycerol, a hydrogen-bonding molecular fluid for which the hard-sphere-rigid-dipole assumption is inapplicable.

Effects of velocity on N and CO foam flow with in-situ capillary pressure measurements in a high-permeability homogeneous sandpack.

The effects of velocity and gas type on foam flow through porous media have yet to be completely elucidated. Pressure drop and capillary pressure measurements were made at ambient conditions during a series of foam quality scan experiments in a homogenous sandpack while foam texture was simultaneously visualized. New insights into foam-flow behavior in porous media were discovered.

Effect of Nanoconfinement on NMR Relaxation of Heptane in Kerogen from Molecular Simulations and Measurements.

Kerogen-rich shale reservoirs will play a key role during the energy transition, yet the effects of nanoconfinement on the NMR relaxation of hydrocarbons in kerogen are poorly understood. We use atomistic MD simulations to investigate the effects of nanoconfinement on the H NMR relaxation times and of heptane in kerogen. In the case of , we discover the important role of confinement in reducing by ∼3 orders of magnitude from that of bulk heptane, in agreement with measurements of heptane dissolved in kerogen from the Kimmeridge Shale, without any models or free parameters.

Predicting H NMR relaxation in Gd-aqua using molecular dynamics simulations.

Atomistic molecular dynamics simulations are used to predict H NMR relaxation of water from paramagnetic Gd ions in solution at 25 °C. Simulations of the relaxivity dispersion function computed from the Gd-H dipole-dipole autocorrelation function agree within ≃8% of measurements in the range ≃ 5 ↔ 500 MHz, without any adjustable parameters in the interpretation of the simulations, and without any relaxation models. The simulation results are discussed in the context of the Solomon-Bloembergen-Morgan inner-sphere relaxation model, and the Hwang-Freed outer-sphere relaxation model.

NMR H-H Dipole Relaxation in Fluids: Relaxation of Individual H-H Pairs versus Relaxation of Molecular Modes.

The intramolecular H NMR dipole-dipole relaxation of molecular fluids has traditionally been interpreted within the Bloembergen-Purcell-Pound (BPP) theory of NMR intramolecular relaxation. The BPP theory draws upon Debye's theory for describing the rotational diffusion of the H-H pair and predicts a monoexponential decay of the H-H dipole-dipole autocorrelation function between distinct spin pairs. Using molecular dynamics (MD) simulations, we show that for both -heptane and water this is not the case.

Role of Wettability on the Adsorption of an Anionic Surfactant on Sandstone Cores.

We investigate the dynamic adsorption of anionic surfactant C alpha olefin sulfonate on Berea sandstone cores with different surface wettability and redox states under high temperature that represents reservoir conditions. Surfactant adsorption levels are determined by analyzing the effluent history data with a dynamic adsorption model assuming Langmuir isotherm. A variety of analyses, including surface chemistry, ionic composition, and chromatography, is performed.

A systematic approach to alkaline-surfactant-foam flooding of heavy oil: microfluidic assessment with a novel phase-behavior viscosity map.

The apparent viscosity of viscous heavy oil emulsions in water can be less than that of the bulk oil. Microfluidic flooding experiments were conducted to evaluate how alkali-surfactant-foam enhanced oil recovery (ASF EOR) of heavy oil is affected by emulsion formation. A novel phase-behavior viscosity map-a plot of added salinity vs.

Elucidating the H NMR Relaxation Mechanism in Polydisperse Polymers and Bitumen Using Measurements, MD Simulations, and Models.

The mechanism behind the H nuclear magnetic resonance (NMR) frequency dependence of and the viscosity dependence of for polydisperse polymers and bitumen remains elusive. We elucidate the matter through NMR relaxation measurements of polydisperse polymers over an extended range of frequencies ( = 0.01-400 MHz) and viscosities (η = 385-102 000 cP) using and in static fields, field-cycling relaxometry, and in the rotating frame.

Critical Role of Confinement in the NMR Surface Relaxation and Diffusion of -Heptane in a Polymer Matrix Revealed by MD Simulations.

The mechanism behind the NMR surface-relaxation times () and the large / ratio of light hydrocarbons confined in the nanopores of kerogen remains poorly understood and consequently has engendered much debate. Toward bringing a molecular-scale resolution to this problem, we present molecular dynamics (MD) simulations of H NMR relaxation and diffusion of -heptane in a polymer matrix. The high-viscosity polymer is a model for kerogen and bitumen that provides an organic "surface" for heptane.

Evaluating physicochemical properties of crude oil as indicators of low-salinity-induced wettability alteration in carbonate minerals.

The injection of low-salinity brine enhances oil recovery by altering the mineral wettability in carbonate reservoirs. However, the reported effectiveness of low-salinity water varies significantly in the literature, and the underlying mechanism of wettability alteration is controversial. In this work, we investigate the relationships between characteristics of crude oils and the oils' response to low-salinity water in a spontaneous imbibition test, aiming (1) to identify suitable indicators of the effectiveness of low-salinity water and (2) to evaluate possible mechanisms of low-salinity-induced wettability alteration, including rock/oil charge repulsion and microdispersion formation.

Effect of salinity, Mg and SO on "smart water"-induced carbonate wettability alteration in a model oil system.

Hypothesis: We present a systematic study of the "smart water" induced wettability alteration. This process is believed to be greatly affected by the brine salinity and the presence of Mg and SO in the brine.

Experiments And Modelling: To characterize the wettability alteration, we perform spontaneous imbibition measurement using Indiana limestone cores and a model oil with added naphthenic acid.

Polymer-Coated Nanoparticles for Reversible Emulsification and Recovery of Heavy Oil.

Heavy crude oil has poor solubility and a high density, making recovery and transport much more difficult and expensive than for light crude oil. Emulsifiers can be used to produce low viscosity oil-in-water emulsions for recovery and transport, but subsequent demulsification can be challenging. Here, we develop and implement interfacially active, pH-responsive polymer-coated nanoparticles (PNPs) to reversibly stabilize, recover, and break oil/water emulsions through variation of solution pH.

Viscoelastic diamine surfactant for stable carbon dioxide/water foams over a wide range in salinity and temperature.

Hypothesis: The viscosity and stability of CO/water foams at elevated temperature can be increased significantly with highly viscoelastic aqueous lamellae. The slow thinning of these viscoelastic lamellae leads to greater foam stability upon slowing down Ostwald ripening and coalescence. In the aqueous phase, the viscoelasticity may be increased by increasing the surfactant tail length to form more entangled micelles even at high temperatures and salinity.

Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications.

Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil.

Characterizing adsorption of associating surfactants on carbonates surfaces.

Hypothesis: The adsorption of anionic surfactants onto positively charged carbonate minerals is typically high due to electrostatic interactions. By blending anionic surfactants with cationic or zwitterionic surfactants, which naturally form surfactant complexes, surfactant adsorption is expected to be influenced by a competition between surfactant complexes and surfactant-surface interactions.

Experiments: The adsorption behavior of surfactant blends known to form complexes was investigated.

Destabilization, Propagation, and Generation of Surfactant-Stabilized Foam during Crude Oil Displacement in Heterogeneous Model Porous Media.

Foam flooding in porous media is of increasing interest due to its numerous applications such as enhanced oil recovery, aquifer remediation, and hydraulic fracturing. However, the mechanisms of oil-foam interactions have yet to be fully understood at the pore level. Here, we present three characteristic zones identified in experiments involving the displacement of crude oil from model porous media via surfactant-stabilized foam, and we describe a series of pore-level dynamics in these zones which were not observed in experiments involving paraffin oil.

Surface complexation modeling of calcite zeta potential measurements in brines with mixed potential determining ions (Ca, CO, Mg, SO) for characterizing carbonate wettability.

This study presents experiment and surface complexation modeling (SCM) of synthetic calcite zeta potential in brine with mixed potential determining ions (PDI) under various CO partial pressures. Such SCM, based on systematic zeta potential measurement in mixed brines (Mg, SO, Ca and CO), is currently not available in the literature and is expected to facilitate understanding of the role of electrostatic forces in calcite wettability alteration. We first use a double layer SCM to model experimental zeta potential measurements and then systematically analyze the contribution of charged surface species.

Modeling micelle formation and interfacial properties with iSAFT classical density functional theory.

Surfactants reduce the interfacial tension between phases, making them an important additive in a number of industrial and commercial applications from enhanced oil recovery to personal care products (e.g., shampoo and detergents).

Molecular dynamics simulations of NMR relaxation and diffusion of bulk hydrocarbons and water.

Molecular dynamics (MD) simulations are used to investigate H nuclear magnetic resonance (NMR) relaxation and diffusion of bulk n-CH to n-CH hydrocarbons and bulk water. The MD simulations of the H NMR relaxation times T in the fast motion regime where T=T agree with measured (de-oxygenated) T data at ambient conditions, without any adjustable parameters in the interpretation of the simulation data. Likewise, the translational diffusion D coefficients calculated using simulation configurations agree with measured diffusion data at ambient conditions.

Static Adsorption of an Ethoxylated Nonionic Surfactant on Carbonate Minerals.

The static adsorption of CE, which is a highly ethoxylated nonionic surfactant, was studied on different minerals using high-performance liquid chromatography (HPLC) combined with an evaporative light scattering detector (ELSD). Of particular interest is the surfactant adsorption in the presence of CO because it can be used for foam flooding in enhanced oil recovery applications. The effects of the mineral type, impurities, salinity, and temperature were investigated.

Role of Gas Type on Foam Transport in Porous Media.

We present the results of an experimental investigation of the effect of gas type and composition on foam transport in porous media. Steady-state foam strengths with respect to three cases of distinct gases and two cases containing binary mixtures of these gases were compared. The effects of gas solubility, the stability of lamellae, and the gas diffusion rate across the lamellae were examined.

Phase behavior and interfacial properties of a switchable ethoxylated amine surfactant at high temperature and effects on CO2-in-water foams.

The interfacial properties for surfactants at the supercritical CO2-water (C-W) interface at temperatures above 80°C have very rarely been reported given limitations in surfactant solubility and chemical stability. These limitations, along with the weak solvent strength of CO2, make it challenging to design surfactants that adsorb at the C-W interface, despite the interest in CO2-in-water (C/W) foams (also referred to as macroemulsions). Herein, we examine the thermodynamic, interfacial and rheological properties of the surfactant C12-14N(EO)2 in systems containing brine and/or supercritical CO2 at elevated temperatures and pressures.

Improved methylene blue two-phase titration method for determining cationic surfactant concentration in high-salinity brine.

The methylene blue (MB) two-phase titration method is a rapid and efficient method for determining the concentrations of anionic surfactants. The point at which the aqueous and chloroform phases appear equally blue is called Epton's end point. However, many inorganic anions, e.

Visualizing oil displacement with foam in a microfluidic device with permeability contrast.

Foam mobility control and novel oil displacement mechanisms were observed in a microfluidic device representing a porous media system with layered permeability. Foam was pre-generated using a flow-focusing microfluidic device and injected into an oil-wet, oil-saturated 2-D PDMS microfluidic device. The device is designed with a central fracture flanked by high-permeability and low-permeability zones stratified in the direction of injection.