Pore-scale simulation of low-salinity waterflooding in mixed-wet systems: effect of corner flow, surface heterogeneity and kinetics of wettability alteration.

The initial wettability state of the candidate oil reservoirs for low-salinity waterflooding (LSWF) is commonly characterized as mixed-wet. In mixed-wet systems, both the two-phase flow dynamics and the salt transport are significantly influenced by the corner flow of the wetting phase. Thus this study aims at comprehensive evaluation of LSWF efficiency by capturing the effect of corner flow and non-uniform wettability distribution. In this regard, direct numerical simulations under capillary-dominated flow regime were performed using the OpenFOAM Computational Fluid Dynamics toolbox. The results indicate that corner flow results in the transport of low-salinity water ahead of the primary fluid front and triggers a transition in the flow regime from a piston-like to multi-directional displacement. This then makes a substantial difference of 22% in the ultimate oil recovery factors between the 2D and quasi-3D models. Furthermore, the interplay of solute transport through corners and wettability alteration kinetics can lead to a new oil trapping mechanism, not reported in the literature, that diminishes LSWF efficiency. While the findings of this study elucidate that LSWF does exhibit improved oil recovery compared to high-salinity waterflooding, the complicating phenomena in mixed-wet systems can significantly affect the efficiency of this method and make it less successful.

Experimental Core Flooding Investigation of New ZnO-γAl2O3 Nanocomposites for Enhanced Oil Recovery in Carbonate Reservoirs.

Generally, crude oil production in mature oil reservoirs is difficult. In this regard, some nanoparticles have been used to upgrade injected water into oil reservoirs. These nanoparticles can be used in a variety of injectable waters, including smart water (SMW) with special salinity. This study aims to evaluate the performance of the injection of SMW with ZnO-γAl2O3 nanoparticles in enhanced oil recovery (EOR). The performance of SMW with ZnO-γAl2O3 nanoparticles in regard to contact angle (CA), interfacial tension (IFT) reduction, and oil production with core flooding tests was investigated. The newly prepared ZnO-γAl2O3 structure was characterized by energy dispersive X-ray (EDX), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses in this research. The effects of different concentrations of nanofluids on zeta potential (ZP) and conductivity were investigated. The ZP test confirmed the results of the stability tests of the developed nanofluids in water-based solutions. After the introduction of ZnO-γAl2O3 nanoparticles into the formation of brine and SMW solutions, oil-water (O/W) IFT was reduced. Based on the results, the IFT decreased more when nanoparticles and ions were present in the system. The results of the present study showed that at the concentration of SW+300 ppm ZnO-γAl2O3, the IFT value reached 11 mN/m from 27.24 mN/m. The results of the CA tests showed that improving the capabilities of salt water in the presence of nanoparticles has resulted in a very effective reduction. Also, in this regard, very hydrophilic wettability was achieved using SMW with stable nanoparticles. Moreover, the results of the present study showed that at the concentration of SMW+300 ppm ZnO-γAl2O3 nanoparticles, the CA value reached 31 from 161°. In the end, the solution of SW+300 ppm ZnO-γAl2O3 improved the OR by 15 and 24%. This research indicated that it is possible to develop and implement different nanoparticles by combining SMW to manage reservoir rock wettability and maximize OR from carbonate reservoirs. Thus, this combination as an effective agent could significantly increase reservoir sweep efficiency. Thus, as a result, using the established hybrid technique has distinct advantages over using SMW flooding alone.

Atomistic insight into salinity dependent preferential binding of polar aromatics to calcite/brine interface: implications to low salinity waterflooding.

This paper resolve the salinity-dependent interactions of polar components of crude oil at calcite-brine interface in atomic resolution. Molecular dynamics simulations carried out on the present study showed that ordered water monolayers develop immediate to a calcite substrate in contact with a saline solution. Carboxylic compounds, herein represented by benzoic acid (BA), penetrate into those hydration layers and directly linking to the calcite surface. Through a mechanism termed screening effect, development of hydrogen bonding between -COOH functional groups of BA and carbonate groups is inhibited by formation of a positively-charged Na+ layer over CaCO3 surface. Contrary to the common perception, a sodium-depleted solution potentially intensifies surface adsorption of polar hydrocarbons onto carbonate substrates; thus, shifting wetting characteristic to hydrophobic condition. In the context of enhanced oil recovery, an ion-engineered waterflooding would be more effective than injecting a solely diluted saltwater.

Ion-specific interactions at calcite-brine interfaces: a nano-scale study of the surface charge development and preferential binding of polar hydrocarbons.

This research provides an atomic-level insight into the synergic contribution of mono- and divalent ions to interfacial characteristics of calcite surfaces exposed to electrolyte solution containing organic compounds. The emphasis was placed on the ionic interactions responsible for charge developing mechanisms of calcite surfaces and also the capacity for adsorption of polar hydrocarbons, represented by benzoic acid (BA), at different brine compositions. For this purpose, molecular dynamics (MD) simulations were employed to explore the interplay of the main constituent ions of natural brines (Na+, Cl-, Mg2+, and SO42-) and BA at the interface of CaCO3. It was observed that surface accumulation of Na+ cations produces a positively charged layer immediate to the basal plane of calcite, validating the typical positive surface charge of carbonates reported by laboratory experiences. Meanwhile, a negatively charged layer appears beyond the sodium layer as a result of direct and solvent-mediated pairing of anions with Na+ cations lodged on the calcite substrate. In this process, sulfate adsorption severely diminishes surface charge to even a negative value in the case of a SO42--rich solution, providing an interpretation for the measurements reported in the literature. Our results revealed the inhibition of direct binding of BA molecules onto the calcite surface through complexation with protruding oxygen atoms of basal carbonates by the residing Na+ cations. Further, we noticed the sulfate-mediated pairing of BA molecules to the Na+ layer, which in effect intensifies surface adsorption of BA. However, BA-SO42- interaction is considerably reduced by magnesium cations shielding sulfate sites in the Mg2+-augmented brine. The findings presented in this study are of fundamental importance to advance our microscopic understanding of interfacial interactions in brine/oil/carbonate systems; with broad scientific and applied implications in the context of mobilizing organic contaminants trapped in aquifer sediments and enhancement of hydrophilicity of subsurface oil-bearing carbonate reservoirs by injecting ion-modified brine solutions.

A Deep Look into the Dynamics of Saltwater Imbibition in a Calcite Nanochannel: Temperature Impacts Capillarity Regimes.

This research concerns fundamentals of spontaneous transport of saltwater (1 mol·dm-3 NaCl solution) in nanopores of calcium carbonates. A fully atomistic model was adopted to scrutinize the temperature dependence of flow regimes during solution transport under CaCO3 nanoconfinement. The early time of capillary filling is inertia-dominated, and the solution penetrates with a near-planar meniscus at constant velocity. Following a transition period, the meniscus angle falls to a stabilized value, characterizing the capillary-viscous advancement in the calcite channel. At this stage, brine displacement follows a parabolic relationship consistent with the classical Lucas-Washburn (LW) theory. Approaching the slit outlet, the meniscus contact lines spread widely on the solid substrate and brine leaves the channel at a constant rate, in oppose to the LW law. The brine imbibition rate considerably increases at higher temperatures as a result of lower viscosity and greater tendency to form wetting layers on slit walls. We also pointed out a longer primary inertial regime and delayed onset of the viscous-capillary regime at higher temperatures. Throughout the whole span of capillary displacement, transport of sodium and chloride ions is tied to dynamics and diffusion of the water phase, even at the mineral interface. The results presented in this study are of broad implications in diverse science and technological applications.

How do ions contribute to brine-hydrophobic hydrocarbon Interfaces? An in silico study.

HYPOTHESIS: The saltwater-oil interface is of broad implication in geochemistry and petroleum disciplines. To date, the main focus has been on the surface contribution of polar, heavy compounds of crude oil, widely neglecting the role of non-polar hydrocarbons. However, non-polar compounds are expected to contribute to characteristics of oil-brine interfaces. METHODOLOGY: Utilizing molecular dynamics simulation, we aim to characterize ion behavior adjacent to hydrophobic organic phases. Concerning natural environments, NaCl, CaCl2 and Na2SO4 electrolytes at low (5 wt%) and high (15 wt%) concentrations were brought in contact with heptane and/or toluene which account for aliphatic and aromatic constituents of typical crude oils, respectively. The reproduced experimental data for interfacial tension, brines density and ions' diffusivities adequately verify our molecular calculations. FINDINGS: Ions accumulate nearby the intrinsically charge-neutral oil surfaces. A disparate surface-favoring propensity of ions causes the interfacial region to resemble an electrical layer and impose an effective surface charge onto the oil surface. Despite absence of any polar site, the effective surface charge density is hydrocarbon-dependent, with the highest and lowest values observed for toluene and heptane interfaces, respectively. Due to accumulation of toluene molecules nearby the brines, the interfacial characteristics of heptol (toluene-heptane mixture) is comparable to that of the toluene phase.

The Impact of Salinity on the Interfacial Structuring of an Aromatic Acid at the Calcite/Brine Interface: An Atomistic View on Low Salinity Effect.

This study aims to elucidate the impact of salinity on the interactions governing the adsorption of polar aromatic oil compounds onto calcite. To this end, molecular dynamics simulations were employed to assess adsorption of a model polar organic molecule (deprotonated benzoic acid, benzoate) on the calcite surface in NaCl brines of different concentration levels, namely, deionized water (DW), low-salinity water (LS, 5000 ppm), and sea water (SW; 45,000 ppm). Calcite was found to be completely covered by several well-ordered water layers. The top hydration layer is very compact and prevents direct adsorption of benzoates onto the substrate. Instead, Na+ ions form a distinct positively charged layer by adhering on the calcite substrate through inner-sphere complexion mode. Cl- ions mostly lodge on top of the adsorbed sodium cations, forming a negatively charged layer. The distribution of ions at the calcite/brine interface thus exhibits the features of an electrical double layer, composed of a Stern-like positive layer followed by a negative one. The positive charged layer attracts benzoates toward the surface. As such, the sodium ions attached onto the calcite can act as adsorption sites to connect benzoates to the surface. By increasing the salinity, more Na+ ions adsorb onto the calcite surface, and the density of benzoate molecules at the interface is enhanced as a result of more Na+ bridging ions. The monotonic salinity-dependent adsorption of benzoate molecules on calcite offers a mechanism driving additional oil recovery upon injection of diluted brine into subsurface carbonate reservoirs.

Genome annotation and comparative genomic analysis of Bacillus subtilis MJ01, a new bio-degradation strain isolated from oil-contaminated soil.

One of the main challenges in elimination of oil contamination from polluted environments is improvement of biodegradation by highly efficient microorganisms. Bacillus subtilis MJ01 has been evaluated as a new resource for producing biosurfactant compounds. This bacterium, which produces surfactin, is able to enhance bio-accessibility to oil hydrocarbons in contaminated soils. The genome of B. subtilis MJ01 was sequenced and assembled by PacBio RS sequencing technology. One big contig with a length of 4,108,293 bp without any gap was assembled. Genome annotation and prediction of gene showed that MJ01 genome is very similar to B. subtilis spizizenii TU-B-10 (95% similarity). The comparison and analysis of orthologous genes carried out between B. subtilis MJ01, reference strain B. subtilis subsp. subtilis str. 168, and close relative spizizenii TU-B-10 by microscope platform and various bioinformatics tools. More than 88% of 4269 predicted coding sequences in MJ01 had at least one similar sequence in genome of reference strain and spizizenii TU-B-10. Despite this high similarity, some differences were detected among encoding sequences of non-ribosome protein and bacteriocins in MJ01 and spizizenii TU-B-10. MJ01 has unique nucleotide sequences and a novel predicted lasso-peptide bacteriocin; it also has not any similar nucleotide sequence in non-redundant nucleotide data base.

Isolation and characterization of gram-positive biosurfactant-producing halothermophilic bacilli from Iranian petroleum reservoirs.

BACKGROUND: Petroleum reservoirs have long been known as the hosts of extremophilic microorganisms. Some of these microorganisms are known for their potential biotechnological applications, particularly production of extra and intracellular polymers and enzymes. OBJECTIVES: Here, 14 petroleum liquid samples from southern Iranian oil reservoirs were screened for presence of biosurfactant-producing halothermophiles. MATERIALS AND METHODS: Mixture of the reservoir fluid samples with a minimal growth medium was incubated under an N2 atmosphere in 40°C; 0.5 mL samples were transferred from the aqueous phase to agar plates after 72 hours of incubation; 100 mL cell cultures were prepared using the MSS-1 (mineral salt solution 1) liquid medium with 5% (w/v) NaCl. The time-course samples were analyzed by recording the absorbance at 600 nm using a spectrophotometer. Incubation was carried out in 40°C with mild shaking in aerobic conditions. Thermotolerance was evaluated by growing the isolates at 40, 50, 60 and 70°C with varying NaCl concentrations of 5% and 10% (w/v). Halotolerance was evaluated using NaCl concentrations of 5%, 10%, 12.5% and 15% (w/v) and incubating them at 40°C under aerobic and anaerobic conditions. Different phenotypic characteristics were evaluated, as outlined in Bergey's manual of determinative bacteriology. Comparing 16S rDNA sequences is one of the most powerful tools for classification of microorganisms. RESULTS: Among 34 isolates, 10 demonstrated biosurfactant production and growth at temperatures between 40°C and 70°C in saline media containing 5%-15% w/v NaCl. Using partial 16S rDNA sequencing (and amplified ribosomal DNA restriction analysis [ARDRA]) and biochemical tests (API tests 20E and 50 CHB), all the 10 isolates proved to be facultative anaerobic, Gram-positive moderate thermohalophiles of the genus Bacillus (B. thermoglucosidasius, B. thermodenitrificans, B. thermoleovorans, B. stearothermophilus and B. licheniformis), exhibiting surface-active behaviors. CONCLUSIONS: General patterns include decreasing the thermotolerance with increasing the salt concentrations and also more halotolerance in the aerobic environment compared with anaerobic conditions. The results demonstrated that Iranian petroleum reservoirs enjoy a source of indigenous extremophilic microorganisms with potential applications in microbial enhanced oil recovery and commercial enzyme production.

Modification of rock/fluid and fluid/fluid interfaces during MEOR processes, using two biosurfactant producing strains of Bacillus stearothermophilus SUCPM#14 and Enterobacter cloacae: a mechanistic study.

During any microbial enhanced oil recovery process, both cells and the metabolic products of bacteria govern the tertiary oil recovery efficiency. However, very accurate examination is needed to find the functionality of these tiny creatures at different reservoir conditions. In this regard, the effect of cell structure on ultimate microbial recovery efficiency which is the most dominant mechanism based on the microorganism types (gram-negative or gram-positive) was systematically investigated. At the first stage, possible different active mechanisms using Bacillus stearothermophilus SUCPM#14 strain were tested using specially designed injection protocol, in situ and ex situ core flooding experiments, interfacial tension, viscosity, pH and Amott wettability index measurements. At the second stage, comparing functionality of B. stearothermophilus SUCPM#14 (a gram-positive type) with the previously examined strain namely Enterobacter cloacae as a gram-negative type, proposed this hypothesis that the cell structure significantly affects the interfacial behaviors. New designed protocols were utilized to check the individual effects of cells, bioproducts and interaction of these together on the oil/water and also fluids/rock interfaces. The final results showed that the cells of B. stearothermophilus SUCPM#14 adhere more into the oil/water interface compared to E. cloacae and change its rheological properties; e.g. its elastic properties which affect the ultimate microbial oil recovery efficiency. Eventually, contradicting results revealed that biosurfactant produced by E. cloacae was able to considerably reduce the interfacial tension and alter the wettability of the rock (to neutral conditions) while biosurfactant produced by B. stearothermophilus SUCPM#14 was not very effective.

Core flooding tests to investigate the effects of IFT reduction and wettability alteration on oil recovery during MEOR process in an Iranian oil reservoir.

Microbial enhanced oil recovery (MEOR) refers to the process of using bacterial activities for more oil recovery from oil reservoirs mainly by interfacial tension reduction and wettability alteration mechanisms. Investigating the impact of these two mechanisms on enhanced oil recovery during MEOR process is the main objective of this work. Different analytical methods such as oil spreading and surface activity measurements were utilized to screen the biosurfactant-producing bacteria isolated from the brine of a specific oil reservoir located in the southwest of Iran. The isolates identified by 16S rDNA and biochemical analysis as Enterobacter cloacae (Persian Type Culture Collection (PTCC) 1798) and Enterobacter hormaechei (PTCC 1799) produce 1.53 g/l of biosurfactant. The produced biosurfactant caused substantial surface tension reduction of the growth medium and interfacial tension reduction between oil and brine to 31 and 3.2 mN/m from the original value of 72 and 29 mN/m, respectively. A novel set of core flooding tests, including in situ and ex situ scenarios, was designed to explore the potential of the isolated consortium as an agent for MEOR process. Besides, the individual effects of wettability alteration and IFT reduction on oil recovery efficiency by this process were investigated. The results show that the wettability alteration of the reservoir rock toward neutrally wet condition in the course of the adsorption of bacteria cells and biofilm formation are the dominant mechanisms on the improvement of oil recovery efficiency.

Enterobacter cloacae as biosurfactant producing bacterium: differentiating its effects on interfacial tension and wettability alteration Mechanisms for oil recovery during MEOR process.

Microbial enhanced oil recovery (MEOR) process utilizes microorganisms or their metabolites to mobilize the trapped oil in the oil formation after primary and secondary oil recovery stages. MEOR technique is considered as more environmentally friendly and low cost process. There are several identified mechanisms for more oil recovery using MEOR processes however; wettability alteration and interfacial tension (IFT) reduction are the important ones. Enterobacter Cloacae, a facultative bio-surfactant producer bacterium, was selected as a bacterial formulation due to its known performance on IFT reduction and wettability alteration. To quantify the effects of these two mechanisms, different tests including oil spreading, in situ and ex situ core flooding, wettability measurement (Amott), IFT, viscosity and pH measurements were performed. The obtained results revealed that the experimental procedure used in this study was able to quantitatively identify the individual effects of both mechanisms on the ultimate microbial oil recovery. The results demonstrated considerable effects of both mechanisms on the tertiary oil recovery; however after a proper shut in time period, more tertiary oil was recovered because of wettability alteration mechanism. Finally, SEM images taken from the treated cores showed biofilm formation on the rock pore surfaces, which is responsible for rock surface wettability alteration.

Investigating wettability alteration during MEOR process, a micro/macro scale analysis.

Wettability alteration is considered to be one of the important mechanisms that lead to increased oil recovery during microbial enhanced oil recovery (MEOR) processes. Changes in wettability will greatly influence the petrophysical properties of the reservoir rocks and determine the location, flow and distribution of different fluids inside the porous media. Understanding the active mechanisms of surface wettability changes by the bacteria would help to optimize the condition for more oil recovery. As the mechanisms behind wettability alteration are still poorly understood, the objective of this study is to investigate the wettability alteration at pore scale and find the most effective mechanism of wettability changes in different cases. The experiments were performed on different substrates at fresh condition or aged in crude oil to mimic various wetting conditions. Using an Enterobacter cloacae strain, the influence of bacterial metabolites, bacterial adhesion and bacterial solution with two different carbon sources on wettability were determined for different aging periods. Contact angle measurements were used to quantify the wettability alteration of the solid surfaces. Atomic force microscopy (AFM) experiments were also utilized to combine the macroscopic measurements of wettability with the microscopic study of the surface changes. It was found that the surface wettability could vary from neutral- or oil-wet to water-wet state. Bacterial adhesion and biofilm formation seems to be the dominant mechanism of wettability alteration. The aged glass surfaces regained their initial water wetness where the bacteria could remove the polar and asphaltene compounds from them.

Biosurfactant production under extreme environmental conditions by an efficient microbial consortium, ERCPPI-2.

The biosurfactant production potential of a new microbial consortium of Enterobacter cloacae and Pseudomonas sp. (ERCPPI-2) which was isolated from heavy crude oil-contaminated soil in the south of Iran, has been investigated under extreme environmental conditions. The isolated consortium produces a biosurfactant mixture with excessive oil spreading and emulsification properties. This consortium was able to grow and produce biosurfactant at temperatures up to 70 °C, pressures up to 6000 psia, salinities up to 15% (w/v), and in the pH range 4-10. Besides, the optimum biosurfactant production conditions were found to be 40 °C and 7.0 for the temperature and pH value, respectively. These conditions gave the best biosurfactant production of 1.74 g/1 when the cells were grown on a minimal salt medium containing 1.0% (w/v) olive oil, 1.0% (w/v) sodium nitrate supplemented with 1.39% (w/v) K(2)HPO(4) at 40 °C and 150 rpm after 48 h of incubation. The ERCPPI-2 could reduce surface and interfacial tensions to 31.7 and 0.65 mN/m from the original values of 58.3 and 16.9 mN/m, respectively. The isolated consortium produced biosurfactant using heavy crude oil as the sole source of carbon and emulsified the available heavy crude oil up to E(24)=83.4%. The results of the core holder flooding tests at simulated reservoir conditions demonstrated that the oil recovery efficiency due to the injection of the cell-free biosurfactant solution was 27.2%, and the bacterium injection reduced the final residual oil saturations to below 3% at optimum conditions.