Experimental Pore-Scale Study of a Novel Functionalized Iron-Carbon Nanohybrid for Enhanced Oil Recovery (EOR)

Nanofluid flooding, as a new technique to enhance oil recovery, has recently aroused much attention. The current study considers the performance of a novel iron-carbon nanohybrid to EOR. Carbon nanoparticles was synthesized via the hydrothermal method with citric acid and hybridize with iron (Fe3O4). The investigated nanohybrid is characterized by its rheological properties (viscosity), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analysis. The efficiency of the synthetized nanoparticle in displacing heavy oil is initially assessed using an oil–wet glass micromodel at ambient conditions. Nanofluid samples with various concentrations (0.05 wt % and 0.5 wt %) dispersed in a water base fluid with varied salinities were first prepared. The prepared nanofluids provide high stability with no additive such as polymer or surfactant. Before displacement experiments were run, to achieve a better understanding of fluid–fluid and grain–fluid interactions in porous media, a series of sub-pore scale tests—including interfacial tension (IFT), contact angle, and zeta potential—were conducted. Nanofluid flooding results show that the nanofluid with the medium base fluid salinity and highest nanoparticle concertation provides the highest oil recovery. However, it is observed that increasing the nanofluid concentration from 0.05% to 0.5% provided only three percent more oil. In contrast, the lowest oil recovery resulted from low salinity water flooding. It was also observed that the measured IFT value between nanofluids and crude oil is a function of nanofluid concentration and base fluid salinities, i.e., the IFT values decrease with the increase of nanofluid concentration and base fluid salinity reduction. However, the base fluid salinity enhancement leads to wettability alteration towards more water-wetness. The main mechanisms responsible for oil recovery enhancement during nanofluid flooding is mainly attributed to wettability alteration toward water-wetness and micro-dispersion formation. However, the interfacial tension (IFT) reduction using the iron-carbon nanohybrid is also observed but the reduction is not significant.

Experimental Study and History-Match of Near-Miscible WAG Coreflood Experiments on Mixed-Wet Carbonate Rocks

Water-alternating-gas (WAG) injection, both miscible and immiscible, is a widely used enhanced oil recovery method with over 80 field cases. Despite its prevalence, the numerical modeling of the physical processes involved remains poorly understood, and existing models often lack predictability. Part of the complexity stems from the component exchange between gas and oil and the hysteretic relative permeability effects. Thus, improving the reliability of numerical models requires the calibration of the equation of state (EOS) against phase behavior data from swelling/extraction and slim-tube tests, and the calibration of the three-phase relative permeability model against WAG coreflood experiments. This paper presents the results and interpretation of a complete set of two-phase and thee-phase displacement experiments on mixed-wet carbonate rocks. The three-phase WAG experiments were conducted on the same composite core at near-miscible reservoir condition; experiments differ in the injection order and length of their injection cycles. First, the two-phase water/oil and gas/oil displacement experiments and first cycles of WAG were used to estimate the two-phase relative permeabilities. Then, a synchronized history-matching procedure over the full set of WAG experiments and cycles was carried out to tune Larsen ans Skauge WAG hysteresis model—namely the Land gas traping parameter, the gas reduction exponent, the residual oil reduction factor and three-phase water relative permeability. The second part of this paper deals with the multiphase upscaling of microscopic displacement properties from plug to coarse grid reservoir scale. The two-phase relative permeability curves and three-phase WAG parameters were upscaled using a sector model to preserve the displacement process and reservoir performance. The result of the coreflood calibration indicate that the two-phase displacement and first cycles of WAG yield a consistent set of two-phase relative permeabilities. Including the full set of WAG experiments allowed a robust calibration of the hysteresis model.

An Experimental Investigation of Mass Transfer in Tight Dual-Porosity Systems

During gas injection in ultra-tight fractured reservoirs, molecular diffusion can play a dominant role in the mass transfer process and enhance recovery by extracting oil components from matrix and delaying gas breakthrough. There has been a growing interest from scholars and operators to study the effect of diffusive mass transfer on the potential incremental recovery from CO2 and rich gas injection. However, many fundamental questions pertaining to the physics of multicomponent multiphase flow and transport are still left unanswered. This paper aims to improve the understanding of multicomponent diffusive mass transfer between matrix and fracture blocks through experimental and modeling work. Displacement experiments were carried out using analog fluids and mesoporous medium to effectively isolate and study the relevant physical mechanisms at play. The experiments were performed in packed columns utilizing silica-gel particles that have internal porosity. The particle size is 40-70 micron with highly controlled internal pore size of 6 nm that makes up approximately 50% of the overall porosity. The quaternary analog fluids system consists of Water, Methanol, Isopropanol, and Isooctane, was used because it mimics the phase behavior of CO2, Methane, Butane and Dodecane mixtures at 2,280 psi and 100°C. Our selection of the analog fluid system and porous medium allowed us to investigate matrix-fracture fluid exchange as observed during an enhanced recovery operation in an ultra-tight fractured system. The effluents from these displacement experiments served as the basis for our analysis of diffusive mass transfer. The role of molecular diffusion in the displacement experiments was investigated by first performing separate diffusion experiments to obtain diffusion coefficients for all relevant binary mixtures. Infinite dilution diffusion coefficients were measured for all binary mixtures and then used to model binary and multicomponent diffusion coefficients over the whole composition range. The accuracy of this approach was determined by performing additional binary diffusion experiments over a broader range of compositions. The displacement experiments were simulated using an in-house simulator and excellent agreement was obtained: The extensive experimental/modeling work related to the diffusion coefficients of the analog fluid system was used in interpreting the diffusive mass transfer between the matrix (stagnant) and fracture (flowing) domains via a 1D linear model. The presented work provides new insights into the role of diffusive mass transfer in ultra-tight fractured systems and builds a framework to highlight the critical data needed to effectively characterize and simulate recovery from such complex geological settings.

Environmental Reconstruction and Tracking as Methods to Explore Social Interactions in Marine Environments: A Test Case With the Mediterranean Rainbow Wrasse Coris julis

A key aspect of understanding social interactions in marine animals is determining whether individuals freely interact in fission-fusion groups, or have spatially structured interactions, for example territories or home ranges. Territoriality can influence access to mates, food resources, or shelter sites, and may also impact conservation efforts, as the delineation of marine protected areas relies on knowledge of home ranges and movement patterns. However, accurately determining distribution and movement is challenging for many marine species, especially small and medium species, which cannot carry beacons or tags to automatically measure movement, and are also difficult for human observers to accurately follow. Yet these smaller species comprise the bulk of near-shore assemblages, and are essential conservation targets. As such, novel solutions for monitoring movement and behavior are required. Here we use a combination of tracking and environmental reconstruction to explore territoriality, aggression, and navigation in a small marine fish, explicitly applying this technique to questions of sociality in the marine environment. We use the Mediterranean Rainbow Wrasse, Coris julis, as a test case, but this approach can be extended to many other species and contexts. In contrast with previous reports for this species, we find that during our observation period, female C. julis occupy consistent territories over sand patches, and that they defend these territories against same-sex conspecifics. Displacement experiments revealed two further important social behavioral traits – first that displaced individuals were able to navigate back to their territory, avoiding almost all other female territories as they returned. Second that when displaced fish approached the territories of others, residents of these territories were often aggressive to the non-neighboring fish, in contrast with our observations of low aggression counts toward their natural neighbors. Resident fish therefore appear to show differing levels of aggressiveness depending on their social relationship with same-sex conspecifics. Overall, these results suggest a sophisticated degree of social behavior in this marine wrasse, dependent on social and structural environment, but which can only effectively be revealed by state-of-the-art tracking and environment reconstruction techniques.

Short-range homing in camels: displacement experiments

Camels (Camelus dromedarius) are known to have good navigational abilities and can find their home after displacement to far places; however, there are no studies available on the navigational strategies employed by the camels in homing behavior. Thus, the aim of this study was to investigate the strategies by displacing female camels equipped with GPS trackers 6 km away from home to totally unfamiliar locations. The experiments comprised displacing nursing or non-nursing female camels 6 km from their living pens to an unfamiliar release site. Some camels were taken to the release site on foot, others were hauled on a truck, both during daytime and night-time. Displacements were either straight to the release points, or they consisted in convoluted paths. As a result, the camels were able to return home efficiently and rather directly after straight outward journeys but failed to do so after having performed convoluted trips to the release point. Moreover, impairing olfactory, visual, and auditory inputs by using mouth/nose muzzles eye covers and headphones did not affect homing ability. Based on these experiments the most likely hypothesis is that during their small-scale round trips the camels relied on path integration, and that this strategy is disrupted when the camels were subjected to disorientation procedures before release.

Pore-Scale Investigation of Microscopic Remaining Oil Variation Characteristic in Different Flow Rates Using Micro-CT

The main means of secondary oil recovery is water flooding, which has been widely used in various oilfields. Different flow rates have a great impact on the recovery ratio and the occurrence of remaining oil. Scholars have carried out extensive research on it, but mostly on the macro scale, and research on the three-dimensional micro scale is also limited by accuracy and a lack of accurate understanding. In this paper, micro-CT and core displacement experiments are used to intuitively show the occurrence state of remaining oil under different flow rates. Through a series of quantitative image processing methods and remaining oil classification methods, the occurrence characteristics of remaining oil under different flow rates are systematically evaluated and studied. The results show that: (1) As the displacement rate increases, the remaining oil saturation decreases (61%; 35%; 23%), but the remaining oil is more evenly distributed along the slice; (2) Two lower displacement speeds (0.003 mL/min; 0.03 mL/min) can reduce the volume of huge oil clusters under oil-saturated conditions, and the highest displacement speed (0.3 mL/min) can completely break up large oil clusters into small oil droplets. At the same time, the shape factor of the oil clusters also gradually increases; (3) The proportion of continuous remaining oil volume decreases, and the proportion of discontinuous remaining oil increases. Discontinuous remaining oil is the main production target of EOR; (4) After water flooding, the microscopic remaining oil is more inclined to the middle and corner parts of the larger pores.

Temperature-resistant and salt-tolerant mixed surfactant system for EOR in the Tahe Oilfield

A new temperature-resistant and salt-tolerant mixed surfactant system (referred to as the SS system) for enhancing oil recovery at the Tahe Oilfield (Xinjiang, China) was evaluated. Based on the analysis of the crude oil, the formation water and rock components in the Tahe Oilfield, the long-term thermal stability, salt tolerance and the ability to change the wettability, interfacial activity and oil washing efficiency of the mixed surfactant system were studied. The system contains the anionic surfactant SDB and another cationic surfactant SDY. When the total mass concentration of the SS solution is 0.15 wt%, m(SDB)/m(SDY) ratio is 1 to 1, and excellent efficiencies are achieved for oil washing for five kinds of Tahe Oilfield crude oils (more than 60%). In addition, after adding cationic surfactant, the adsorption capacity of the surfactant is further reduced, reaching 0.261 mg/g. The oil displacement experiments indicate that under a temperature of 150 °C and a salinity of 24.6 × 104 mg/L, the SS system enhances the oil recovery by over 10% after water flooding. The SS anionic–cationic surfactant system is first presented in the open literature that can be successfully applied to obtain predictions of Tahe Oilfield carbonate reservoirs with a high temperature and high salinity.

Study on Competitive Adsorption and Displacing Properties of CO2 Enhanced Shale Gas Recovery: Advances and Challenges

CO2 enhanced shale gas recovery (CO2-ESGR) draws worldwide attentions in recent years with having significant environmental benefit of CO2 geological storage and economic benefit of shale gas production. This paper is aimed at reviewing the state of experiment and model studies on gas adsorption, competitive adsorption of CO2/CH4, and displacement of CO2-CH4 in shale in the process of CO2-ESGR and pointing out the related challenges and opportunities. Gas adsorption mechanism in shale, influencing factors (organic matter content, kerogen type, thermal maturity, inorganic compositions, moisture, and micro/nano-scale pore), and adsorption models are described in this work. The competitive adsorption mechanisms are qualitatively ascertained by analysis of unique molecular and supercritical properties of CO2 and the interaction of CO2 with shale matrix. Shale matrix shows a stronger affinity with CO2, and thus, adsorption capacity of CO2 is larger than that of CH4 even with the coexistence of CO2-CH4 mixture. Displacement experiments of CO2-CH4 in shale proved that shale gas recovery is enhanced by the competitive adsorption of CO2 to CH4. Although the competitive adsorption mechanism is preliminary revealed, some challenges still exist. Competitive adsorption behavior is not fully understood in the coexistence of CO2 and CH4 components, and more experiment and model studies on adsorption of CO2-CH4 mixtures need to be conducted under field conditions. Coupling of competitive adsorption with displacing flow is key factor for CO2-ESGR but not comprehensively studied. More displacement experiments of CO2-CH4 in shale are required for revealing the mechanism of flow and transport of gas in CO2-ESGR.