Radio-frequency Electromagnetic Heating Research Articles

Effect of native and injected nano-particles on the efficiency of heavy oil recovery by radio frequency electromagnetic heating

Previous attempts of EM heating have been made on the estimation of reservoir heating capabilities through numerical or analytical modeling. Experimental efforts, however, are needed, especially to test the oil property changes under EM radiation, temperature rise profile, and its effects on oil recovery. In this study, we introduced a conceptually scaled model (125×50×40cm) filled with sand to investigate the feasibility of EM heating for heavy oil recovery. For this purpose, a microwave antenna with a frequency of 2.45GHz and 2kW Magnetron based power generator was used to obtain the EM waves. Temperatures at different distances from the antenna were measured by fiber optic temperature sensors. Oil recovery experiments were conducted by placing the oil saturated sand samples in Buchner funnels at different distances from the antenna. The effect of temperature on viscosity of crude oil before and after exposure of EM radiation was also examined through the oil samples in Buchner funnels located in the model. The produced gases and oil collected were analyzed through GC to ensure the loss of component from the original oil and upgradation study. The experiments were repeated using Ni and Fe nanoparticles with oil and silica bead mixture, which can absorb EM waves. They improved the efficiency of the methods yielding a faster heating and thereby a quicker viscosity reduction. Finally, the experiments were repeated with high clay contents representing shale reservoirs. The recoveries and the change in oil properties were correlated to the power of the EM source and distance from this antenna. Temperature was raised by Ni nanoparticles (up to ~200°C) and therefore higher oil recovery (~30% of OOIP) was also obtained with Ni nanoparticles. Experimental observations and quantitative analyses could provide a vision for further development of EM heating as an alternative for situations where aqueous heating is not feasible.

Temperature responsive porous silicon nanoparticles for cancer therapy – spatiotemporal triggering through infrared and radiofrequency electromagnetic heating

One critical functionality of the carrier system utilized in targeted drug delivery is its ability to trigger the release of the therapeutic cargo once the carrier has reached its target. External triggering is an alluring approach as it can be applied in a precise spatiotemporal manner. In the present study, we achieved external triggering through the porous silicon (PSi) nanoparticles (NPs) by providing a pulse of infrared or radiofrequency radiation. The NPs were grafted with a temperature responsive polymer whose critical temperature was tailored to be slightly above 37°C. The polymer coating improved the biocompatibility of the NPs significantly in comparison with their uncoated counterparts. Radiation induced a rapid temperature rise, which resulted in the collapse of the polymer chains facilitating the cargo release. Both infrared and radiofrequency radiation were able to efficiently trigger the release of the encapsulated drug in vitro and induce significant cell death in comparison to the control groups. Radiofrequency radiation was found to be more efficient in vitro, and the treatment efficacy was verified in vivo in a lung carcinoma (3LL) mice model. After a single intratumoral administration of the carrier system combined with radiofrequency radiation, there was clear suppression of the growth of the carcinoma and a prolongation of the survival time of the animals. TOC imageThe temperature responsive (TR) polymer grafted on the surface of porous silicon nanoparticles (PSi NPs) changes its conformation in response to the heating induced by infrared or radiofrequency radiation. The conformation change allows the loaded doxorubicin to escape from the pores, achieving controlled drug release from TR PSi NPs, which displayed efficacy against malignant cells both in vitro and in vivo.

NUMERICAL MODELING OF HEAVY HYDROCARBON LIQUID HEATING

The results of two-dimensional mathematical modeling of heat and mass transfer in a highly viscous hydrocarbon liquid by inductive and radio-frequency (RF) electromagnetic (EM) heating are presented. The model takes into account the dependence of the liquid's viscosity and thermal conductivity on the temperature and also the presence of thermal convection effects. It is shown that the occurrence of volumetric heat sources inside the liquid caused by EM radiation yields an intensive deep heating as compared with inductive heating. Numerical calculations show that, in both these cases, the single vortex flow structure is formed in the whole volume of the liquid. However, RF EM heating provides a more homogeneous distribution of heat in the medium and requires three-fold less power consumption in comparison with induction heating.

Combining solvent injection, electromagnetic heating, and hydraulic fracturing for multistage heavy oil recovery

To model the combined multistage technologies of radio-frequency electromagnetic heating (RF-EM), solvent injection, and hydraulic fracturing, a mathematical model was developed. It was assumed that the well was previously hydraulically fractured and then the solvent was injected through it with simultaneous RF electromagnetic irradiation. The radiator of RF-EM waves was located at the bottom of the injection well. When the electromagnetic waves were irradiated into the reservoir, the temperature rises and the viscosity of the liquid decreases around the fractured well. While “cold” solvent was injected, it was heated at the bottom of the well so that the heat was transferred into the fracture and reservoir by convection. This leads to an increase of reservoir coverage by heating. The area of the thermal effect was determined by the length of fracture, duration of solvent injection, reduction in oil viscosity, increasing injectivity due to rising temperature, and solvent–heavy oil mixing around the bottomhole. Multistage process of reservoir stimulation was considered: (1) «Cold» production of heavy oil through the fractured well, (2) shut (shutdown) of the well without treatment, (3) solvent injection into the fractured production well with simultaneous RF-EM heating, (4) well was suspended to “soak” without any treatment, and (5) production of heavy oil with solvent without heating. The most efficient scenario was the combined RF-EM heating/fracturing multistage production technology. Recurring stages of solvent injection/RF-EM heating allowed maximum use of thermal energy and achieved the most efficient production growth.

Heavy Oil Production by Electromagnetic Heating in Hydraulically Fractured Wells

The results of numerical studies of heavy oil production by radio frequency–electromagnetic heating (RF–EM) from hydraulically fractured low-permeability reservoirs are presented. The fluid flow to a single vertical high-conductivity fracture is considered assuming that electrical and thermal properties of the reservoir rock and fluid-saturated fracture are the same. Comparative analysis is performed for the cases of heavy oil recovery by RF–EM radiation with hydraulic fracturing and “cold” production. Modeling of the combined multi-stage method and economic analysis for different RF–EM generator powers, differential pressure between the well and formation, and the fracture conductivity showed that the method is most effective for wells with “short” and low-conductivity hydraulic fractures.

Elastic constants of single crystalline β-Ti 70Nb 30

β-Ti70Nb30 (at.%) singles crystals were grown by a magnetic field controlled floating-zone technique with two-phase radiofrequency electromagnetic heating. The Young’s moduli of the crystals show pronounced anisotropy. The lowest value is E100 = 39.5 GPa. Comparison of the present results with recently published data and extrapolation to low Nb content of about 20 at.% shows that the preparation of β-Ti1−xNbx-based alloys with E100 ≈20–30 GPa should be possible, which would match the modulus of bone.

Effects of Electrical and Radio-Frequency Electromagnetic Heating on the Mass-Transfer Process during Miscible Injection for Heavy-Oil Recovery

This paper deals with the effect of radio-frequency electromagnetic (RF-EM) fields and electrical heating on the mass- and heat-transfer processes in a multi-component hydrocarbon system flowing in porous media. The more specific objective was to determine the major differences between the RF-EM effects and electric heating and eventually to propose the application conditions toward their field-scale applications. Critical parameters, including the viscosity reduction, that affect the recovery of heavy oil under the influence of these heating options with the emphasis on resolving the asphaltene precipitation problem were clarified. It was observed that the EM field influence on the residual oil recovery factor was more critical, and a greater recovery was obtained from the RF-EM case. This was attributed to the fact that the RF-EM field influences polar components of the oil, desorpting these components from the surface of the rock and adding to the production, as indicated by the scanning atomic force microscopy images. This critical role of the RF field on the adsorptive process during the displacement of high-viscosity oils eventually resulted in less asphaltene precipitation and pore plugging.

SAR versus Sinc: What is the appropriate RF exposure metric in the range 1–10 GHz? Part II: Using complex human body models

This is the second of the two articles that present modeling data and reasoned arguments for specifying the appropriate crossover frequency at which incident power flux density (S(inc)) replaces the peak 10 g averaged value of the specific energy absorption rate (SAR) as the designated basic restriction for protecting against radiofrequency electromagnetic heating effects in the 1-10 GHz range. In our first study, we compared the degree of correlation between these basic restrictions and the peak-induced tissue temperature rise (DeltaT) for a representative range of population/exposure scenarios using simple multi-planar models exposed to plane wave conditions. In this complementary study, complex heterogeneous head models for an adult and 12-year-old child were analyzed at 1, 3, 6, 8, and 10 GHz for a variety of exposure conditions. The complex models indicate that peak DeltaT is better correlated with peak 10 g SAR than S(inc) at 1 and 3 GHz and with S(inc) at 6-10 GHz, in contrast to the results from Part I. Considering the planar and complex body modeling results together, and given the equivocal indications of the two metrics in the 6-10 GHz range, we recommend that the breakpoint be set at 6 GHz. This choice is also based on other considerations such as ease of assessment. We also recommend that the limit level of S(inc) should be adjusted to provide a better match with 10 g SAR in the induced tissue temperature rise.

Convectional controlled crystal–melt interface using two-phase radio-frequency electromagnetic heating

The radio frequency floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid–liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure is created at a preferable phase shift of 90°. This change in the flow field has a significant influence on the shape of the solid–liquid interface. Due to their attractive properties for high temperature applications such as high melting temperature, low density, high modulus and good oxidation resistance, the magnetic system was applied to the crystal growth of TiAl alloys.

Localized current field hyperthermia: Effect on normal ocular tissue

Using a 500 kHz radiofrequency electromagnetic heating system, the effects of localized current field hyperthermia in normal rabbit eyes were examined. A specially designed scleral plaque placed on normal rabbit eyes was heated to temperatures of 43 degrees C, 45 degrees C, and 47 degrees C for a period of 45 min. The effects of hyperthermia were monitored by clinical examination, fluorescein angiography, electroretinography and histopathology. A graded effect with increasing temperature was found at the lower temperature, and it was confined to the treatment field. At 47 degrees C the electroretinogram was extinguished due to diffuse photoreceptor damage outside the treatment field, as demonstrated by histopathology and electron microscopy. This study indicates that hyperthermia at 45 degrees C for 45 min is the maximum allowable temperature without causing diffuse retinal damage in the normal rabbit eye.