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Guest Editorial

J. Energy Resour. Technol. 2019;141(7):070301-070301-2. doi:10.1115/1.4043860.
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Special issue for the peer reviewed papers published from the 43rd International Clearwater Clean Energy Conference held during June 3–8, 2018 Clearwater, FL.

Commentary by Dr. Valentin Fuster

Special Section on 2018 Clean Energy

J. Energy Resour. Technol. 2019;141(7):070701-070701-8. doi:10.1115/1.4042822.

This study compares a staged thermal processing of the sewage sludge, with single step, integrated thermal processing. The aim of this study is to find the optimal conditions for drying and subsequently for carbonization/torrefaction of sewage sludge, regarding the energy consumption. This study presents the results of the drying tests performed at laboratory scale convective dryer for different parameters of drying agent (air). The tests were focused on finding and developing a method of drying that allows to minimize the energy consumption. Subsequently, both dry and vapothermal torrefaction was performed in the presence of oxygen. The kinetics of drying, using low quality heat as well as the properties of products and by-products of torrefaction in both regimes were determined. The process was characterized by mass yield and energy yield in both of the cases. There has been only scarce amount of literature studies published on the torrefaction of sewage sludge so far, without a detailed study of the composition of the torgas and tars of such origin. Performed study enables a comparison of two distinct scenarios of the processing, i.e., drying followed by dry torrefaction with a single stage of vapothermal torrefaction.

Topics: Sewage , Drying , Oxygen
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070702-070702-7. doi:10.1115/1.4042714.

Radial fractures are created in unconventional gas and oil reservoirs in modern well stimulation operations such as hydraulic refracturing (HRF), explosive fracturing (EF), and high energy gas fracturing (HEGF). This paper presents a mathematical model to describe fluid flow from reservoir through radial fractures to wellbore. The model can be applied to analyzing angles between radial fractures. Field case studies were carried out with the model using pressure transient data from three typical HRF wells in a lower-permeability reservoir. The studies show a good correlation between observed well performance and model-interpreted fracture angle. The well with the highest productivity improvement by the HRF corresponds to the interpreted perpendicular fractures, while the well with the lowest productivity improvement corresponds to the interpreted conditions where the second fracture is much shorter than the first one or where there created two merged/parallel fractures. Result of the case studies of a tight sand reservoir supports the analytical model.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070703-070703-12. doi:10.1115/1.4042915.

Ammonia (NH3) is an excellent hydrogen (H2) carrier that is easy to bulk manufacture, handle, transport, and use. NH3 is itself combustible and could potentially become a clean transport fuel for direct use in internal combustion engines (ICEs). This technical review examines the current state of knowledge of NH3 as a fuel in ICEs on its own or in mixtures with other fuels. A particular case of interest is to partially dissociate NH3 in situ to produce an NH3/H2 mixture before injection into the engine cylinders. A key element of the present innovation, the presence of H2 is expected to allow easy control and enhanced performance of NH3 combustion. The key thermochemical properties of NH3 are collected and compared to those of conventional and alternative fuels. The basic combustion characteristics and properties of NH3 and its mixtures with H2 are summarized, providing a theoretical basis for evaluating NH3 combustion in ICEs. The combustion chemistry and kinetics of NH3 combustion and mechanisms of NOx formation and destruction are also discussed. The potential applications of NH3 in conventional ICEs and advanced homogenous charge compression ignition (HCCI) engines are analyzed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070704-070704-7. doi:10.1115/1.4042747.

A prototype laser-induced breakdown spectroscopy (LIBS) sensor is tested for the determination of rare earth elements (Eu and Yb) in liquid and solid samples. The sensor head, built using a monolithic passively Q-switched (PQSW) Nd:YAG laser, produced a 1064 nm laser beam with ns pulses and an energy of 4.2 mJ. The measurements show good calibration linearity for both Eu and Yb with R2 values above 0.99 for all analyzed spectral lines in liquid and solid samples. Limits of detection (LODs) obtained were as low as 1 ppm, which are comparable to or better than those reported previously by using table top actively Q-switched systems. This study aims to develop a high sensitivity, field deployable sensor for characterizing existing and new sources of rare earth elements.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070705-070705-6. doi:10.1115/1.4042823.

In this study, the ignition and combustion behavior of raw and heat-treated single particles of lignite were experimentally investigated, with a focus on the effect of heat treatment temperatures. The lignite particles were heat treated to various final temperatures (473, 623 and 773 K) in nitrogen and characterized using proximate, ultimate, and Fourier transform infrared spectroscopy (FTIR) analysis. A single lignite particle of 2 or 3 mm in diameter was suspended on a silicon carbide fiber and burned in air in a horizontal tube furnace operating at 1123 K. The ignition and combustion process of the particle was record using a color CCD camera at 25 fps. The ignition mechanism, ignition delay time, volatile flame duration, and burnout time of the single particles were examined by processing the recorded images. The proximate and ultimate analysis results indicated that the volatile matter and oxygen contents decreased, while the carbon content increased with increasing temperature of heat treatment. This trend was consistent with observations in the FTIR analysis, in which the intensity of oxygen-containing functional groups decreased with increasing the heat treatment temperature. The ignition of raw and heat treated lignite particles followed a joint hetero-homogeneous mechanism under all conditions studied. The ignition delay time, volatile flame extinction time, and the total combustion time decreased with increasing heat treatment temperature up to 623 K. A further increase in the heat treatment temperature to 773 K resulted in prolonged key ignition and combustion characteristic times.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070706-070706-8. doi:10.1115/1.4043124.

Supercritical CO2 power cycles for fossil energy power generation will likely employ oxy-combustion at very high pressures, possibly exceeding 300 bar. At these high pressures, a direct fired oxy-combustor is more likely to behave like a rocket engine than any type of conventional gas turbine combustor. Issues such as injector design, wall heat transfer, and combustion dynamics may play a challenging role in combustor design. Computational fluid dynamics modeling will not only be useful, but may be a necessity in the combustor design process. To accurately model turbulent reacting flows, combustion submodels appropriate for the conditions of interest as defined by the turbulent time and length scales as well as chemical kinetic time scales are necessary. This paper presents a comparison of various turbulence–chemistry interaction (TCI) modeling approaches on a canonical, single injector, direct-fired sCO2 combustor. Large eddy simulation is used to model the turbulent combustion process with varying levels of injector oxygen concentration while comparing the effect of the combustion submodel on CO emissions and flame shape. While experimental data are not yet available to validate the simulations, the sensitivity of CO production and flame shape can be studied as a function of combustion modeling approach and oxygen concentration in an effort to better understand how to approach combustion modeling at these unique conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070707-070707-10. doi:10.1115/1.4043327.

Gas–solid fluidized bed reactors play an important role in many industrial applications. Nevertheless, there is a lack of knowledge of the processes occurring inside the bed, which impedes proper design and upscaling. In this work, numerical approaches in the Eulerian and the Lagrangian framework are compared and applied in order to investigate internal fluidized bed phenomena. The considered system uses steam/air/nitrogen as fluidization gas, entering the three-dimensional geometry through a Tuyere nozzle distributor, and calcium oxide/corundum/calcium carbonate as solid bed material. In the two-fluid model (TFM) and the multifluid model (MFM), both gas and powder are modeled as Eulerian phases. The size distribution of the particles is approximated by one or more granular phases with corresponding mean diameters and a sphericity factor accounting for their nonspherical shape. The solid–solid and fluid–solid interactions are considered by incorporating the kinetic theory of granular flow (KTGF) and a drag model, which is modified by the aforementioned sphericity factor. The dense discrete phase model (DDPM) can be interpreted as a hybrid model, where the interactions are also modeled using the KTGF; however, the particles are clustered to parcels and tracked in a Lagrangian way, resulting in a more accurate and computational affordable resolution of the size distribution. In the computational fluid dynamics–discrete element method (CFD–DEM) approach, particle collisions are calculated using the DEM. Thereby, more detailed interparticulate phenomena (e.g., cohesion) can be assessed. The three approaches (TFM, DDPM, CFD–DEM) are evaluated in terms of grid- and time-independency as well as computational demand. The TFM and CFD–DEM models show qualitative accordance and are therefore applied for further investigations. The MFM (as a variation of the TFM) is applied in order to simulate hydrodynamics and heat transfer to immersed objects in a small-scale experimental test rig because the MFM can handle the required small computational cells. Corundum is used as a nearly monodisperse powder, being more suitable for Eulerian models, and air is used as fluidization gas. Simulation results are compared to experimental data in order to validate the approach. The CFD–DEM model is applied in order to predict mixing behavior and cohesion effects of a polydisperse calcium carbonate powder in a larger scale energy storage reactor.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070708-070708-7. doi:10.1115/1.4043328.

With the supply restriction from traditional rare earth deposits, alternative sources of rare earth elements (REEs) such as coal are being studied. The United States National Energy Technology Laboratory has identified US coal deposits as a potential source of rare earth elements. Several techniques such as physical separation, flotation, ion-exchange, agglomeration, and leaching are being evaluated for the successful exploitation of these elements from coal and its by-products. A previous study published in the Geoscience BC 2018 mineral report on the characterization of REE in the British Columbian coal samples have shown that a major portion of the rare earth in the run of mine coal reports to the middling and tailing streams. Hence, this study is focused on the extraction of the rare earth from coal tailings. Several studies have shown the use of an alkali-acid leaching process to successfully demineralize various high ash coals to produce a clean coal concentrate since the ash-bearing components such as clay and quartz were removed from the coal during this process. In this study, the alkali-acid leach process was adopted to chemically clean coal tailings as well as to extract rare earth elements. Different process parameters such as sodium hydroxide (NaOH) concentration, temperature, and time were studied. Results showed that it is possible to extract more than 85% of REE with this process and simultaneously produce clean coal from coal tailing.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070709-070709-5. doi:10.1115/1.4043551.

This study was aimed to understand the rheological properties and stability characteristics of biochar-algae-water (BAW) slurry fuels prepared by wet milling. A pine sawdust biochar and a chlorella vulgaris algae were used in preparing the slurry fuels. The BAW slurries were formulated by mixing the biochar, algae, de-ionized water, lignosulfonic acid sodium salt, and then the mixture was ball-milled for various times. The BAW slurries with a constant solid loading of 45 wt % were prepared with varied algae proportion in algae/biochar mixture. The apparent viscosity and stability of BAW slurries were measured. It was found that D50 of the particles of the solid in the slurries decreased with increasing milling time. The viscosity of the slurries decreased first and then increased as milling time increased, reaching a minimal value when D50 of the solid was between 3 and 7 μm. The lowest viscosity of BAW slurries achieved at a given solid loading increased with increasing the algae proportion in the solid. The BAW slurries showed better stability at higher algae proportions due to enhanced flocculation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):070710-070710-6. doi:10.1115/1.4043629.

Thermochemical energy storage (TCES) represents one of the most promising energy storage technologies, currently investigated. It uses the heat of reaction of reversible reaction systems and stands out due to the high energy density of its storage materials combined with the possibility of long-term storage with little to no heat losses. Gas–solid reactions, in particular the reaction systems CaCO3/CaO, CaO/Ca(OH)2 and MgO/Mg(OH)2 are of key interest in current research. Until now, fixed bed reactors are the state of the art for TCES systems. However, fluidized bed reactors offer significant advantages for scale-up of the system: the improved heat and mass transfer allows for higher charging/discharging power, whereas the favorable, continuous operation mode enables a decoupling of storage power and capacity. Even though gas–solid fluidized beds are being deployed for wide range of industrial operations, the fluidization of cohesive materials, such as the aforementioned metal oxides/hydroxides, still represents a sparsely investigated field. The consequent lack of knowledge of physical, chemical, and technical parameters of the processes on hand is currently a hindering aspect for a proper design and scale-up of fluidized bed reactors for MW applications of TCES. Therefore, the experimental research at Technical University of Munich (TUM) focuses on a comprehensive approach to address this problem. Preliminary experimental work has been carried out on a fixed bed reactor to cover the topic of chemical cycle stability of storage materials. In order to investigate the fluidization behavior of the bulk material, a fluidized bed cold model containing a heat flux probe and operating at atmospheric conditions has been deployed. The experimental results have identified the heat input and output as the most influential aspect for both the operation and a possible scale-up of such a TCES system. The decisive parameter for the heat input and output is the heat transfer coefficient between immersed heat exchangers and the fluidized bed. This coefficient strongly depends on the quality of fluidization, which in turn is directly related to the geometry of the gas distributor plate. At TUM, a state-of-the-art pilot fluidized bed reactor is being commissioned to further investigate the aforementioned aspects. This reactor possesses an overall volume of 100 L with the expanded bed volume taking up 30 L. Two radiation furnaces (64 kW) are used to heat the reactor. The heat of reaction of the exothermal hydration reaction is removed by water, evaporating in a cooling coil, immersed in the fluidized bed. Fluidization is being achieved with a mixture of steam and nitrogen at operating temperatures of up to 700 °C and operating pressures between −1 and 6 bar(g). The particle size is in the range of d50 = 20 μm. While initial experiments on this reactor focus on optimal operating and material parameters, the long-term goal is to establish correlations for model design and scale-up purposes.

Commentary by Dr. Valentin Fuster

Review Article

J. Energy Resour. Technol. 2019;141(7):070801-070801-26. doi:10.1115/1.4041929.

Over the past few decades, due to the special features (i.e., easily produced, large-surface-area-to-volume ratio, and engineered particles with designed surface properties), nanoparticles have not only attracted great attentions from the oil and gas industry but also had various applications from drilling and completion, reservoir characterization, to enhanced oil recovery (EOR). As sensors or EOR agents, thus, fate and behavior of nanoparticles in porous media are essential and need to be investigated thoroughly. Nevertheless, most of the published review papers focus on particle transport in saturated porous media, and all of them are about steady-state flow conditions. So far, no attempts have been extended to systematically review current knowledge about nanoparticle transport in porous media with single-phase and two-phase flow systems under both steady-state and unsteady-state conditions. Accordingly, this review will discuss nanoparticle transport phenomena in porous media with its focus on the filtration mechanisms, the underlying interaction forces, and factors dominating nanoparticle transport behavior in porous media. Finally, mathematical models used to describe nanoparticle transport in porous media for both single-phase flow and two-phase flow under steady-state and transient flow conditions will be summarized, respectively.

Commentary by Dr. Valentin Fuster

Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2019;141(7):071201-071201-12. doi:10.1115/1.4042713.

Icing limits the performance of wind turbines in cold climates. The prediction of the aerodynamic performance losses and their distribution due to ice accretion is essential. Blade element momentum (BEM) is the basis of blade structural studies. The accuracy and limitations of this method in icing condition are assessed in the present study. To this purpose, a computational study on the aerodynamic performance of the full-scale NREL 5 MW rotor is performed. Three-dimensional (3D) steady Reynolds-averaged Navier–Stokes (RANS) simulations are performed for both clean and iced blade, as well as BEM calculations using two-dimensional (2D) computational fluid dynamics (CFD) sectional airfoil data. The total power calculated by the BEM method is in close agreement with the 3D CFD results for the clean blade. There is a 4% deviation, while it is underestimated by 28% for the iced one. The load distribution along the clean blade span differs between both methods. Load loss due to the ice, predicted by 3D CFD, is 32% in extracted power and the main loss occurs at the regions where the ice horn height exceeds 8% of the chord length.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2019;141(7):072001-072001-13. doi:10.1115/1.4042240.

The main objective of the current work is to investigate the thermodynamic performance of a novel solar powered multi-effect refrigeration system. The proposed cycle consists of a solar tower system with a heliostat field and central receiver (CR) that has molten salt as the heat transfer fluid, an absorption refrigeration cycle (ARC), an ejector refrigeration cycle (ERC), and a cascade refrigeration cycle (CRC). Energy and exergy analyses were carried out to measure the thermodynamic performance of the proposed cycle, using Dhahran weather data and operating conditions. The largest contribution to cycle irreversibility was found to be from the CR system (52.5%), followed by the heliostat field (25%). The first and second-law efficiencies improved due to the increase in the following parameters: ejector evaporator temperature, turbine inlet and exit pressures, and cascade evaporator temperature. Parametric analysis showed that the compressor delivery pressure, turbine inlet and exit pressures, hot molten salt outlet temperature, and ejector evaporator temperature significantly affect the refrigeration output.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072002-072002-13. doi:10.1115/1.4042239.

In air-conditioning, strategy of decoupling cooling and ventilation tasks has stimulated considerable interest in radiant cooling systems with dedicated outdoor air system (DOAS). In view of this, current paper presents a simulation study to describe energy saving potential of a solar, biogas, and electric heater powered hybrid vapor absorption chiller (VAC) based radiant cooling system with desiccant-coupled DOAS. A medium office building under warm and humid climatic condition is considered. To investigate the system under different operational strategies, energyplus simulations are done. In this study, a novel design involving solar collectors and biogas fired boiler is proposed for VAC and desiccant regeneration. Three systems are compared in terms of total electric energy consumption: conventional vapor compression chiller (VCC) based radiant cooling system with conventional VCC-DOAS, hybrid VAC-based radiant cooling system with conventional VCC-DOAS, and hybrid VAC-based radiant cooling system with desiccant-assisted VCC-DOAS. The hybrid VAC radiant cooling system and desiccant-assisted VCC-DOAS yields in 9.1% lesser energy consumption than that of the VAC radiant cooling system with conventional VCC-DOAS. Results also show that up to 13.2% energy savings can be ensured through triple-hybrid VAC radiant cooling system and desiccant-assisted VCC-DOAS as compared to that of the conventional VCC-based radiant system. The return on investment is observed to be 14.59 yr for the proposed system.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072003-072003-12. doi:10.1115/1.4042718.

This paper analyzes the performances and the emissions of the JETCAT P80 microengine, when jet A jet A +  10% biodiesel (BD), jet A + 20% biodiesel, and jet A + 30% biodiesel are utilized as fuel, and to each of these combinations is added 5% of Aeroshell Oil 500. The performances will be assessed based on the engine speed, for the generated thrust force, the temperature in front of the turbine, and on the fuel flow. The paper will investigate the performances and the emissions generated by the four fuel blends burning when the engine is idle, at the cruise and at the max regime. This will be realized by maintaining each of these regimes for approximately a minute and a half. During the tests, the vibrations were monitored both radially and axially for the observation of the engine function regimes. From the measurements, the concentrations of SO2, NOx, and CH4 will be analyzed, highlighting the emissions of SO2. There were performed measurements to determine the fuel blend's density in order to transform the values of the fuel flow from liter per hour into kilogram per second. Having these data registered from the engine, a jet engine cycle analysis at max regime will be performed based on the combustion efficiency, the thermal efficiency of the engine, and the specific fuel consumption.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2019;141(7):072901-072901-10. doi:10.1115/1.4042236.

Ultradeep fractured tight sandstone gas reservoir is easy to suffer from severe formation damage during the drill-in process, yet few papers have been published on the corresponding formation damage mechanisms. This paper focuses on a typical ultradeep fractured tight sandstone reservoir in the Tarim Basin, China. Fluid sensitivity damage, phase trapping damage, and the formation damage induced by oil-based drill-in fluids were evaluated by a serious of modified experimental methods. As a supplement, the rock physics and surface property were analyzed deeply. Results showed that severe fluid sensitivity damage occurred with a decrease in fluid salinity (critical value: 3/4 formation water salinity (FWS)) and an increase in fluid pH value (critical value: pH = 7.5). The change in water film thickness, the enhancement of hydrophilia, particle detachment, and dissolution of quartz/albite under high formation temperature are the main damage mechanisms. Abnormal low water saturation, mixed wettability, abundant clay minerals, and complex pore structures are contributing to the severe phase trapping damage. The dynamic damage rate of oil-based drill-in fluids is 60.01%, and inadequate loading capacity is the main trigger of lost circulation. Finally, a formation damage control strategy was proposed, and a field test proved its feasibility.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072902-072902-11. doi:10.1115/1.4042237.

It is quite common for oil/gas two-phase flow in developing fractured carbonate oil reservoirs. Many analytical models proposed for black oil wells in fractured carbonate reservoirs are limited to single-phase flow cases and conventional methods have been the use of numerical simulations for this problem. In this approach, a novel semi-analytical method is proposed to integrate the complexities of phase change, pressure-dependent pressure-volume-temperature (PVT) properties, two-phase flow behavior, and stress-dependent fracture permeability characteristics. A dual-porosity, black oil model considering the phase change and two-phase flow is applied to model the fractured carbonate reservoirs. To linearize the model, only flow equations of oil phase are used to develop the mathematical model. Nonlinear parameters and producing gas–oil ratio (GOR) are updated with coupled flowing material balance equations, followed by a novel proposed procedure for history matching of field production data and making forecasts. The semi-analytical method is validated with a commercial simulator Eclipse. The results show that both of the production rate curves of oil and gas phase using the proposed model coincide with the numerical simulator. The results also show that the effects of pressure-dependent fracture permeability, fracture porosity, and exterior boundary on production rate are significant. Stress sensitivity influences production rate during the whole process, reducing the cumulative production. Fracture porosity influences production rate during the intermediate flow periods. The exterior boundary affects production rate mainly in the early and intermediate production periods. Finally, a field example from the eastern Pre-Caspian basin is used to demonstrate the practicability of the method. Acceptable history match is achieved and the interpreted parameters are all reasonable.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072903-072903-7. doi:10.1115/1.4042281.

Drilling mud loss in highly porous media and fractured formations has been one of the industry's focuses in the past decades. Wellbore dynamics and lithology complexities continue to push for more research into accurate quantification and mitigation strategies for lost circulation and mud filtration. Conventional methods of characterizing mud loss with filtration data for field application can be time-consuming, particularly because of the interaction between several factors that impact mud loss and filtration. This paper presents a holistic engineering approach for characterizing lost circulation using pore-scale dynamic water-based mud (WBM) filtration data. The approaches used in this study include: factorial design of experiment (DoE), hypothesis testing, analysis of variance (ANOVA), and multiple regression analysis. The results show that an increase in temperature and rotary speed can increase dynamic mud filtration significantly. An increase in lost circulation material (LCM) concentration showed a significant decrease dynamic mud filtration. A combination of LCM concentration and rotary speed showed a significant decrease in dynamic mud filtration, while a combination of LCM concentration and temperature revealed a significant increase in dynamic mud filtration. Rotary speed and temperature combination showed an increase in dynamic mud filtration. The combined effect of these three factors was not significant in increasing or decreasing dynamic mud filtration. For the experimental conditions in this study, the regression analysis for one of the rocks showed that dynamic mud filtration can be predicted from changes in LCM concentration and rotary speed. The results and approach from this study can provide reliable information for drilling fluids design and selecting operating conditions for field application.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072904-072904-16. doi:10.1115/1.4042238.

In this study, a novel technique of low salinity hot water (LSHW) injection with addition of nanoparticles has been developed to examine the synergistic effects of thermal energy, low salinity water (LSW) flooding, and nanoparticles for enhancing heavy oil recovery, while optimizing the operating parameters for such a hybrid enhanced oil recovery (EOR) method. Experimentally, one-dimensional displacement experiments under different temperatures (17 °C, 45 °C, and 70 °C) and pressures (about 2000–4700 kPa) have been performed, while two types of nanoparticles (i.e., SiO2 and Al2O3) are, respectively, examined as the additive in the LSW. The performance of LSW injection with and without nanoparticles at various temperatures is evaluated, allowing optimization of the timing to initiate LSW injection. The corresponding initial oil saturation, production rate, water cut, ultimate oil recovery, and residual oil saturation profile after each flooding process are continuously monitored and measured under various operating conditions. Compared to conventional water injection, the LSW injection is found to effectively improve heavy oil recovery by 2.4–7.2% as an EOR technique in the presence of nanoparticles. Also, the addition of nanoparticles into the LSHW can promote synergistic effect of thermal energy, wettability alteration, and reduction of interfacial tension (IFT), which improves displacement efficiency and thus enhances oil recovery. It has been experimentally demonstrated that such LSHW injection with the addition of nanoparticles can be optimized to greatly improve oil recovery up to 40.2% in heavy oil reservoirs with low energy consumption. Theoretically, numerical simulation for the different flooding scenarios has been performed to capture the underlying recovery mechanisms by history matching the experimental measurements. It is observed from the tuned relative permeability curves that both LSW and the addition of nanoparticles in LSW are capable of altering the sand surface to more water wet, which confirms wettability alteration as an important EOR mechanism for the application of LSW and nanoparticles in heavy oil recovery in addition to IFT reduction.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072905-072905-13. doi:10.1115/1.4042230.

Produced water re-injection (PWRI) is an important economic and environmental-friendly option to convert waste to value with waterflooding operations. However, it often causes rapid injectivity decline. In the present study, a coreflood test on a low permeable core sample is carried out to investigate the injectivity decline behavior. An analytical model for well impedance (normalized reciprocal of injectivity) growth, along with probabilistic histograms of injectivity damage parameters, is applied to well injectivity decline prediction during produced water disposal in a thick low permeable formation (Völkersen field). An impedance curve with an unusual convex form is observed in both coreflood test and well behavior modeling; the impedance growth rate is lower during external filter cake build-up if compared with the deep bed filtration stage. Low reservoir rock permeability and, consequently, high values of filtration and formation damage coefficients lead to fast impedance growth during deep bed filtration; while external filter cake formation results in relatively slow impedance growth. A risk analysis employing probabilistic histograms of injectivity damage parameters is used to well behavior prediction under high uncertainty conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(7):072906-072906-15. doi:10.1115/1.4042413.

Reservoir characterization is a process to make dependable reservoir models using available reservoir information. There are promising ensemble-based methods such as ensemble Kalman filter (EnKF), ensemble smoother (ES), and ensemble smoother with multiple data assimilation (ES-MDA). ES-MDA is an iterative version of ES with inflated covariance matrix of measurement errors. It provides efficient and consistent global updates compared to EnKF and ES. Ensemble-based method might not work properly for channel reservoirs because its parameters are highly non-Gaussian. Thus, various parameterization methods are suggested in previous studies to handle nonlinear and non-Gaussian parameters. Discrete cosine transform (DCT) can figure out essential channel information, whereas level set method (LSM) has advantages on detailed channel border analysis in grid scale transforming parameters into Gaussianity. However, DCT and LSM have weaknesses when they are applied separately on channel reservoirs. Therefore, we propose a properly designed combination algorithm using DCT and LSM in ES-MDA. When DCT and LSM agree with each other on facies update results, a grid has relevant facies naturally. If not, facies is assigned depending on the average facies probability map from DCT and LSM. By doing so, they work in supplementary way preventing from wrong or biased decision on facies. Consequently, the proposed method presents not only stable channel properties such as connectivity and continuity but also similar pattern with the true. It also gives trustworthy future predictions of gas and water productions due to well-matched facies distribution according to the reference.

Commentary by Dr. Valentin Fuster

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