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Research Papers: Air Emissions From Fossil Fuel Combustion

J. Energy Resour. Technol. 2013;136(2):021101-021101-6. doi:10.1115/1.4025286.

As petroleum resources are finite, it is imperative to use them wisely in energy conversion applications and, at the same time, develop alternative energy sources. Biomass is one of the renewable energy sources that can be used to partially replace fossil fuels. Biomass-based fuels can be produced domestically and can reduce dependency on fuel imports. Due to their abundant supply, and given that to an appreciable extent they can be considered carbon-neutral, their use for power generation is of technological interest. However, whereas biomasses can be directly burned in furnaces, such a conventional direct combustion technique is ill-controlled and typically produces considerable amounts of health-hazardous airborne compounds. Thus, an alternative technology for biomass utilization is described herein to address increasing energy needs in an environmentally-benign manner. More specifically, a multistep process/device is presented to accept granulated or pelletized biomass, and generate an easily-identifiable form of energy as a final product. To achieve low emissions of products of incomplete combustion, the biomass is gasified pyrolytically, mixed with air, ignited and, finally, burned in nominally premixed low-emission flames. Combustion is thus indirect, since the biomass is not directly burned, instead its gaseous pyrolyzates are burned upon mixing with air. Thereby, combustion is well-controlled and can be complete. A demonstration device has been constructed to convert the internal energy of biomass into “clean” thermal energy and, eventually to electricity.

Topics: Biomass , Pyrolysis
Commentary by Dr. Valentin Fuster

Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2013;136(2):021201-021201-8. doi:10.1115/1.4025408.

Three individual wave power generation technologies were studied and evaluated using multicriteria decision analysis through the use of the PROMETHEE method. To evaluate the three technologies, data were collected from previously performed experimental testing on the performance of each wave power generation technology. These data were used to feed into seven different criteria; namely the capacity factor, rated power, capital cost, operation and maintenance (O&M) costs, cost of electricity (COE) for a 10 year payback, maturity, and survivability. The associated data and criteria were used to determine the optimal technology. The results from the Decision Lab modeling ranked the Wave Dragon, AquaBuOY, and Pelamis technologies as 1, 2, and 3, respectively, for all three locations: Tofino/Ucluelet, Hibernia Oil Platform, and St. John's, Newfoundland. A sensitivity analysis of the threshold values determined for the baseline modeling indicated that the original ranking was essentially unaffected when the threshold values were modified (increased and decreased). The weights of the criterion were individually adjusted to evaluate any change in ranking order. A sizable increase in weighting of greater than 40% of any one criterion (while the others were weighed equally) resulted in a change of the overall ranking order of the three technologies. Final weightings on each of the criterion were assigned with preference on rated power, COE, and maturity stage. All other criteria were weighted equally and like the baseline modeling output, the results of the model ranked Wave Dragon, AquaBuOY, and Pelamis from most favorable to least favorable for all three of the locations analyzed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;136(2):021202-021202-7. doi:10.1115/1.4025409.

A wind tower system having a three dimensional heliacal wind deflecting structure is studies in this work. The purpose of the helical structure is to increase the natural wind speed and direct the follow of the wind toward two columns of horizontal-axis rooftop-size wind turbines that are installed in the grooves of the helical structure, diametrically opposed to each other. Computational fluid dynamics analyses were conducted to determine the influence of the helical structure on the wind speed reaching the turbines. A wind speed amplification coefficient was determined for a helical structure of 6.7 m outer diameter. The velocity profiles of the wind flow around the helical structure were determined under a postulated wind speed of 4.47 m/s. The flow was modeled as turbulent with a Reynolds Number of 2,052,167. Standard “k–ε” turbulent model with “near wall treatment” and “standard wall function” were adapted in all analysis. A “y+” value of 50 was held constant in all simulation. The grid-size effects on the accuracy of the results were examined. Convergence criterion was satisfied in each case. This study shows that the helical structure having an outer diameter of 6.7 m results in an average wind speed increase factor of 1.52. An experimental wind tower system was fabricated and installed at an elevation of 40 m above the ground. The wind tower system comprised of four identical rooftop size wind turbines, each having 1.6 KW name-plate-rating. A helical wind deflecting structure of 11 m tall, and 7 m in major diameter was used in fabrication of the tower. An active yaw-control mechanism was used to orient the tower into the prevailing wind. The experimental results show that as the result of the use of the wind deflecting structure, an average power amplification factor of 4.69 was obtained for the tower, in comparison with the standard standalone installation of the four wind turbines.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021203-021203-5. doi:10.1115/1.4026200.

Vast ocean areas of planet Earth are exposed year-round to strong wind currents. We suggest that this untapped ocean wind power be exploited by the use of sailing ships. The availability of constantly updated meteorological information makes it possible to operate the ships in ocean areas with optimum wind power so that the propulsive ship power can be converted into electric power by means of ship-mounted hydro-power generators. Their electric power output then is fed into ship-mounted electrolyzers to convert sea water into hydrogen and oxygen. In this paper, we estimate the ship size, sail area, and generator size to produce a 1.5 MW electrical power output. We describe a new oscillating-wing hydro-power generator and present results of model tests obtained in a towing tank. Navier-Stokes computations are presented to provide an estimate of the power extraction efficiency and drag coefficient of such a generator which depends on a range of parameters such as foil maximum pitch angles, plunge amplitude, phase between pitch and plunge and load. Also, we present a discussion of the feasibility of sea water electrolysis and of the reconversion of hydrogen and oxygen into electricity by means of shore-based hydrogen-oxygen power plants.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021204-021204-10. doi:10.1115/1.4026202.

A simple cooling cogeneration has been developed by coupling a Kalina cycle system (KCS) with a vapor absorption refrigeration (VAR) system. The working fluid used in this theoretical thermodynamic evaluation is ammonia water mixture. A low temperature heat recovery (150 °C–200 °C) from engine exhaust gas, solar collectors, or similar can be used to operate the plant. A controlling facility is provided to set the required amount of power or cooling to meet the variable demand. In this proposed plant, the liquid refrigerant absorbs more amount of heat from evaporator surroundings with a flow control located in between power and cooling cycles. The extra included components are condenser, heat exchanger and throttling device over KCS plant. Due to possibility of more cooling, it offers high energy utilization factor (EUF). The coupled plant characteristics are studied with changes in mass split ratio, separator vapor fraction, separator temperature, and turbine concentration to develop efficient working conditions. The power mass split ratio is varied from 80% to 100% to run the coupled plant at nearly full load conditions. The separator vapor fraction and temperature are optimized at 45% and 150 °C, respectively. It is recommended to maintain the turbine concentration above 0.85 for optimum power and cooling. The maximum cycle EUF and plant EUF are 0.15 and 0.06, respectively, at 80% power mass split ratio. The specific power and specific cooling at these conditions are 62 kW/kg and 72 kW/kg, respectively.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021205-021205-9. doi:10.1115/1.4026635.

Wave-driven reverse osmosis desalination systems can be a cost-effective option for providing a safe and reliable source of drinking water for large coastal communities. Such systems usually require the stabilization of pulsating pressures for desalination purposes. The key challenge is to convert a fluctuating pressure flow into a constant pressure flow. To address this task, stub-filters, accumulators, and radially elastic-pipes are considered for smoothing the pressure fluctuations in the flow. An analytical model for fluidic capacitance of accumulators and elastic pipes are derived and verified. Commercially available accumulators in combination with essentially rigid (and low cost) piping are found to be a cost-effective solution for this application, and a model for selecting accumulators with the required fluidic-capacitance for the intended system is thus presented.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021206-021206-9. doi:10.1115/1.4026914.

In an attempt to improve the fuel economy and reduce the exhaust emissions of motorcycles, some manufactures have developed commercialized motorcycles equipped with automatic idling-stop and go (AISG) functionality. Even though research efforts devoted to the idling-stop strategy have demonstrated its effectiveness, motorcycles equipped with the AISG device are not popular because the general public still has some concerns about them. This paper aims to evaluate the benefits and feasibility of a commercialized motorcycle with AISG functionality with regard to the public's concerns about fuel economy and emission problems during engine restart transients. In order to verify the accuracy of the analytical results and control for variable driver characteristics, a motorcycle chassis dynamometer was used to recreate the urban driving pattern. Furthermore, the feasibility of fuel-saving and emissions improvement by adjusting fuel-injection signal of the engine control unit (ECU) during engine restart operation was also evaluated. The experimental results showed that the addition of the fuel-injection modulation plus idling-stop strategy can improve the fuel economy rate by up to 12.2% and reduce carbon monoxide (CO) emission by up to 36.95% in comparison with the non-idling stop case.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021207-021207-8. doi:10.1115/1.4027409.

This paper presents, assesses, and optimizes a point absorber wave energy converter (WEC) through numerical modeling, simulation, and analysis. Wave energy conversion is a technology uniquely suited for assisting in power generation in the offshore oil and gas platforms. A linear frequency domain model is created to predict the behavior of the heaving point absorber WEC system. The hydrodynamic parameters are obtained with AQWA, a software package based on boundary element methods. A linear external damping coefficient is applied to enable power absorption and an external spring force is introduced to tune the point absorber to the incoming wave conditions. The external damping coefficient and external spring forces are the control parameters, which need to be optimized to maximize the power absorption. Two buoy shapes are tested and a variety of diameters and drafts are compared. Optimal shape, draft, and diameter of the model are then determined to maximize its power absorption capacity.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Conversion/Systems

J. Energy Resour. Technol. 2013;136(2):021601-021601-8. doi:10.1115/1.4024917.

Carbon nanotubes are surprisingly ubiquitous in their use for renewable energy applications as well as for environmental protection and remediation. Hence, this is the motivation for the current review, to investigate into their usefulness. The characteristic properties of these nanotubes are a result of their large surface areas, and their unique mechanical, electrical, and chemical properties, and in no small part, due to its relatively easy manufacturability. Research has been done using carbon nanotubes for hydrogen storage, although it does not seem logical that carbon nanotubes would be very useful for this purpose. Carbon nanotubes used for solar collectors are used mainly for their improved thermal and electrical conductivities. Organic solar cells do not have a long life since they deteriorate in the sun. Research into long-lasting, yet inexpensive organic solar cells is an active area, and should continue to be so for some time. Carbon nanotubes are activated by certain chemicals. They may be used to react with solids, liquids, and gases. Hence, they are employed for waste water treatment, liquid, and gaseous cleanup. They may be used to remove metals as well as life pathogens. As the number of new pollutants and pathogens entering the environment multiply, research should continue to study the use of carbon nanotubes with regards prevention and remediation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):021602-021602-7. doi:10.1115/1.4025959.

A compartmental furnace model for supercritical coal-fired boiler systems is presented in this paper. Instead of the traditional lumped parameter method, the furnace is divided to seven compartments along the height based on the positions of the burner groups. The lower six compartments correspond to the six groups of burners, respectively. This model provides the possibility to connect the pulverization system and the furnace, the variability of the combustion property caused by changes of the pulverization system can be studied by switching the operating conditions. To evaluate the proposed model, simulation results are compared with available data from a 600 MW supercritical coal-fired boiler and reasonably good agreement is achieved. The simulation results also show that the compartmental model features a better precision than the lumped parameter modeling. This model allows for evaluating different control strategies and subsequently proposing optimization strategies for boiler system operation.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2013;136(2):022001-022001-7. doi:10.1115/1.4025715.

This paper presents an evaluation of the environmental performance of an advanced zero emission plant (AZEP) including CO2 capture. The evaluation is conducted with the aid of an advanced exergoenvironmental analysis. The results are compared with those of a reference combined-cycle power plant without CO2 capture. Advanced exergy-based methods are used to (a) quantify the potential for improving individual components or overall systems, and (b) reveal detailed interactions among components—two features not present in conventional analyses, but very useful, particularly when evaluating complex systems. In an advanced exergoenvironmental analysis, the environmental impacts calculated in a conventional exergoenvironmental analysis are split into avoidable/unavoidable (to evaluate the potential for component improvement) and endogenous/exogenous (to understand the interactions among components) parts. As in the reference plant, the potential for reducing the environmental impact of the AZEP has been found to be limited by the relatively low avoidable environmental impact associated with the thermodynamic inefficiencies of several of its components. However, although the environmental impacts for the majority of the components of the plant are related mainly to internal inefficiencies and component interactions are of secondary importance, there are strong interactions between the reactor and some other components.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022002-022002-6. doi:10.1115/1.4025974.

Local entropy generation in a turbulent nonpremixed jet flame (Sandia Flame D) is predicted using large eddy simulation (LES) with inclusion of entropy transport. The filtered form of entropy transport equation contains several unclosed source terms which represent irreversibilities due to viscous dissipation, heat conduction, mass diffusion, and chemical reaction. The subgrid scale (SGS) closure is accounted for by the entropy filtered density function (En-FDF) methodology to include complete statistical information about SGS variation of scalars and entropy. The En-FDF provides closed forms for the chemical reaction effects. The methodology is applied for LES of Sandia Flame D and predictions are validated against experimental data. Entropy statistics are shown to compare favorably with the data. All individual irreversible processes in this flame are predicted and analyzed. It is shown that heat conduction and chemical reaction are the main sources of entropy generation in this flame.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2013;136(2):022201-022201-7. doi:10.1115/1.4024716.

Methanol (CH3OH) and ethanol (C2H5OH) are generally called alcohol. They can be mixed with gasoline to fuel SI engine. The fuel blends of alcohol and gasoline are named gasohol. Alcohol emission characteristics and the contributions of fuel on hydrocarbon (HC) emission were experimentally investigated on a three-cylinder, electronic controlled, spark ignition JL368Q3 engine when it ran on 10 (v/v) %, 20 (v/v) %, and 85 (v/v) % methanol/gasoline and ethanol/gasoline fuel blends. Experimental results show that, the value of alcohol emission rates (g alcohol emission per kg alcohol fuel, g/kg.) is a decreasing exponential function of exhaust temperature with high correlation; regardless of the alcohol fraction in fuel blends, the CH3OH emission rate is no more than 8%, while that of C2H5OH no more than 35%. The emission rate of nonalcohol HC was one grade higher than the alcohol emission rate; the minimum HC emission rate occurs at middle and high engine loads, it is around 40% for methanol/gasoline blends and about 50% for ethanol/gasoline blends. Gasoline is the main source of HC emission of gasohol engine, methanol contributes no more than 8% while ethanol no more than 25% on HC emission.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022202-022202-7. doi:10.1115/1.4026204.

The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane–air partially premixed turbulent combustion have been studied experimentally using a constant volume combustion chamber (CVCC). The fuel–air mixture was ignited by centrally located electrodes at given spark delay times of 1, 5, 40, 75, and 110 ms. Experiments were performed for a wide range of hydrogen volumetric fractions (0% to 40%), simulated diluent volumetric fractions (0% to 25% as a diluent), injection pressures (30–90 bar), chamber pressures (1–3 bar), chamber temperatures (298–432 K) and overall equivalence ratios of 0.6, 0.8, and 1.0. Flame propagation images via the Schlieren/Shadowgraph technique, combustion characteristics via pressure derived parameters and pollutant concentrations were analyzed for each set of conditions. The results showed that peak pressure and maximum rate of pressure rise increased with the increase in chamber pressure and temperature while changing injection pressure had no considerable effect on pressure and maximum rate of pressure rise. The peak pressure and maximum rate of pressure rise increased, while combustion duration decreased with simultaneous increase of hydrogen content. The lean burn limit of methane–air turbulent combustion was improved with hydrogen addition. Addition of diluent increased combustion instability and misfiring while decreasing the emission of nitrogen oxides (NOx).

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022203-022203-10. doi:10.1115/1.4027407.

The effects that various charged electrodes, and associated electric fields, have on lifted propane flames have been investigated. Two electrodes were used to provide an electric field with potentials ranging from 0 to 11,000 V. The primary electrode was around the flame and the secondary electrode was the fuel nozzle. Electrode polarity and primary electrode location with various flame field locations (near, mid, far) were varied, resulting in a variety of flame behavior. Results show that the body force resultant from the bulk flow of formed ions, from a positively charged fuel nozzle, and grounded ring electrode, will increase flame liftoff height and, eventually, cause blowout. However, for the opposite polarity (positively charged ring electrode and grounded fuel nozzle), the flame progresses toward reattachment with increasing potentials. Observing the narrow window of flame blowout or reattachment (varying with polarity), it was observed that the lifted flame height fluctuations were increased with the presence of the grounded ring electrode, but reduced when the polarity was shifted to positive configuration (positively charged primary electrode). Flame hysteresis was observed when the ring electrode was positively charged and it was found that the hysteresis regime increased when the potential of the ring electrode was increased to 1500 V but had little changes at lower potentials. While the ring electrode was positively charged, a distinct hole was observed in the center of the flame. Several images are presented that show these flame holes that are present when the electrodes are charged.

Commentary by Dr. Valentin Fuster

Research Papers: Oil/Gas Reservoirs

J. Energy Resour. Technol. 2013;136(2):022801-022801-10. doi:10.1115/1.4025843.

The rising energy demand is causing the petroleum industry to develop unconventional oil reservoirs; however, the primary recovery factor is low in these types of reservoirs. Alternative methods to increase recovery need to be studied. This paper analyzes the impact of CO2 flooding a sector of the Elm Coulee field using reservoir modeling. The sector is two miles by two miles and consists of six original single-lateral horizontal wells. Two different reservoir models are built for the sector: a primary recovery black oil model and a CO2 flood solvent model. They are used to determine the additional recovery due to a CO2 flood. Furthermore, the CO2 flood model is executed with different scenarios to determine the best well locations and injection schemes. The models demonstrate that CO2 flooding horizontal wells in the Elm Coulee field increases production. Comparison of vertical and horizontal injection techniques indicates continuous horizontal CO2 injection is more efficient; it yields higher injection rates, and it is also beneficial for long-term recovery. Focusing on horizontal injection, the best scenario involves the practice of drilling new injectors and producers along with converting existing producers to injection wells. In order to satisfy production requirements, production wells can be drilled such that there is an injector between two producers. This type of arrangement on horizontal injection increases the field recovery factor over 15% after eighteen years of injection.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2014;136(2):022901-022901-8. doi:10.1115/1.4026093.

Scaling study of fluids displacement leads to proper understanding of pore-to-field scale flow mechanisms and correct evaluation of effectiveness of various recovery methods. Scaling study of immiscible forced gravity drainage, or gas assisted gravity drainage (GAGD), at laboratory scale and reservoir scale is considered here. Inspectional analysis (IA) is used to determine dimensionless scaling groups that characterize the fluid displacement and production mechanisms. It is found that scaling immiscible GAGD displacement in a homogeneous reservoir needs matching of five dimensionless scaling groups. For heterogeneous reservoirs, Dykstra-Parson coefficient which represents the permeability heterogeneity is also required. It is shown that none of the dimensionless groups can individually correlate the efficiency of the process. Hence, a new combined dimensionless group in reservoir scale which incorporates all the dominant forces is derived. The model is evaluated and verified by comparing its predictions with experimental results and extensive field simulations figures. The model is found reliable for fast oil recovery prediction of GAGD process after 2 pore volume injection in homogeneous and heterogeneous reservoirs and proposing their optimal production plan.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022902-022902-6. doi:10.1115/1.4026916.

Even though there have been several studies conducted by the industry on the use of different inlet devices for gas–liquid separation, there have been limited laboratory and field evaluations on the use of external piping configurations as flow conditioning devices upstream of a separator inlet. The results of a systematic study of droplet deposition and coalescence in curved pipe and pipe fittings are reported in this paper. A facility has been designed consisting of two main test sections: a fixed horizontal straight pipe section and an interchangeable 180 deg return pipe section (or curved pipe section) of the same length. Both inlet and outlet to the 180 deg return are horizontal, but the plane of the 180 deg return pipe section can pivot about the axis of the inlet horizontal pipe to an angle as much as 10 deg downwards allowing downward flow in the return section. Various pipe fittings of different radius of curvature can be installed for comparison in the 180 deg return. Fittings evaluated in this study included: 180 deg pipe bend, short elbow bend (with standard radius of curvature of 1.5D), long elbow bend (with custom radius of curvature of 6D), target tee bend, and cushion tee bend. Experiments have been carried out using water and air, and varying gas velocities and liquid loadings. In order to compare the performance of geometries, Droplet Deposition Fractions (DDF) were measured in the horizontal straight pipe section and in the 180 deg return pipe section as a measure of coalescence efficiency. The results demonstrate that higher DDF occurs for curved fittings as compared to the straight pipe section. The short elbow bend has approximately 10% DDF higher, whereas long elbow bend along with 180 deg pipe bend perform better (by 15–20% DDF) than straight pipe. It was found that the cushion tee and target tee bends can coalesce droplets at lower gas velocities but break up droplets at higher gas velocities. Additionally, no significant differences between DDF's in three different inclination angles of a curved pipe were observed. It can be concluded that 180 deg pipe bend or two 6D long radius elbow bend can serve as a droplet coalescer; a pair of cushion tees or target tees can also work as coalescers at low kinetic energy but as atomizers at high kinetic energy.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022903-022903-7. doi:10.1115/1.4026919.

Water shutoff is a commonly used method to mitigate the early breakthrough in horizontal wells. Gel is frequently used as an effective water shutoff agent in mature fields, especially for horizontal wells in recent years. However, the relevant water shutoff prediction model lacks the accurate physical description of the gelation phenomenon. Using the conventional model, which simply accounts for the gelation mechanisms, does not allow us to predict the horizontal wells performance correctly. In this paper, a newly coupled reservoir–wellbore model for horizontal wells gel water shutoff prediction is presented. A conventional gel simulator is used to simulate the gel injection process in the reservoir and then modified to predict the horizontal well performance after the treatment. The time-varying residual resistance factor model and viscosity model is developed to simulate the gel degradation process. Especially, the wellbore pressure drop calculation takes account for the non-Newtonian behavior during and after the gel injection. An explicit modular coupled scheme, which consists of reservoir modular and wellbore modular, is adopted to numerically predict the horizontal wells performance. The newly presented method not only simulates the gel injection process but also predict the water shut off performance in horizontal wells. A field horizontal water shutoff case prediction shows that the coupled modeling method can give satisfactory results to guide the water shutoff treatment.

Topics: Water , Reservoirs
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):022904-022904-8. doi:10.1115/1.4027452.

Cuttings transport is one of the most important aspects to control during drilling operations, but the effect of wellbore geometry on hole cleaning is not fully understood. This paper presents results from experimental laboratory tests where hydraulics and hole cleaning have been investigated for two different wellbore geometries; circular and a noncircular, where spiral grooves have been deliberately added to the wellbore wall in order to improve cuttings transport. Improving hole cleaning will improve drilling efficiency in general, and will, in particular, enable longer reach for extended reach drilling (ERD) wells. The experiments have been conducted as part of a research project, where friction and hydraulics in noncircular wellbores for more efficient drilling and well construction are the aim. The experiments have been performed under realistic conditions. The flow loop includes a 12 m long test section with 2" diameter freely rotating drillstring inside a 4" diameter wellbore made of concrete. Sand particles were injected while circulating the drilling fluid through the test section in horizontal and 30 deg inclined positions. The test results show that borehole hydraulics and cuttings transport can be significantly improved in a noncircular wellbore relative to a circular wellbore. Investigating the cutting transport in noncircular wellbores with available models is even more complex than for circular wellbores. Most drilling models assume circular wellbores, but in reality the situation is often different. Also, it may be possible to create noncircular wellbores on purpose, as in the present study. Such a comparative, experimental study of hole cleaning in different wellbore geometries has to our knowledge previously never been performed, and the results were obtained in a custom-made and unique experimental flow loop. The results and the experimental approach could therefore be of value for any one working with drilling.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Wells-Drilling/Production/Construction

J. Energy Resour. Technol. 2013;136(2):023101-023101-8. doi:10.1115/1.4025712.

In this paper, a new constant rate solution for asymmetrically fractured wells was proposed to analyze the effect of fracture asymmetry on type curves. Calculative results showed that for a small wellbore storage coefficient or for the low fracture conductivity, the effect of fracture asymmetry on early flow was very strong. The existence of the fracture asymmetry would cause bigger pressure depletion and make the starting time of linear flow occur earlier. Then, new type curves were established for different fracture asymmetry factor and different fracture conductivity. It was shown that a bigger fracture asymmetry factor and low fracture conductivity would prolong the time of wellbore storage effects. Therefore, to reduce wellbore storage effects, it was essential to keep higher fracture conductivity and fracture symmetry during the hydraulic fracturing design. Finally, a case example is performed to demonstrate the methodology of new type curves analysis and its validation for calculating important formation parameters.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;136(2):023102-023102-6. doi:10.1115/1.4025714.

Natural gas and oil exploration and production from shale formations have gained a great momentum in many regions in the past five years. Producing hydrocarbons from shale is challenging because of low productivity of wells. Optimal design of transverse fractures is a key to achieving successful well completion and field economics. This paper presents a simple analytical method to determine the minimum fracture spacing required for preventing fracture-merging. Result of the analytical method has been verified by a Finite Element Method for a typical fracturing condition in a shale gas formation. Field performances of shale gas wells are found consistent with what suggested by this work. The analytical method presented in this paper can replace the sophisticated solutions and time-consuming numerical simulators in calculating stresses around hydraulic fractures and identifying the minimum required fracture spacing. The method can be applied to designing of multifrac completions in shale plays to optimize placement of transverse fractures for maximizing well productivity and hydrocarbon recovery. This work provides engineers a simple tool for optimizing their well completion design in shale gas reservoirs.

Commentary by Dr. Valentin Fuster

Technology Review

J. Energy Resour. Technol. 2013;136(2):024001-024001-6. doi:10.1115/1.4025595.

A review of literature has been conducted to survey the kinetic data of low-density polyethylene (LDPE) pyrolysis. The review reveals large variations in the reported global kinetic parameters. The cause of variation has been identified to be the difference in the experimental techniques, including thermogravimetric analysis (TGA) and non-TGA methods. Even within the nonisothermal TGA data, large variations have been observed at heating rate of 20 K/min, while the variations are insignificant at lower heating rate regimes (2–10 K/min), indicating the influence of heat/mass transfer resistance controlling the kinetics. Detailed analysis revealed that most of the current techniques are unable to capture all the relevant data necessary for estimating the kinetic parameters of the aforementioned process. The outcome of this review work thrusts the need for a better experimental technique to estimate the kinetic parameters of complex reactions, such as polymer pyrolysis.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Energy Resour. Technol. 2013;136(2):024501-024501-4. doi:10.1115/1.4025799.

Liquid loading is a common problem for most of the mature gas wells. Over years, many methods have been developed to solve this problem. One of the widely used methods is plunger lift, which requires shut-in of the gas well for a period of time. Then, the well is reopened, and it is expected that the natural energy of the well will push the plunger to the surface carrying the liquid with it. Optimization of the plunger lift requires that the well be shut-in for a period of time as short as possible, followed by production of gas for as long as possible. This note examines the requirement for a successful shut-in of a well so that the well can sustain the production for a longer time. The note also discusses the condition under which the well will not sustain the production and the plunger lift will not be effective. The analysis is confirmed with several field examples, which will be shown in this note.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):024502-024502-4. doi:10.1115/1.4026917.

Stuck pipe is known to be influenced by drilling fluid properties and other parameters, such as the characteristics of rock formations. In this paper, we develop a support-vector-machine (SVM) based model to predict stuck pipe during drilling design and operations. To develop the model, we use a dataset, including stuck and nonstuck cases. In addition, we develop radial-base-function (RBF) neural network based model, using the same dataset, and compare its results with the SVM model. The results show that the performance of both models for prediction of stuck pipe does not differ significantly and both of them have highly accurate and can be used as the heart of an expert system to support drilling design and operations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2014;136(2):024503-024503-6. doi:10.1115/1.4027154.

The aim of this paper is to demonstrate the role of shading devices in the improvement of energy efficiency of buildings in hot dusty and dry tropical regions. The effect of shading in reducing the energy consumption of buildings is investigated by considering a case study of a guest house chosen because of its logical design approach to reduce thermal loads. The building plan, measurements, and details on schedules of building usage activities have been used as input data to a simulation program of the building. Based on the inputs, a thermal building model is developed in trnsys 17 simulation program and the effect of external shading on the building has been explored. It is seen that building design and orientation determine the effectiveness of shading. Movable shading over windows has a significant impact reducing temperatures by about 1.5 °C in each thermal zone. The difference in thermal energy loads of the building calculated from modeling simulations of the base case and the control case utilizing movable shading devices is approximately 8%. A programmable logic controllers (PLC)-based movable shading device has been designed to facilitate optimal shading control. The results enable us to draw inferences regarding the additional contribution of the shading factor in energy saving techniques for buildings.

Commentary by Dr. Valentin Fuster

Expert View

J. Energy Resour. Technol. 2014;136(2):024701-024701-3. doi:10.1115/1.4027260.

There is a controversy brewing for about 10 years that hydroelectric power plants are not a clean, renewable source of electricity. The current review indicates that the source of methane is not in the mechanics or mechanical design of the equipment used. The source of the methane is from nature, and man's failure to do the right thing. This methane may be reduced or completely eliminated. If this cannot be accomplished or if it is too expensive to retrofit the hydroelectric plant, then the deep water may be preprocessed (and the methane collected) before being used in the water turbine. Several methods have been introduced and discussed. Details have been omitted so that practicing engineers and other professionals can obtain funds to research and develop or invent the practical solutions suited to conditions local to the problem.

Commentary by Dr. Valentin Fuster

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