Research Papers: Air Emissions From Fossil Fuel Combustion

J. Energy Resour. Technol. 2013;135(3):031101-031101-13. doi:10.1115/1.4023302.

This study reports a chemical kinetics soot model for combustion of engine-relevant fuels. The scheme accounts for both low- and high-temperature oxidation, considering their crucial role in engine combustion process. The mechanism is validated against several ignition delay times and laminar burning velocities data sets for single and mixtures of hydrocarbons. To assess the mechanism ability to predict soot precursors, formation of aromatic and aliphatic species with critical effects on soot formation is investigated for several laminar premixed and diffusion flames. The model includes soot particle inception, surface growth, coagulation, and aggregation based on the method of moments. The performance of the model is evaluated by predicting the amount of produced soot during heavy alkanes and aromatic species mixtures pyrolysis. The results are encouraging, proving this methodology to be a suitable tool to simulate the all-round combustion features of engine fuel surrogates by a single reaction model.

Commentary by Dr. Valentin Fuster

Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2013;135(3):031201-031201-7. doi:10.1115/1.4023919.

The core objective of this paper is to investigate the perspectives of “renewable fuels” mainly from an energetic point-of-view in a dynamic framework until 2050 in comparison to fossil fuels. In addition, the impact on the economic prospects of an improvement of the energetic performance is analyzed. As renewable fuels, various categories of first and second generation biofuels as well as electricity and hydrogen from renewable energy sources are considered. The most important results of this analysis are: (i) While for first generation biofuels, the relatively high share of fossil energy is the major problem, for second generation biofuels, the major problems are the low conversion efficiency and the corresponding high input of renewable feedstocks. Up to 2050, it is expected that these problems will be relieved, but only slightly. (ii) The energetic improvements up to 2050 will lead to substantial reduction of energetic losses in the well-to-tank as well as in the tank-to-wheel part of the energy service provision chain. (iii) By 2050, the total driving costs of all analyzed fuels and powertrains will almost even out. (iv) The major uncertainty for battery electric and fuel cell vehicles is how fast technological learning will take place especially for the battery and the fuel cells.

Commentary by Dr. Valentin Fuster

Research Papers: Deep-Water Petroleum

J. Energy Resour. Technol. 2013;135(3):031501-031501-4. doi:10.1115/1.4023791.

With the downturn in natural gas prices, it is vitally important to reduce the cost of drilling shale gas wells. Gas-percussion drilling has been recently employed in shale gas field development. It increases footage capacity by nearly 60%. However, wellbore erosion by the high-velocity gas has been recognized as a problem that hinders further application of the technology. This paper investigates a potential solution to the problem using a new type of flow-diverting joint (FDJ). The FDJ with exchangeable nozzles can be installed at the shoulder of the drill collar to partially bypass gas flow into the annulus between the drill pipe and open hole. Hydraulics computations with a state-of-the-art computer program indicate that this technique will allow for the use of high-gas injection rate to carry drill cuttings while reducing the gas flow rate through the drill bit. As a result, the gas velocity in the drill collar–open hole annulus can be maintained at a safe level to prevent hole erosion. The reduced gas flow rate through the drill bit also minimizes wellbore enlargement at hole bottom. Sensitivity analyses with the computer program show that the FDJ-nozzle area to bit-nozzle area ratio is directly proportional to the annulus area ratio, and the bypassed flow rate fraction remains constant as drilling progresses. This makes the FDJ system easy to design and practical to use over a long section of hole to be drilled.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2013;135(3):032001-032001-6. doi:10.1115/1.4023741.

This paper presents an artificial neural network (ANN) for forecasting the short-term electrical load of a university campus using real historical data from Colorado State University. A spatio-temporal ANN model with multiple weather variables as well as time identifiers, such as day of week and time of day, are used as inputs to the network presented. The choice of the number of hidden neurons in the network is made using statistical information and taking into account the point of diminishing returns. The performance of this ANN is quantified using three error metrics: the mean average percent error; the error in the ability to predict the occurrence of the daily peak hour; and the difference in electrical energy consumption between the predicted and the actual values in a 24-h period. These error measures provide a good indication of the constraints and applicability of these predictions. In the presence of some enabling technologies such as energy storage, rescheduling of noncritical loads, and availability of time of use (ToU) pricing, the possible demand-side management options that could stem from an accurate prediction of energy consumption of a campus include the identification of anomalous events as well the management of usage.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2013;135(3):032201-032201-4. doi:10.1115/1.4023328.

An approach to model coal combustion process to predict and minimize unburned carbon in bottom ash of a large-capacity pulverized coal-fired boiler used in thermal power plant is proposed. The unburned carbon characteristic is investigated by parametric field experiments. The effects of excess air, coal properties, boiler load, air distribution scheme, and nozzle tilt are studied. An artificial neural network (ANN) is used to model the unburned carbon in bottom ash. A genetic algorithm (GA) is employed to perform a search to determine the optimum level process parameters in ANN model which decreases the unburned carbon in bottom ash.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032202-032202-10. doi:10.1115/1.4023482.

Dual fuel engine combustion utilizes a high-cetane fuel to initiate combustion of a low-cetane fuel. The performance and emissions benefits (low NOx and soot emissions) of dual fuel combustion are well-known. Ignition delay (ID) of the injected high-cetane fuel plays a critical role in quality of the dual fuel combustion process. This paper presents experimental analyses of the ID behavior for diesel-ignited propane and diesel-ignited methane dual fuel combustion. Two sets of experiments were performed at a constant engine speed (1800 rev/min) using a four-cylinder direct injection diesel engine with the stock electronic conversion unit (ECU) and a wastegated turbocharger. First, the effects of fuel–air equivalence ratios (Фpilot ∼ 0.2–0.6 and Фoverall ∼ 0.2–0.9) on IDs were quantified. Second, the effects of gaseous fuel percent energy substitution (PES) and brake mean effective pressure (BMEP) (from 2.5 to 10 bars) on IDs were investigated. With constant Фpilot (>0.5), increasing Фoverall with propane initially decreased ID but eventually led to premature propane auto-ignition; however, the corresponding effects with methane were relatively minor. Cyclic variations in the start of combustion (SOC) increased with increasing Фoverall (at constant Фpilot) more significantly for propane than for methane. With increasing PES at constant BMEP, the ID showed a nonlinear trend (initially increasing and later decreasing) at low BMEPs for propane but a linearly decreasing trend at high BMEPs. For methane, increasing PES only increased IDs at all BMEPs. At low BMEPs, increasing PES led to significantly higher cyclic SOC variations and SOC advancement for both propane and methane. Finally, the engine ignition delay (EID), defined as the separation between the start of injection (SOI) and the location of 50% of the cumulative heat release, was also shown to be a useful metric to understand the influence of ID on dual fuel combustion. Dual fuel ID is profoundly affected by the overall equivalence ratio, pilot fuel quantity, BMEP, and PES. At high equivalence ratios, IDs can be quite short, and beyond a certain limit, can lead to premature auto-igniton of the low-cetane fuel (especially for a reactive fuel like propane). Therefore, it is important to quantify dual fuel ID behavior over a range of engine operating conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032203-032203-13. doi:10.1115/1.4024118.

The paper presents a comprehensive review of the gas turbine hybrid vehicle (GTHV) under development at the University of Roma “Sapienza.” A GHTV is an electric vehicle (traction entirely electric on 1 or 2 axles) equipped with a small turbogas operating as a range extender and –when needed- as a recharger for other auxiliaries. After a brief review of the history of the GTHV technology, a few configurations proposed in the past by different Authors are described and critically analyzed. Then, a complete feasibility assessment of a prototype configuration of a GTHV is presented and discussed in detail. Two possible implementations are studied: one for a small city car (peak power 4–8 kW) and one for a sport GT or passenger sedan (50–100 kW). All issues related to the system and component design, packaging, identification of the “optimal” hybridization ratio, performance of the conversion chain (gas turbine + batteries + electrical motor), kinetic energy recovery systems (KERS), mechanical and electric storage devices (flywheels, capacitors, advanced batteries), monitoring and control logic, compliance with the European vehicular ECE emission regulations, are explicitly addressed. One of the most important results of this analysis is though that there are several “nearly optimal” solutions and the final choice for a possible future industrialization would be dictated by manufacturing, commercial or marketing considerations. It because not only the system performance, but also the absolute and relative sizes (i.e., nameplate power) of the turbines and of the battery package depend substantially on the type of driving mission the car is required to perform. In the paper, both theoretical and practical issues are addressed, and on the basis of the analysis of the existing state of the art, it is argued that the GTHV is an environmentally friendly, technically and economically feasible product based on mature components.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2013;135(3):032901-032901-9. doi:10.1115/1.4023171.

This paper concerns on experimental investigation of biopolymer/polymer flooding in fractured five-spot systems. In this study, a series of polymer injection processes were performed on five-spot glass type micromodels saturated with heavy crude oil. Seven fractured glass type micromodels were used to illustrate the effects of polymer type/concentration on oil recovery efficiency in presence of fractures with different geometrical properties (i.e., fractures orientation, length and number of fractures). Four synthetic polymers as well as a biopolymer at different levels of concentration were tested. Also a micromodel constituted from dead-end pores with various geometrical properties was designed to investigate microscopic displacement mechanisms during polymer/water flooding. The results showed that polymer flooding is more efficient by using hydrolyzed synthetic polymers with high molecular weight as well as locating injection well in a proper position respect to the fracture geometrical properties. In addition, by monitoring of microscopic efficiency, pulling, stripping, and oil thread flow mechanisms were detected and discussed. The results showed that flow rate, fluid type, polymer concentration, and geometrical properties of pores influence the efficiency of mentioned mechanisms. Furthermore, it was detected that polymer's velocity profile play a significant role on oil recovery efficiency by influencing both macroscopic and microscopic mechanisms. This study demonstrates different physical and chemical conditions that affect the efficiency of this enhanced oil recovery method.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032902-032902-18. doi:10.1115/1.4023333.

Introducing sources of axial vibration into an oilwell drillstring has the potential to improve the drilling efficiency. Vibration generator tools, such as drillstring agitators, are under development or in current use to excite the bottom-hole assembly (BHA) axially in order to increase power and weight at the bit, improve the rate of penetration (ROP), reduce drillstring-wellbore friction, and accelerate the cutting removal process. Enhanced drilling under the effect of intentional imposed vibration is called “vibration-assisted rotary drilling” or VARD. While potentially enhancing the drilling process, VARD tools can also excite many unwanted vibration modes of the drillstring. These unwanted vibrations can cause fatigue damage and failure of BHA components such as “measurement while drilling” (MWD) tools, bit and mud motors, and consequently, inefficient drilling. This motivates a study of the complex dynamic behavior of an axially excited drillstring. Transverse vibration is the most destructive type of drillstring vibration, and the coupling between transverse and axial vibration of a drillstring subjected to an applied VARD force is of great interest to the experts in the field. In this study, the coupled axial-transverse vibration behavior of the entire drillstring under the effect of a VARD tool is investigated. A dynamic finite element method (FEM) model of the vertical drillstring assuming a multispan BHA is generated and validated with a coupled nonlinear axial-transverse elastodynamic mathematical model. The effects of mud damping, driving torque, multispan contact and spatially varying axial load are included. Geometry, axial stiffening and Hertzian contact forces are sources of nonlinearity in the model. A mesh sensitivity analysis is conducted to reduce computational time. The accuracy of the retained modes in the analytical equations is verified by extracting the total effective mass derived by the FEM model. There is agreement between the FEM and analytical models for coupled-transverse and axial vibration velocities, displacements, resonance frequencies and contact locations and behavior. While the analytical model has fast running time and symbolic solution, the FEM model enables easy reconfiguration of the drillstring for different boundary conditions, inclusion of additional elements such as shock subs, and changing the number and locations of stabilizers.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032903-032903-6. doi:10.1115/1.4023740.

In this study, simple empirical frictional pressure losses and cuttings bed thickness correlations including pipe rotation are developed for solid-liquid flow in horizontal and deviated wellbores. Pipe rotation effects on cuttings transport in horizontal and highly inclined wells are investigated experimentally. Correlations are validated experimental data with pure water as well as four different non-Newtonian fluids for hole inclinations from horizontal to 60 degrees, flow velocities from 0.64 m/s to 3.56 m/s, rate of penetrations from 0.00127 to 0.0038 m/s, and pipe rotations from 0 to 250 rpm. Pressure drop within the test section, and stationary and/or moving bed thickness are recorded besides the other test conditions. The new correlations generated in this study are believed to be very practical and handy when they are used in the field.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032904-032904-13. doi:10.1115/1.4023330.

In high-risk, high-cost environments, such as ultra-deep waters, refining advanced technologies for the successful completion of wells is paramount. Challenges are still very much associated with complex bottomhole assemblies (BHAs) and with the vibration of the drillstring when used with hole enlarging tools. These tools with complex profiles and designs become additional excitation sources of vibration. The more widespread use of downhole tools for both directional telemetry and logging-while-drilling (LWD) applications, as part of the front line data acquisition system within the drilling process, has made reliability a prime area of importance. This paper presents and validates an existing model to predict severe damaging vibrations. It also provides analysis techniques and guidelines to successfully avoid the vibration damage to downhole tools and to their associated downhole assemblies when using hole enlarging tools, such as hole openers and underreamers. The dynamic analysis model is based on forced frequency response (FFR) to solve for resonant frequencies. In addition, a mathematical formulation includes viscous, axial, torsional, and structural damping mechanisms. With careful consideration of input parameters and the judicious analysis of results, we demonstrated that drillstring vibration can be avoided by determining the three-dimensional vibrational response at selected excitations that are likely to cause them. In addition, the analysis provides an estimate of relative bending stresses, shear forces, and lateral displacements for the assembly used. Based on the study, severe vibrations causing potentially damaging operating conditions that had been a major problem in nearby wells were avoided. Steps required to estimate the operating range of the drilling parameter such as weight on bit and rotational speeds to mitigate and avoid the downhole tool failures due to vibration are given. Extensive simulations were performed to compare the data from the downhole vibration sensors; this paper includes severe vibration incidence data from three case studies in which the model estimated, predicted, and avoided severe vibration (Samuel, R., et al., 2006, “Vibration Analysis Model Prediction and Avoidance: A Case History,” Paper SPE 102134 Presented at the IADC India Conference, Mumbai, India, Oct. 16–18; Samuel, R., 2010, “Vibration Analysis for Hole Enlarging Tools” SPE 134512, Annual Technical Conference, Florence, Italy).

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032905-032905-11. doi:10.1115/1.4023331.

Solid particle erosion is a mechanical process in which material is removed from a surface due to impacts of solid particles transported within a fluid. It is a common problem faced by the petroleum industry, as solid particles are also produced along with oil and gas. The erosion not only causes economic losses resulting from repairs and decreased production but also causes safety and environmental concerns. Therefore, the metal losses occurring in different multiphase flow regimes need to be studied and understood in order to develop protective guidelines for oil and gas production equipment. In the current study, a novel noninvasive ultrasonic (UT) device has been developed and implemented to measure the metal loss at 16 different locations inside an elbow. Initially, experiments were performed with a single-phase carrier fluid (gas-sand) moving in the pipeline, and the erosion magnitudes are compared with computational fluid dynamics (CFD) results and found to be in good agreement. Next, experiments were extended to the multiphase slug flow regime. Influence of particle diameter and liquid viscosity were also studied. Two different particle sizes (150 and 300 μm sand) were used for performing tests. The shapes of the sand are also different with the 300 μm sand being sharper than the 150 μm sand. Three different liquid viscosities were used for the present study (1 cP, 10 cP, and 40 cP). While performing the UT experiments, simultaneous metal loss measurements were also made using an intrusive electrical resistance (ER) probe in a section of straight pipe. The probe in the straight pipe is an angle-head probe which protrudes into the flow with the face placed in the center of the pipe. The UT erosion measurements in a bend are also compared with experimental data obtained placing an intrusive flat head ER probe flush in a bend, and the results were found to be in good agreement. Finally, the noninvasive nano UT permanent placement temperature compensated ultrasonic wall thickness device developed for this work has the capability of measuring metal loss at many locations and also identifying the maximum erosive location on the pipe bend.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):032906-032906-7. doi:10.1115/1.4023931.

In this paper a mathematical model was developed to predict temperature profiles for two-phase oil-water stratified flows. Based on the energy balance of a control volume, analytical solutions were derived for the prediction of temperature profiles for two-phase oil/water stratified flow pattern in pipe flows. The model has been verified with a single-phase heat transfer model, which is available in most heat transfer textbooks. Two typical cases were simulated for extreme operating conditions with water cuts of 0% and 100%, respectively. This analytical model was also validated against experimental data. The test was conducted on a multiphase facility with accurate flow control devices and effective thermal treating units. The water cut was set at 50% for this test. The simulation results and experimental data agree within the experimental uncertainty. The closure relationships can be conveniently applied to a two-phase oil/water paraffin deposition model, which is dependent on the heat transfer process. The model was also used to predict the temperature profiles for two-phase oil and water flows with different water cuts.

Commentary by Dr. Valentin Fuster

Research Papers: Natural Gas Technology

J. Energy Resour. Technol. 2013;135(3):033101-033101-7. doi:10.1115/1.4024044.

Microhole coiled tubing drilling is a new technology that provides many added advantages but at the same time poses numerous operational challenges. This manifests itself in a number of ways, all of which adversely affect the efficiency of the drilling process. These problems include increased wellbore friction, poor hole-cleaning, tubular failures, and associated problems during tripping operations. Presently conventional torque and drag models are used to calculate drag forces and surface loads during microhole coiled tubing drilling. However, these estimates might be under conservative. Therefore, an improved model and more comprehensive analysis are required. Conditions expected during microhole coiled tubing drilling are completely different from those encountered during conventional drilling. Further complexity is added when the wellbore is undulated. This paper describes a new analytical model for estimating drag forces by assuming that pipe in the horizontal portion follows a sine function wave due to residual bends and snubbing force. In addition, the model takes into account when the wellbore is also tortuous. Fluid viscosity (an important force in the microhole) is also included so we can calculate appropriate surface loads in addition to drag. This study concludes that besides wellbore inclination, curvature, and wellbore torsion, parameters such as wavelength and contact area also influence the results. This paper documents the comparison between the predicted mathematical simulation results with actual data from wells describing the accuracy and applicability of the model. The analysis results and comparison are presented along with three examples (Zhang et al., 2013, “Analytical Model to Estimate the Drag Forces for Microhole Coiled Tubing Drilling,” Society of Petroleum Engineers, Paper No. SPE 163480.).

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Energy Resour. Technol. 2013;135(3):034501-034501-3. doi:10.1115/1.4023744.

Analysis of the two-dimensional (2D) distribution of excited Ar atoms has been made to synthesize better anode materials for lithium-ion batteries. The 2D visualization of excitation temperatures was based on the “two-line” method, which are important to diagnose the plasmas used for the preparation of carbonaceous materials by plasma enhanced chemical vapor deposition. The results showed that the excitation temperature in N2-rich (CH4-lean) plasma was lower than that in N2-lean (CH4-rich), and is attributed to different excitation and reaction mechanisms of CH4 and N2.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):034502-034502-4. doi:10.1115/1.4024028.

Multicomponent synthetic gas (syngas) mixtures produced from the gasification of coal, low grade fuel, wastes, and biomass offers a novel source of hydrogen production. Gasification also eliminates much of the pollutant emissions from the combustion these fuels. Palladium based membranes offer a promising method for extracting hydrogen from syngas. Experimental results are presented from a laboratory scale experimental facility. This facility was designed and built to examine various types of palladium and palladium alloy membranes for harvesting hydrogen from the syngas. The thin membranes (on the order of ∼12 μm) examined were supported on porous stainless-steel. A mixture of pure gasses consisting of hydrogen, nitrogen, and carbon dioxide were used to simulate syngas of different composition. The specific focus was on evaluating the role of operational temperature and pressure of membrane on the separation efficiency of hydrogen. Results are reported at temperatures from 325 °C to 400 °C and pressures from 5 to 30 psi (gauge) for various concentrations of hydrogen in the gas mixture. Results showed permeation to increase by up to 33% with a 75 °C increase in temperature. Permeation increased by over 50% with an increase in partial pressure of hydrogen by only 10 psi. These results provide clean hydrogen recovery from syngas obtained from gasification and pyrolysis of wastes and biomass.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2013;135(3):034503-034503-5. doi:10.1115/1.4024120.

In situ monitoring of chemical species from the combustion pulverized coal in high-temperature air is examined using several different spectroscopic diagnostic at different equivalence ratios. Two-dimensional (2D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the temperatures to range from low to 1400 °C under various conditions of fuel-lean, stoichiometric, and fuel-rich. The highest temperature and flame stability were obtained under fuel-lean combustion condition. The chemical species generated from within the combustion zone were analyzed from the spontaneous emission spectra of the flame in the Ultraviolet–visible (UV-Vis) range. The spatial distribution of NO, OH, and CN were identified from the spectra. The 2D distribution of emission intensity visualized and recorded for NO, OH, and CN revealed high-temperatures close to the root of the flame that rapidly dispersed radially outward to provide very high temperatures over a much larger volume at further downstream locations of the flame.

Commentary by Dr. Valentin Fuster

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