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TECHNICAL PAPERS

J. Energy Resour. Technol. 1999;121(3):145-148. doi:10.1115/1.2795973.

Transporting heavy crude oil by pipeline requires special facilities because the viscosity is so high at normal field temperatures. In some cases the oil is heated with special heaters along the way, while in others the oil may be diluted by as much as 30 percent with kerosene. Commercial drag reducers have not been found to be effective because the single-phase flow is usually laminar to only slightly turbulent. In this work we show the effective viscosity of heavy oils in pipeline flow can be reduced by a factor of 3–4. It is hypothesized that a liquid crystal microstructure can be formed so that thick oil layers slip on thin water layers in the stress field generated by pipeline flow. Experiments in a 1 1/4-in. flow loop with Kern River crude oil and a Venezuela crude oil BCF13 are consistent with this hypothesis. The effect has also been demonstrated under field conditions in a 6-in. flow loop using a mixture of North Sea and Mississippi heavy crude oils containing 10 percent brine.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):149-153. doi:10.1115/1.2795974.

This work discusses the effect of incorporating blast furnace slag (BFS) as an additive in water-based drilling fluids. The intent of this treatment is rapid development of a thin, impervious, and easily removable filter cake, thereby minimizing detrimental impact of the drilling fluid on formation productivity as opposed to previous applications of BFS in universal fluids. To evaluate the impact of BFS on filter cake properties, permeability plugging apparatus (PPA) tests and dynamic formation damage (DFD) studies were conducted. Drill-in fluids and dispersed muds were tested using varying quantities of BFS. Once a steady rate of dynamic filter cake deposition was achieved, the BFS in the filter cakes was chemically activated. The results obtained from these activation studies were compared with those obtained with no BFS and with unactivated BFS. The nature of the filter cakes was examined with an environmental scanning electron microscope (ESEM). Results obtained from the PPA tests indicate substantial decreases in initial spurt loss and filtrate volume with increasing concentration of BFS. The DFD studies substantiate the aforementioned observations and show enhancement of return permeabilities with BFS activation. ESEM studies demonstrate that BFS can consolidate filter cakes.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):154-160. doi:10.1115/1.2795975.

Looping subsea flowlines is one method being utilized for flow assurance. Looping allows the possibility of circulating chemicals and/or tools to remediate partial flowline blockages due to wax, paraffins, asphaltenes, hydrates, sand, and scale. This study considers if flow testing can provide an a priori knowledge of the presence and/or size of the partial blockage before remedial action is taken. The techniques developed are for single-phase liquid flow and can be applied during circulation operations in looped flowlines or in single-phase oil transportation lines. Using these models, a blockage map is created to indicate what size of blockage can be detected and what size of blockage can be characterized as to length and diameter of the restriction. Field-scale verification was obtained by placing fixed length and diameter partial blockages in the 9460-ft LSU flowloop (3.64-in. i.d.). Tests were conducted with liquid rates to 11 bpm (15,840 bbl/day) and pressures to 4000 psia.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):161-166. doi:10.1115/1.2795976.

This paper presents a statistical method to detect leaks in subsea liquid flowlines when the inlet flow rate measurements are unavailable and conventional mass balance techniques cannot be used. Presently, the only method used in these situations is to “predict” the inlet rate from a steady-state reservoir/wellbore model for use in a transient pipeline simulator. The purpose of this work was to examine the utility of a pressure loss model which requires only routine production data. This technique is derived from the statistical theory of estimation and testing, and treats fluctuations due to turbulence, transients, and measurement errors as statistical noise. This method compares two mean values of the pipeline resistance coefficient, R; the new updated value representing the potential leak and the old value being R without leak. Precision of the new method was demonstrated using the 9460-ft long, (3.64 in. i.d.) flowloop at LSU, with flowrates up to 10,000 bbl/day of water, and pressures up to 2400 psi. The leak was simulated by an orifice which discharged the water from the flowline into a shut-in-well. An environmental (wellhead) pressure up to 2200 psi was applied to simulate hydrostatic pressure in the deep-sea environment. The results presented in this paper show how detection of small leaks relates to the number of R measurements, leak position, and statistical noise resulting from flow rate-pressure fluctuations, transients, and measurement uncertainties.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):167-171. doi:10.1115/1.2795977.

One of the forces that act on a pig while in operation in a pipeline is that due to the layer of wax deposited on the pipeline wall. Therefore, if the motion of a pig or its cleaning efficiency are to be determined, this resistive force must be known as a function of the relevant parameters. The goal of this paper is to present a procedure for evaluating this force in situations of engineering interest. In essence, the procedure consists of the following steps: (i) determine the wax shear strength according to an experimental procedure developed for this purpose; (ii) from finite-element results, obtain the maximum stress in wax; (iii) with the foregoing information, calculate the pressure required for the pig to cause a maximum stress on wax equal to its shear strength. This pressure value is the threshold below which no wax removed can occur, according to the present simple approach. In this paper, each of these steps is described in detail and exemplified.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):172-175. doi:10.1115/1.2795978.

A new method of measuring the steam quality based on ultrasound is presented in this paper. This method is based on rigorous consideration of the steam’s thermodynamic properties. It is shown in the paper that the steam’s speed of sound depends on its quality at a given saturation temperature. Thus, the quality of the wet steam can be determined if its speed of sound is known. The speed of sound of a flowing fluid can be measured using transit-time ultrasonic meters. Field testing of a pair of customdesigned ultrasonic transducers has shown that it is feasible to measure the steam’s speed of sound. An uncertainty analysis of this new method is also presented in the paper. The analysis suggests that this method is capable of achieving a measurement accuracy of better than ±3 percentage points of the steam quality under typical oil field steam injection conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):176-182. doi:10.1115/1.2795979.

Current sinusoidal and helical buckling models are valid only for initially straight coiled tubing (CT). This paper stresses the effect of the pipe initial configuration (residual bending) on the sinusoidal and helical buckling behaviors in deviated wells. Using the conservation of energy and the principle of virtual work, new general equations are derived for predicting the sinusoidal and helical configurations of CT. These new equations reduce to those previously published when the CT is initially straight in deviated wells. Numerical examples are provided to show the effect of the initial amplitude, the inclination angle, and the size of a borehole on the sinusoidal and helical buckling behaviors of CT with the residual bending.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):183-188. doi:10.1115/1.2795980.

The mode localization phenomena in bottom-hole assemblies (BHA) used in oil-well drilling is investigated. A fully gaged stabilizer model is shown to produce weak coupling between segments of drillcollars separated by stabilizers. It is observed that in a weakly coupled BHA, small disorder in span length can cause strong mode localization. For the first time, it is demonstrated that gravity induces a stiffness disorder, which in turn causes strong mode localization in an inclined wellbore, even though no other disorder is present. The effect of localized modes for failure is presented by examining the maximum bending stresses with and without mode localization. The results show that design and operation of drillstrings should consider the possibility of mode localization for an accurate prediction of dynamic behavior.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):189-195. doi:10.1115/1.2795981.

This paper presents an analysis of a heat pump that uses a solid desiccant dehumidifier to reduce the humidity of the ambient air that flows into the evaporator, with the purpose of decreasing frost formation on the evaporator. The heat pump is analyzed by adding a dehumidifier model to a previously developed heat pump model that includes frost formation. The dehumidifier reduces the amount of energy required for evaporator defrosting, but introduces the need for energy for regenerating the desiccant. The purpose of the analysis is to search for operating conditions and optimum dehumidifier designs for which the use of the dehumidifier results in energy savings. The results show that the use of a dehumidifier may reduce energy consumption if the energetic cost of defrosting the evaporator is high. Other benefits of dehumidification include an increase of the time intervals between defrost cycles, a better stability in the conditions in the controlled space, and the potential for increased reliability and reduced maintenance of the heat pump.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):196-202. doi:10.1115/1.2795982.

An existing air-cooled binary geothermal power plant in northern Nevada is studied. The current performance of the plant is analyzed with an emphasis on the effects of seasonal climate changes. Two potential sites have been identified to improve the performance of the plant. Northern Nevada has a dry climate, particularly in hot summer months, and the temperature of cooling air can be decreased considerably by evaporative cooling. When the air temperature is decreased to the wet-bulb temperature, the decrease in the condenser temperature is determined to increase the power output by up to 29 percent. The required amount of water for this case is calculated to be about 200,000 tons per yr. Several parametric studies are performed by simulating the operation of the plant with an equation solver with built-in thermophysical property functions. It is determined that the net power output of the plant can be increased by 2.8 percent by optimizing the maximum pressure in the cycle. Also, replacing the existing working fluid isobutane by other commonly used binary fluids such as butane, R-114, isopentane, and pentane do not produce as much of an improvement in the plant performance as operating with isobutane at the optimum maximum pressure. Therefore, isobutane appears to be the best choice for this power plant.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):203-208. doi:10.1115/1.2795983.

This study investigates the utilization of waste heat from commercial process steam boilers for air conditioning using absorption cooling systems. An ammonia-water generator absorber heat exchange system was developed and modeled to use waste heat from the boiler flue gases and deliver chilled water. Based on approximately 1000 process steam boilers at an average throughput of 2000 kg/h in one metropolitan area in India, the study estimates that installation of these systems could result in annual operating cost savings of $10,200,000 in this region alone. These 1000 systems would also reduce the installed electric capacity needs by 16 MW. Annual coal consumption would decrease by 87,000 tonnes, while ash production would decrease by 39,000 tonnes. Carbon-based emissions are estimated to decrease by 176,000 tonnes. Therefore, installation of these systems on a countrywide basis and also in other developing countries with high year-round cooling loads and coal-based power generation would significantly alleviate installed power capacity shortages, conserve energy resources, and reduce greenhouse gas emissions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):209-216. doi:10.1115/1.2795984.

The structure of turbulent diffusion flames with highly preheated combustion air (air preheat temperature in excess of 1150°C) has been obtained using a specially designed regenerative combustion furnace. Propane gas was used as the fuel. Data have been obtained on the global flame features, spectral emission characteristics, spatial distribution of OH, CH, and C2 species, and pollutant emission from the flames. The results have been obtained for various degrees of air preheat temperatures and O2 concentration in the air. The color of the flame was found to change from yellow to blue to bluish-green to green over the range of conditions examined. In some cases a hybrid color flame was also observed. The recorded images of the flame photographs were analyzed using color-analyzing software. The results show that thermal and chemical flame behavior strongly depends on the air preheat temperature and oxygen content in the air. The flame color was observed to be bluish-green or green at very high air preheat temperatures and low-oxygen concentration. However, at high-oxygen concentration, the flame color was yellow. The flame volume was found to increase with increase in air-preheat temperature and decrease in oxygen concentration. The flame length showed a similar behavior. The concentrations of OH, CH, and C2 increased with an increase in air preheat temperatures. These species exhibited a two-stage combustion behavior at low-oxygen concentration and single-stage combustion behavior at high-oxygen concentration in the air. Stable flames were obtained for remarkably low equivalence ratios, which would not be possible with normal combustion air. Pollutant emission, including CO2 and NOx , was much lower with highly preheated combustion air at low O2 concentration than with normal air. The results also suggest uniform flow and flame thermal characteristics with conditioned, highly preheated air. Highly preheated air combustion provides much higher heat flux than normal air, which suggests direct energy savings and a reduction of CO2 to the environment. Colorless oxidation of fuel has been observed under certain conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):217-224. doi:10.1115/1.2795985.

Lasers find wide applications in heat treatment of engineering parts. The modeling and energy analysis of the heating process can reduce substantially the time required for process optimization and control. In the present study, three-dimensional laser heating model is introduced using an electron kinetic theory approach, the energy analysis is carried out to predict the first and second law efficiencies, and the entropy generation number is computed during the process. The equation derived for the heat conduction is in the form of an integro-differential equation, which does not yield an analytical solution. Therefore, a numerical method employing an explicit scheme is introduced to discretize the governing heat transfer equation. It is found that the electron lattice site atom collision is the determining process for the internal energy gain of the substrate in the surface vicinity. In addition, the overall entropy generation number computed in the heating cycle is less than what occurs in the cooling cycle of the heat treatment process.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(3):225-230. doi:10.1115/1.2795986.

The adoption of oxygenates in gasoline was originally spurred by the oil crises of the 1970s. In more recent years, public awareness of the environmental issues constituted the main reason for the spreading of oxygenated compounds in the transportation fuels sector. This paper describes the effects of novel nitrogen compounds in gasoline and diesel fuel on ignition quality and on pollutant emissions. Our intention is to investigate the antiknock quality, as gaged by octane and cetane determinations, of organic chemical structures mostly derivable from biomass, in combination with their effectiveness in reducing exhaust emissions under various operating conditions.

Commentary by Dr. Valentin Fuster

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