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RESEARCH PAPERS

J. Energy Resour. Technol. 1986;108(2):97-106. doi:10.1115/1.3231263.

Damage detection based on changes in dynamic characteristics is considered for eight-legged k-braced steel offshore oil and gas production towers. Both experimental and analytical results are presented to improve damage detection capabilities. A 1/50th scale plastic model representing the structural system of a typical full-scale tower in 218 ft (66m) of water is used for the studies. Effects of severance of diagonal bracing members on selected vibration frequencies and mode shape parameters measurable at the deck are investigated. The effects of changes in deck mass, increase in jacket mass, and deck mass eccentricity on the selected parameters are also investigated and are shown to be different from the effects of damage.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):107-115. doi:10.1115/1.3231249.

There is a pressing need to compare and evaluate hydraulic fracture models which are now being used by industry to predict variable fracture height. The fractures of concern here are vertical fractures which have a pronounced elongation in the direction of the payzone, i.e., there is a dominant one-dimensional fluid flow along the payzone direction. A summary is given of the modeling entailed in the basic ORU fracture model, which calculates fracture height as a function of distance from the wellbore in the case of a continuous sand bounded by zones of higher (but equal) minimum in-situ stress. The elastic parameters are assumed the same in each layer, and injected flow rates and fluid parameters are taken to be constant. Leak-off is included with spurt loss, as well as non-Newtonian flow. An advantage of the model is its small computer run time. Predictions for wellbore height and pressure from the ORU model are compared separately with the AMOCO and MIT pseudo-3D models. In one instance of high stress contrast the ORU wellbore pressure agrees fairly well with the AMOCO model, but the AMOCO wellbore height is greater by 32 percent. Comparison between the ORU and MIT models in two cases (also high stress contrast) indicates height disagreement at the wellbore by factors of 1.5–2.5 with the MIT model giving a lower height. Thus it appears there can be substantial discrepancies between all three models. Next we compare the ORU model results with six cases of elongated fractures from the TERRA-TEK fully-3D model. Although two of these cases are precluded due to anomolous discrepancies, the other four cases show reasonable agreement. We make a critical examination of assumptions that differ in all the models (e.g., the effective modulus-stiffness multiplier approximation in the AMOCO model, the effect of finite fluid flow in the vertical direction in the MIT model, and the effect of 2D flow and limited perforated height in the TERRA-TEK model). Suggestions are made for reconciling some of the discrepancies between the various models. For example, the ORU/AMOCO height discrepancy appears to be resolved; for other discrepancies we have no explanation. Our main conclusion is that the AMOCO, TERRA-TEK and ORU models for fracture height and bottomhole pressure are in reasonable agreement for highly elongated fractures. Despite the difficulties in understanding the different models, the comparisons herein are an encouraging first step towards normalizing these hydraulic fracture models.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):116-119. doi:10.1115/1.3231250.

An uncoupled poroelasticity analysis of steady flow into a fixed cylindrical cavity in a porous medium gives an approximate solution for the stress field around a production casing. As compared to the open well bore case, the order of the principal stresses is inverted and larger values of the well pressure drawdown are required to initiate yielding of the porous rock. The solution quantifies the maximum formation support available from a production liner.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):120-130. doi:10.1115/1.3231251.

This paper presents new methods to analyze fractured well responses in heterogeneous reservoirs. We consider wells producing formations that are naturally fractured and use the idealizations proposed by Warren and Root (pseudosteady-state flow in the matrix-system) and by deSwaan-O (unsteady-state flow in the matrix-system) to model the naturally fractured reservoir. Pressure responses are correlated in a manner suitable for direct application of field data. Methods to determine fracture half-length are presented. Two field applications are discussed. The consequences of neglecting the heterogeneous character of the porous medium are also discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):131-139. doi:10.1115/1.3231252.

A theoretical solution of the channeling effect is presented. The details of the channeling production are investigated in detail and an approximate method for obtaining the temperature distribution is presented. These results complete a theoretical solution of the channeling effect which has a number of different applications in energy-related problems, such as fixed-bed catalytic reactors, metal processing, underground coal gasification, oil shale, chemical-reaction engineering, drying and packed-bed heat exchangers. These differential permeability problems are also encountered in several energy resource extraction applications related to underground coal conversion, vertical modified in-situ (VSIS) oil shale retortion, steam flooding and oil recovery from tar sands. The method of matched asymptotic expansions is used to obtain the theoretical solution. The effects of using the singular perturbation solution in obtaining the temperature distribution are discussed. The existence and the concept of the triple momentum boundary layer in variable porosity media is analyzed in detail. The theoretical results are found to be in good agreement with the numerical and the available experimental results.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):140-145. doi:10.1115/1.3231253.

This work examines the upward natural or forced flow of geothermal fluids in liquid-dominated wells. The objective of the project is to develop a model that would adequately describe these flows and would yield predictions of use to geothermal engineers and plant designers. The unique part of this model is that it takes into account the presence and the effect of noncondensable gases, such as CO2 , in the flow as well as the salts, such as NaCl. In the subsequent sections the two-phase flow equations are developed and solved with the help of a computer program. The results obtained agree well with experimental data and qualitative expectations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):146-155. doi:10.1115/1.3231254.

Constitutive relations for the compaction behavior of porous sandstone have been formulated to describe the results of uniaxial and triaxial tests under reservoir pressure and temperature conditions. An expression for loading behavior in uniaxial compression is derived by treating the loading modulus as an independent variable. Similar relations are derived for uniaxial and triaxial compaction tests. Elastic unloading takes a quadratic form when described by incremental stresses and strains. The constitutive equations relate the values of the incremental stress and strain on loading and unloading using parameters that are a function of the state of prestress in the material. Published data on samples cored from three different wells at various depths exhibited a similar dependence of rock properties on mechanical and pore pressure loads.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):156-160. doi:10.1115/1.3231255.

The present paper concerns the description of uniaxial deformation and failure of ice in uniaxial compression in terms of a nonlinear viscoelastic constitutive theory. The constitutive model incorporates explicit dependence upon micro-structural defect growth and assumes the form of a so-called modified superposition integral contaiing a linear kernel which depends only upon time. This last feature will greatly simplify the task of experimentally characterizing the various material properties which appear in the theory. The existence of correspondence principles for the model will also facilitate the solution of practical boundary value problems. Predictions based upon this model will be shown to agree qualitatively with experimental results for creep (constant stress) and strength (constant strain-rate) tests on ice. In addition, specific empirically deduced relationships between stress, strain, strain-rate and time at certain critical points in these standard tests will be shown to result directly from the constitutive theory as special cases.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):161-167. doi:10.1115/1.3231256.

Icebreaking technology has been improved over the last 10–15 yr so that the installed power of icebreaking ships could be drastically reduced. The improvement is demonstrated on four examples of icebreaking ships, one conventional and three advanced concepts, which have shown their icebreaking ability already in full scale. The icebreaking capability of ships is suggested to be evaluated through model tests, theoretical approach and by full-scale measurements. The evaluation should be carried out for various ice conditions by resistance and self-propulsion tests. Finally, some thoughts are presented on features of an advanced icebreaker.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):168-172. doi:10.1115/1.3231257.

Alternative bow forms have been investigated for the “M. V. Arctic” in a test program sponsored by the German Ministry for Research and Technology and the Transportation Development Centre of Transport Canada. The “M. V. Arctic” is a Canadian Arctic Class 2 bulk carrier of 28000 dwt which operates between the Northwest Territories and Europe during the summer and fall months. The tests were conducted at the Hamburg Ship Model Basin using a 1/30th scale model fitted with three different forebody forms. These included the Thyssen/Waas design, a new design by Melville Shipping Ltd., Calgary, and the existing bow form. The tests were performed in ice, still water and irregular seaway. The Thyssen/Waas icebreaker system includes a novel bow form and employs an unconventional icebreaking technique. The system has been successfully tested in model and demonstrated in full scale with the modified icebreaker “Max Waldeck”. The Melville design uses a conventional form incorporating the latest technology. This paper describes the model tests and discusses the relative performance as indicated by the test results. The investigation has shown the potential for the use of the Thyssen/Waas bow form on icebreaking cargoships such as the “M.V. Arctic”.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):173-178. doi:10.1115/1.3231258.

Experiments were performed to study the two-dimensional natural convection heat transfer from two heated isothermal horizontal cylinders to an isothermal-cooled rectangular enclosure. The experiments were designed to simulate the heat transfer encountered in underground heat distribution systems where steam and condensate lines are routed through underground or in-ground corridors (utilidors) from a central plant. The steam supply and condensate return lines were simulated with two copper cylinders. The fluid between the cylinders and enclosure was distilled water to simulate the Rayleigh number range encountered with air in actual utilidors. Results were obtained for the overall heat transfer coefficient between the two cylinders and the enclosure. The data was correlated over a Rayleigh number, RaL , range of 2.1 × 108 to 4.8 × 109 representative of the Rayleigh number, based upon a hypothetical gap width, in a typical utilidor exposed to extreme enclosure to piping temperature differential boundary conditions. The corresponding Nusselt numbers, NuL , ranged from 21 to 59 when both cylinders were heated for water as the intermediate fluid. Corresponding heat transfer coefficients calculated for the utilidor case with air as the intermediate fluid were found to be smaller compared to some other correlations for concentric cylinders.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):179-182. doi:10.1115/1.3231259.

A cold test model study of the staged cascade fluidized bed coal combustion process is described. Proper cascade flow of solids through the system was found to be sensitive to bed and downcomer distributor plate pressure drops. Control of bed depth by weir level was also complicated at high fluidization velocities by the process of entrained particles falling back into the downcomer. Bed to tube heat transfer coefficients ranging from 142 to 256W/m2 •K were measured at the top surface of a simulated boiler tube in shallow beds, 0.15 to 0.23m deep.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):183-187. doi:10.1115/1.3231260.

Information about the limits of flame propagation within streams of homogeneous gaseous fuel-air mixtures at atmospheric pressure is presented for both low velocity streams, in the presence of pilot jet flame ignition, as well as for high velocity streams when ignited by an electric spark of adequate and constant energy. In addition to methane, representing natural gas, other gaseous fuels were considered that included hydrogen and propane. The roles of the presence of varying concentration of the diluent gases, nitrogen and carbon dioxide, with the methane and changes in the intensity of turbulence were also investigated.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1986;108(2):188-193. doi:10.1115/1.3231261.

A kite-powered pump which employs a kite to convert wind energy into potential energy of water has been studied to determine its performance characteristics and see if the steady-state operation is feasible. Governing equations describing the motion of the pump in both the ascent and descent modes have been developed assuming that the tether is inflexible and that its profile is a straight line. These equations have been solved numerically to assess how performance parameters of the pump, such as output power, load-carrying capacity and cycle time vary with the pump stroke, kite weight, kite’s lift to drag ratio (CL /CD ), initial tether length and tether angle of inclination. Further, conditions for steady-state operation of the pump have been specified. The results show that (i ) the maximum power during the ascent is produced when the kite motion is approximately crosswind, (ii ) the steady-state cyclic motion of the kite pump is feasible with a net power output, (iii ) the average pump power increases at a rate slower than (CL /CD )2 as (CL /CD ) increases, and (iv ) the pump power peaks with the kite weight.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Energy Resour. Technol. 1986;108(2):194-196. doi:10.1115/1.3231262.

Flexible manufacturing systems are designed to produce a wide variety of parts with different shapes and sizes. However, the current philosophy of employing dedicated fixtures is expensive, and inefficient, and if these modern manufacturing systems are to be truly flexible, then the fixturing must be flexible also. This paper which reports on an innovative class of flexible fixtures based on particulate fluidized beds, not only presents a mathematical model governing the holding ability of this novel class of fixtured, but also summarizes the results of parametric computer studies.

Commentary by Dr. Valentin Fuster

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