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RESEARCH PAPERS

J. Energy Resour. Technol. 1982;104(2):93-95. doi:10.1115/1.3230399.

The theoretical analysis of a penny-shaped geothermal reservoir in the earth’s crust subject to linear tectonic stress gradients has been made on the basis of the three-dimensional theory of elasticity. The condition for stability of a reservoir requires K1 < Kc , where K1 and Kc are, respectively, the stress intensity factor for the opening mode and the fracture toughness of the surrounding rock. From this condition the upper critical pressure being necessary for the reservoir stability is obtained and is shown graphically.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):96-98. doi:10.1115/1.3230400.

Sharper lower bounds for the minimum spacing of thermally induced tension cracks in brittle half-planes are presented, and four previous [1] numerical estimates are improved.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):99-104. doi:10.1115/1.3230401.

The three-dimensional theoretical development of Berry and Sales [1] has been extended to bring the subsidence predictions into agreement with the British National Coal Board comprehensive set of empirical data. New elastic parameters have been determined to fit the amplitude of the ground level subsidence. An empirical correction factor was developed to account for small cavity width-to-depth ratio cases. This correction is believed to account for incomplete closure for half width-to-depth ratios below 0.3. The theory has also been modified to bring the subsidence profiles into agreement with the foregoing referenced data. The development has been used to predict subsidence for an actual U.S. coal mining case with multiple cavities. The theory was also used to predict subsidence level and profile for a recent Gulf/DOE UCG test conducted in a steeply dipping coal seam near Rawlins, Wyoming.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):105-107. doi:10.1115/1.3230386.

A characterization of the dynamic interaction between an impacting tool and rock is presented. The analysis is based on the concept of rock fracture energy and on simple representations of the amount of fracturing and energy storage in the rock during fracture propagation. The governing equations are not complicated. They contain a small number of parameters and impose minimum restrictions on the form or sophistication of the model of the impacting tool. Simulation results are shown for bit-tooth drop tests on Indiana limestone under different values of the differential pressure across the rock face and for various heights of drop. The predicted dynamic force-penetration curves, force-time, displacement-time and velocity-time histories agree well with reported Laboratory data and demonstrate that the essential elements of tooth drop loading are adequately represented by the model.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):108-120. doi:10.1115/1.3230387.

A rock drilling model is developed as a set of ordinary differential equations describing discrete segments of the drilling rig, including the bit and the rock. The end segment consists of a description of the bit as a “nonideal” transformer and a characterization of the rock behavior. The effects on rock drilling of bottom hole cleaning, drill string-borehole interaction, and tooth wear are represented in the model. Simulated drilling under various conditions, using this model, gave results which are similar to those found in field and laboratory drilling performance data. In particular, the model predicts the expected relationships between drilling rate and the quantities, weight on bit, differential mud pressure, and rotary speed. The results also suggest that the damping of the longitudinal vibrations of the drill string could be predominantly hydrodynamic as opposed to viscous. Pulsations in the mud flow are found to introduce “percussive” effects in the bit forces which seem to improve the penetration rate. However, it is known from field observations that drill pipe movements, if strong enough, may induce mud pressure surges which can cause borehole and circulation problems. Bit forces and torques are shown to be substantially coupled and the influence of certain rock parameters on variables which are measurable either at the bit or on the surface support the expectation that these signals can furnish useful data on the formation being drilled. Other results, though preliminary, show that the effects of the lateral deflections of the drill string may be large for the axial bit forces and significant for the torsional vibrations. For the latter, the unsteady nature of the rotation above the bit increases and the resistance to rotation due to rubbing contact between the drill string and the wellbore accounts for very large power losses between the surface and the bit.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):121-129. doi:10.1115/1.3230388.

The physical and chemical processes that occur typically within and around an oil sand fragment are considered when the fragment is suddenly introduced into a hot, low-uniform velocity, gaseous oxidizing stream. In this analytical study, the extent of bitumen volatilization was obtained from a consideration of the simultaneous heat and mass transfer within spherical oil sand fragments combined with a simplified cracking scheme of the heavy oil and asphaltene into coke and distillate. The resulting system of equations together with the boundary conditions arising from subjecting the fragments to hot convective streams were solved using Laplace transformation. The transient concentrations of bitumen and temperature within the fragments were then obtained under a wide range of operating conditions. The similarity of the expression obtained for the extent of bitumen volatilization to the expression derived from simplified analysis, based on a dropletlike model, was demonstrated for cases where the transient effects within the fragments were considered to be negligible. The results of the theoretical analysis show relatively good agreement with their corresponding experimental values at high stream temperatures, while they showed relatively inferior agreement at low temperatures.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):130-133. doi:10.1115/1.3230389.

A finite element model is presented which predicts radon diffusion in an n layer composite. The basis functions are obtained from an exact solution to the differential equation for a homogeneous layer. Thus the model gives the exact solution for n homogeneous layers and, by using many small layers, will give good results for any nonhomogeneous composite. The model can account for diffusion into the soil below the tailings, a finite radon concentration in the ambient and a radon source in each layer and the underlying base soil. In addition to the general matrix equation, closed form solutions are presented for some important special cases.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):134-141. doi:10.1115/1.3230390.

This paper describes the specifications recommended by the authors for buying linepipe in grades up to X-70 for wet, sour service. The linepipe is tested to verify that it is resistant to hydrogen-induced cracking (HIC). In addition, fracture control requirements are imposed so that if a failure does occur for any reason, the crack is guaranteed to self arrest, thus minimizing the consequences of the failure. Pipe meeting the specifications described in this paper is readily available from numerous European and Japanese mills.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):142-148. doi:10.1115/1.3230391.

Recent studies on the transient flow of non-Newtonian fluid in porous media have proposed new well test analysis techniques for non-Newtonian injection wells. This paper extends these new techniques to non-Newtonian injection well falloff testing. The practical use of this well test analysis method is demonstrated. The limitations of the techniques are also addressed. Exmaples of field data are used to demonstrate how this analysis can aid in well test interpretation and provide data and insight for the design and operation of enhanced oil recovery projects.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):149-156. doi:10.1115/1.3230392.

This paper presents solutions of the nonlinear partial differential equation using the Douglas-Jones predictor-corrector method for the numerical solution of nonlinear partial differential equations. The results are presented in tabular form and as semilogarithmic and log-log type-curve graphs. Graphs of dimensionless pressure versus dimensionless radius also are presented. Compared to results from analytical solutions of the linear partial differential equation, the graphs have the same shape. The error introduced by the linearizing approximation is small for many values of the flow behavior index, n , and decreases as n tends to unity. Dimensionless pressure is a linear function of dimensionless radius to the power (1–n ), near the well, as predicted by the steady-state equations. Also radius of investigation equation derived analytically agrees with results from numerical solutions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):157-161. doi:10.1115/1.3230393.

Systems analysis technqiues are applied to several well cases in order to optimize production rate and gas consumption of a continuous flow gas lift system. It is a procedure whereby various components, such as well capability, tubing size, flowline size, and separator pressure are analyzed in conjunction with the entire system in order to optimize the individual well or group of wells in a field. The solution point (node) can be taken anywhere in the system, but normally taken at the bottom or top of the well, and preferably both. Example problems will show the most logical manner to increase the flow rate, reduce the gas consumption, or both. A lowering of separator pressure to increase the flow rate may be a serious mistake. Examples will show that a more logical approach may be to increase the flowline size. In conclusion, all the individual components of a system must be analyzed in conjunction with the entire system for proper final analysis.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):162-169. doi:10.1115/1.3230394.

A completely new approach is presented to show the effect of completion parameters on high volume gas wells typical of the Gulf Coast. The solution can be summarized in graphical form and it will consider the following sections of the total producing system: 1) flow in the porous media, 2) effect of completion, and 3) flow conduit performance. The result is that the controlling parameter in the total production system can be determined. Many wells are capable of producing very high rates but are restricted due to very restricted gravel pack parameters, while wells with very efficient gravel pack completions are tubing-dominated. The procedure presented approaches the completion sensitivity analysis from a complete production system concept.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):170-173. doi:10.1115/1.3230395.

A large direct industrial refrigeration system was installed to reduce energy consumption in a chemical process plant. Electrical energy was saved by eliminating an intermediate cooling circuit including chilled liquid heat exchangers and glycol circulating pumps. A benefit of the system was increased production capacity by improving evaporator heat transfer, which reduced batch cycle time. This paper discusses system design, start-up and operating experience, and energy savings.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):174-181. doi:10.1115/1.3230396.

A series of laboratory tests was conducted using rolling contact bearings to compare the lubricating properties of a specially formulated synthetic lubricant based on diester to those of a specific mineral oil currently in service in petrochemical plant equipment. Two synthetic lubricants and two mineral oils of varying viscosities were experimentally compared. The test results indicated that the synthetic lubricant, having a viscosity of 32 m2 / s (32 cSt) at a temperature of 313K, offered longterm contact surface protection equivalent to that of the base line mineral oil which has a viscosity of 68 m2 / s, without reducing bearing service life below the theoretically predicted levels. The same good wear protection could not be achieved with a reduced viscosity mineral oil. The use of the lower viscosity synthetic lubricating fluid could provide projected energy savings of $ 75,000 per year when elements of a total petrochemical complex are considered.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1982;104(2):182-185. doi:10.1115/1.3230397.

A modified method of producing composite-holed, safety-rupture diaphragms is suggested. The influence of the proposed manufactring approach on predoming, bursting pressure, and venting action is examined.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Energy Resour. Technol. 1982;104(2):186-190. doi:10.1115/1.3230398.

Loop testing of safety devices during operation improves plant performance, reduces downtime of process-dependent rotating equipment, and enhances training of personnel. Designers, manufacturers, staff engineers, and plant personnel are always concerned with improving the efficiency and reliability of process equipment. An unscheduled shutdown caused by breakdowns or accidents involving machinery may result in millions of dollars in unrecoverable losses, because the capacity of rotating equipment has increased to a point where temporary replacements to enable the plants to continue their production are hard, or even impossible, to find. The paper will discuss how accidents may be prevented and outline a systematic approach to checking alarm and trip circuits.

Commentary by Dr. Valentin Fuster

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