Prediction Of Long-term Performance Research Articles

Factors influencing optimum seawater reverse osmosis system designs

Potential seawater desalination applications require an evaluation of both single-stage and two-stage reverse osmosis system configurations when selecting the most cost effective process design for a specific application. The preferred reverse osmosis staging should be derived from cost factors, membrane performance parameters, feedwater characteristics and other application site-specific considerations. This paper presents a comparative analysis of single-stage and two-stage seawater reverse osmosis systems, illustrating how the optimum design is influenced by the choice of operating parameters and related cost factors. Computer aided design techniques used by Fluid Systems in evaluating reverse osmosis array options are discussed. Performance characteristics of Fluid Systems' single-stage and high-flux seawater elements are used in the analyses to arrive at the optimum system designs for a range of feedwater salinities. The approach of using pilot plant test results for long-term performance predictions is described.

Prediction of Long-Term Performance of Active Solar Heating Systems Using Daily Hours of Bright Sunshine

An algorithm based on daily hours of bright sunshine has been developed and used to evaluate the performance of active solar heating systems for different values of system parameters (collector area and efficiency curves; orientation and inclination; storage capacity; heating load). Comparisons of monthly and annual results with those obtained by other methods using measured values of global horizontal radiation show good results. The results were used to construct charts (for southern Que´bec in this case) which do not require values of solar radiation for the prediction of the system’s performance.

A Fully Implicit Hydraulic Fracture Model

Summary This paper presents some basic features of a hydraulic fracture model and a method for solving the equations for reservoir flow, fracture flow, and fracture mechanics simultaneously. A method for handling the moving-boundary problem associated with fracture propagation is given, and the method's validity is tested by use of grid sensitivity analysis. The model's capabilities are illustrated with examples involving fracture growth, fracture cleanup, and propagation and closure of a waterflood-induced hydraulic fracture. Introduction Hydraulic fracturing has been widely used to increase injectivity and productivity of wells in tight formations. The objective of this paper is to present a numerical model of the dynamic fracture process that fully couples the reservoir flow with the flow and mechanics of the fracture. The design of a fracture stimulation can be divided into three stages: prediction of fracture geometry, prediction of fracture cleanup, and prediction of long-term prediction of fracture cleanup, and prediction of long-term fractured well performance. Two popular models for predicting fracture geometry are those of Perkins and predicting fracture geometry are those of Perkins and Kern and of Geertsma and de Klerk. These models predict only two-dimensional (2D) fracture geometry, predict only two-dimensional (2D) fracture geometry, and current research is directed toward prediction of three-dimensional fracture geometry. Hagoort et al. and Settari described a simulator that can predict all three stages of the hydraulic fracturing process. They use a sequential method of solution to solve the reservoir flow equations, the fracture flow equation, and the fracture geometry equation. It is possible that the sequential method may result in small possible that the sequential method may result in small timesteps, especially during the prediction of long-term well performance. The coupling of the moving fracture tip also is handled through a complex fluid loss distribution scheme among the blocks. A fully implicit hydraulic fracture model that can simulate fracture propagation, cleanup and long-term performance is proposed. The simultaneous solution of performance is proposed. The simultaneous solution of all equations enhances the stability of the model. A rigorous treatment of the moving-boundary condition is presented. The discussion is restricted to vertical presented. The discussion is restricted to vertical fractures described by Geertsma and de Klerk's model, but the method of solution can be extended to include any other models for fracture geometry. The Physics of Hydraulic Fracturing Fracture Initiation. The equation for fracture initiation pressure pfi has been derived previously as given by pressure pfi has been derived previously as given by(1) where pinit is the initial reservoir pressure. The other terms in Eq. 1 are defined in the Nomenclature. Fracture Propagation and Closure. During fracture propagation, the pressure in the fracture is given propagation, the pressure in the fracture is given by (2)(3) where pfp = propagation pressure, pfp = propagation pressure, pfoc = fracture opening/closing pressure, pfoc = fracture opening/closing pressure, Kc = critical stress-intensity factor, and Lf = fracture half-length. To keep the fracture propagating, fluid must be inejected to maintain the fracture pressure equal to pfp, and consequently dVf/dt greater than 0, where Vf is the fracture volume. The fracture will close if pf less than pfp or dVf/dt less than 0. For 2D vertical fractures, the height is constant, and during the closing of a fracture Lf remains fixed while the width decreases. If pf drops below pfoc, the fracture will close completely. For the reopening of a fracture, the criterion proposed by Hagoort et al. and Settari was used. During the reopening process, the fracture length will not increase until the fracture pressure reaches pfp (Lfm), where Lfm, is the maximum length attained in the previous propagation phase. phase. Fracture Geometry. Geertsma and de Klerk derived the following equations for the quarter volume Vf of a vertical fracture. (4) JPT P. 1191

Some Aspects of the Prediction of Long-Term Performance of Fuel Disposal Containers

The current status of a research program to evaluate the long-term performance of metal containers for the disposal of irradiated nuclear fuel in a deep hard-rock vault is reviewed. The primary objective is to develop a container failure function which can be used in the environmental and safety assessment of the disposal concept. Both short-term and long-term container failures are discussed. It is considered that an appropriate quality assurance program should enable a realistic estimate of the number of containers that will fail prematurely. In the longer-term, failures are most likely to be caused by timedependent metal degradation.For the passive candidate container metals, i.e. titanium, nickel-base alloys, crevice corrosion is the process most likely to limit container lifetime, whereas for copper, the supply of oxidants is expected to control the corrosion rate. An experimental program to determine the behaviour of candidate metals in a range of simulated disposal vault conditions is described. This program will form the basis for credible predictions of long-term performance.

Some Aspects of the Prediction of Long-Term Performance of Fuel Disposal Containers

Some Aspects of the Prediction of Long-Term Performance of Fuel Disposal Containers

The National Research Council, Study of the Isolation System for Geologic Disposal of Radioactive Wastes

ABSTRACTThis study was conducted for the U. S. Department of Energy by the Waste Isolation Systems Panel appointed by the National Academies of Science and Engineering. The panel was charged to review the alternative technologies available for Isolating of radioactive waste in mined geologic repositories, evaluate the performance benefits from these technologles as potential elements of a waste Isolation system, and identify appropriate technical criteria for satisfactory long-term performance of a geologic repository. Conceptual repositories in basalt, granite, salt, and tuff were considered. Site-specific data on geology, hydrology, and geochemical properties were evaluated and used to define parameters for estimating long-term environmental releases, supplemented when necessary by generic properties.The technology for solid waste forms and waste packages was reviewed and evaluated. Borosilicate glass and unreprocessed spent fuel are the waste forms appropriate for further testing and for repository designs. Testing in a simulated repository environment is necessary to develop an adeauate prediction of the long term performance of waste packages in a geologic repository. Back-up research and development on alternative waste forms should be continued. The expected functions of backfill placed between the rock and waste package need clearer definition and validation.The overall criterion to be used by federal agencies in designing a geologic waste-isolation system and in evaluating its nerformance has not yet been specified. As a guideline, the panel selected an average annual dose of 10-4 sieverts to a maximally exposed individual at any future time, if the exposure is from expected events such as the slow dissolution of waste solids in wet-rock repositories and the groundwater transport of dissolved radionuclides to the biosphere. Risks from unexpected events such as human intrusion were not evaluated.Calculations were made of the long-term isolation and environmental releases for conceptual repositories in basalt, granite, salt, and tuff. The major contributors to geologic isolation are the slow dissolution of key radioelements as limited by solubility and by diffusion and convection in groundwater surrounding the waste solids, long water travel times from the waste to the environment, and sorption retardation in the media surrounding the repository. Dilution by surface water can reduce the individual radiation exposures that can result from the small fraction of the waste radioactivity that may ultimately reach the environment. Estimates of environmental releases and individual doses were made both for unreprocessed spent fuel and for reprocessing wastes.Accelerated dissolution of waste exposed to groundwater during the period of repository heating was also considered. Long-term environmental releases of radioactivity from some repositories were calculated to cause doses to maximally exposed individuals that are several orders of magnitude below the Individual dose criterion of 10-4 Sieverts per year. Other conceptual repositories were found to not meet the individual dose criterion, although these repositories could still meet the radioactivity release limits in the standard proposed by the Environmental Protection Agency.The technology for geologic waste disposal has advanced to the state of a preliminary technical plan, suitable for testing, verification, and for pllot-facility confirmation. The waste Isolation program needs a reliable prediction of long-term performance that will serve as a basis for final design, construction, licensing, and waste emplacement.

Effect of Circumsolar Radiation on Performance of Focusing Collectors

Circumsolar radiation is one of several factors, along with optical errors (contour, tracking, etc.), that determine the size and shape of the solar image at the receiver of a concentrating collector. The sensitivity of a collector to circumsolar radiation depends on insolation conditions and on collector parameters; it increases with geometrical concentration ratio and decreases with threshold. In this paper the Lawrence Berkeley Laboratory (LBL) circumsolar data are used to calculate the effect of circumsolar radiation on both the instantaneous and the long-term average performance of focusing collectors. To speed up the computations, the optical properties of the concentrator are expressed in terms of an angular acceptance function. The angular acceptance function and the brightness distribution of the sun are then convoluted, a procedure which requires, for each circumsolar scan, only 56 multiplications and additions (one for each of the angular intervals at which the brightness has been measured by the LBL circumsolar telescope). While the formalism is applicable to all focusing collectors, only parabolic troughs and dishes are evaluated explicitly in this paper. The instantaneous performance corresponding to particular circumsolar scans is of interest for the analysis of test results of collectors with high concentration. For most predictions of long-term average performance a far simpler approach will, however, be adequate. For this purpose a standard synthetic circumsolar scan has been developed that describes the brightness distribution of the solar disk (“limb darkening”) and of the circumsolar region. The radiation intercepted by a receiver is calculated once for the solar portion and once for the circumsolar portion of this standard sun shape. The long-term average radiation intercepted by the receiver is then obtained by averaging the solar and the circumsolar intercept factors, weighted according to the long-term average circumsolar ratio for the location and period under study. Tested against hour-by-hour simulations, this simple approach was found to have an rms error of only 0.2 percent, negligible compared to typical uncertainties in system performance calculations. This analysis points out the usefulness of the long-term average circumsolar ratio as a simple measure of circumsolar radiation.

Natural Analogues—A Way to Increase Confidence in Predictions of Long-Term Performance of Radioactive Waste Disposal

ABSTRACTNo exact analogue to a radioactive waste disposal system exists but by studying natural analogues of the most important components or subsystems of a waste repository, confidence in long-term predictions can be increased. The U.S. Nuclear Regulatory Commission (NRC) is supporting research on igneous intrusions into proposed repository-type host rock (basalt, tuff, crystalline hard-rock, and salt), on uranium ore body analogues, on actinide solubility as a function of natural complexing agents in closed basin lakes and on field migration of radionuclide species at low-level waste and uranium mill tailings disposal sites. The NRC is studying analogues to ensure that important parameters which might be overlooked in laboratory tests and in modeling because of problems with scaling time, space and geologic complexity can be identified and their importance bounded.

The Prediction of Long-Term Academic Performance After the Completion of a Study Skills Course

For one year after the completion of a study skills course 61 participants were followed to determine the (a) attrition rate of students who differed in personality type and previous academic achievement level, (b) level of academic performance, and (c) ability to predict academic performance from personality type, previous academic achievement, and study skills difference scores. The results showed no differences in attrition rates, significant increases in academic performance, and the factors predictive of GPA varied over time. The results suggest that factors related to academic performance may change as a function of the demands of a university environment.

Prediction of the performance of solar heating systems over a range of storage capacities

A new method for prediction of the performance of solar heating systems using well-mixed storage is presented which predicts monthly and annual system performance (relative to a computer simulation) over a wide range of system variables including minimum or base storage temperature, storage capacity, and geographic location. The method relies on heavily pre-processed site-specific radiation and weather data which is used with system properties to predict the quantities necessary for correlation. The method yields long-term monthly and annual performance predictions which are so accurate that they can serve simultaneously for preliminary design, economic optimization, and final design, eliminating the need for simulation.

Transient Tests and Long-Range Performance Predictions in Stress-Sensitive Gas Reservoirs

This paper investigates the use of a simplified stress characterization in the real-gas-potential expression and the application of "succession of steady states" techniques for test analysis and performance prediction in stress-sensitive reservoirs. The technique is shown to give good results with numerical data and with data from a laboratory model. Introduction Rising prices and declining reserves have stimulated interest in deep, low-permeability gas reserves and have added a new dimension to the interpretation of transient pressure tests. How does the well-test engineer or pressure tests. How does the well-test engineer or reservoir engineer recognize and account for stress-sensitive permeability? Fatt et al. measured this stress sensitivity permeability? Fatt et al. measured this stress sensitivity about 25 years ago and several others have presented data during the intervening years; fortunately, however, the increase in effective overburden pressure with declining reservoir pressure is not an important flow-reducing mechanism for most wells. If we consider the net confining pressure or overburden pressure to be the total overburden pressure minus the pore pressure (an assumption we will justify later), Fig. 1 will show why this is true. A normally pressured reservoir at 6,000 ft would have a net confining pressure of about 3,000 psi at discovery and 5,500 psi at abandonment. The top curve in Fig. 1 shows a permeability change of 4 percent (from 0.81 to 0.78) and the lower curve shows a change of 14 percent (from 0.58 to 0.50). The latter number is becoming percent (from 0.58 to 0.50). The latter number is becoming significant and permeability changes near the wellbore would be even greater; however, when this effect is compared with other uncertainties over the 15- to 20-year life of a gas reservoir, it probably can be ignored. However, recent data on low-permeability gas sands show much greater permeability reductions (see Fig. 2). This, along with the possibility of abnormal pressures shifting the initial net confining pressure toward the left, creates a situation where permeability changes cannot be neglected. For example, if a reservoir represented by Fig. 2 was discovered with poB= 10,000 psia, pi= 8,000 psia, and pub= 1,000 psia, the change in confining pressure would be from 2,000 to 9,000 psia over the life of the field. The permeability change would be several-fold (0.6 to 0.2 for Core I and 0.3 to 0.05 for Core H). Vairogs and Rhoades have used a numerical model to demonstrate the errors introduced into transient test analysis and long-term performance predictions. This paper attempts to simplify their theory and to eliminate paper attempts to simplify their theory and to eliminate the need for core data and a numerical model for making performance predictions. Data are presented from a performance predictions. Data are presented from a numerical model and a laboratory model to support the suggested techniques. Theory Three factors must be considered:a mathematical characterization of stress sensitivity,a nondimensional means for representing what is basically a threedimensional stress problem, andmodification of the real gas potential to include the stress-sensitive permeablility. permeablility. Permeability Characterization Permeability Characterization If we are to avoid the expensive process of obtaining laboratory, core data for every well, we must look for a means for characterizing a typical permeability reduction curve. Wyble suggested that the curves represent an exponential decline approaching a limiting value. JPT P. 1025

Prediction of long-term heat-pipe performance from accelerated life tests.

Prediction of long-term heat-pipe performance from accelerated life tests.

An Interpretation of Gasbuggy

Preliminary post-shot results of the Gasbuggy nuclear detonation gave rise to speculation in the oil industry that the shot failed to achieve the extensive fracturing forecast for the technique. Basis for this speculation is that on re-entry 1 mo after detonation, an extrapolated pressure of 977 psia at the 4,150-ft datum was encountered in contrast with an anticipated 1,050 psia. Subsequent pressure buildup was very slow. Various considerations indicate that present limited gas production from the reservoir represents widespread areal recovery of gas from parts of the ultra-tight rock matrix immediately adjacent to the interconnected fracture system. The significance of the data in interpreting pressure observations in the re-entered Gasbuggy well is that higher pressure gas from previously undrained section in and adjacent to the 440-ft radius, 14-acre, nuclear fracture region not only is pressuring up the chimney, but also is recharging the native fractured zones that were more fully depleted by past production.