Pressure Pulse Tests Research Articles

Machine Learning Provides Effective Leak Detection in Carbon Sequestration Projects

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201552, “Leak Detection in Carbon Sequestration Projects Using Machine Learning Methods: Cranfield Site, Mississippi, USA,” by Saurabh Sinha, SPE, University of Oklahoma and Los Alamos National Laboratory; Rafael Pires De Lima, Geological Survey of Brazil; and Youzuo Lin, Los Alamos National Laboratory, et al., prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5–7 October. The paper has not been peer reviewed. Saline aquifers and depleted hydrocarbon reservoirs with good seals located in tectonically stable zones make an excellent storage formation option for geological carbon sequestration.Ensuring that carbon dioxide (CO2) does not leak from these reservoirs is the key to any successful carbon capture and storage (CCS) project. In the complete paper, the authors demonstrate automated leakage detection in CCS projects using pressure data obtained from the Cranfield reservoir in Mississippi in the US. Results indicate that even simple deep-learning architectures such as multilayer feed-forward neural networks (MFNNs) can identify a leak using pressure data. Introduction Several methods that use different types of data currently are available to detect leaks. Although some of the methods are a direct indicator of CO2 presence, they cannot provide an early warning for the leaks, thus delaying remedial measures. An ideal process for the identification of leakages requires constant and repetitive comparisons of different data. Machine-learning (ML) techniques are ideally suited for this task. In this work, the authors demonstrate the use of ML techniques such as linear model, random forest, and MFNN on time-series signals obtained from a pressure-pulse test. The methodology uses the time-series data instead of 2D images or 3D voxels, thus providing a computational advantage. The authors write that an ML algorithm can distinguish between a pressure signal corresponding to a leak vs. the pressure signal corresponding to a baseline nonleak case. The trained models can then be used as an early-warning system to flag anomalous data to then be analyzed by a human interpreter. Background A pressure-pulse test uses at least two wells: an injection well and a monitoring well. The reservoir is then shocked by a series of predetermined cycles of injection and shut-ins (i.e., a pulse). The response then is recorded at the monitoring well with a pressure gauge that measures the target formation pressure. The test may be repeated with different pulses to understand the reservoir properties better. A harmonic pulse is preferred over a square wave because it allows for spectral decomposition of the pulse to analyze the reservoir response at different frequencies. Three wells are used in the study: F1, F2, and F3. Well F1 is the injector well, where alternative cycles of injection of CO2 and shut-in are carried out. Well F2 is the monitor well, which remains shut in for the duration of the test and where the pressure is monitored with the use of a pressure gauge. An artificial leak is simulated in the test by opening a surface valve at Well F3.

Experimental study on characteristics of self-excited oscillation pulsed water jet

To promote the application of self-excited oscillation pulsed water jet in various fields, various characteristics of self-excited oscillation pulsed water jet were studied experimentally. A test system of self-excited oscillation pulsed water jet characteristics was designed, and it is composed of pulsed jet producer devices, particle image velocity (PIV) measuring system, pressure pulse test device and the confining pressure cavity suitable for a PIV test. The characteristics of flow field, pressure oscillation, pulsed cavitation and acoustic shock of pulsed jet were researched. The results showed that the axis velocity vector at nozzle outlet changes periodically, and gradually becomes smaller away from the nozzle. The peak pressure of self-excited oscillation pulsed water jet is 2.5 times higher than the common continuous jet. The wave crest and the wave trough of pulsed jet are not completely symmetric. As the pump pressure increases, the length of bubble cloud increases, and it first increases and then decreases with confining pressure increasing. The vibration acceleration of sonic boom increases and then decreases as pump pressure increases, and decreases steadily with confining pressure increasing.

Detection and characterization of CO2 leakage by multi-well pulse testing and diffusivity tomography maps

Pressure pulse testing, a type of interference well testing, has shown promising applications in subsurface carbon dioxide (CO2) leakage detection and monitoring. In pressure pulse testing, a pressure signal generated by periods of injection and shut-in (from a pulsing well) propagates deep into the formation, and the corresponding response is recorded at the observation well(s). The shape of the signal alters as it travels between the pulsing well and the observation well. Analysis of this characteristic change is the basis for measurement of formation properties such as the total hydraulic diffusivity coefficient. If the test is repeated over time, one can detect and monitor temporal changes in the hydraulic diffusivity coefficient. In this paper, we used a modified analytical solution in the frequency domain to analyze the pressure pulse test data and to characterize the location and geometry of the CO2 leak. Using this technique, we first transferred the periodic pressure response to the frequency domain using the Fast Fourier Transform. Then we used a modified analytical solution to calculate the diffusivity coefficient excluding the injection rate data. The derived diffusivity coefficient for each pulse test was assigned to the midpoint between the pulsing well and the observation well. Finally, a stochastic simulation approach was used to generate a large-scale diffusivity tomography map for the target formation. When this concept was applied to a network of monitoring wells, the derived diffusivity tomography map successfully located and visualized the extent of CO2 leakage. The contour lines of the diffusivity tomography map reasonably revealed the geometry of CO2 leakage (point-source vs. line-source leakage) and when superposed on the CO2 saturation profile, showed very good agreement. Analysis of the results indicated that even a small amount of CO2 leakage in the investigation zone can have a measurable effect on the calculated diffusivity coefficient. This finding can be of great importance when early leak detection is of interest. Such information can be applied to monitor plume evolution and design a remediation process. Our study shows that the pressure pulse test analysis has the capability to monitor large areas inside the formation and to detect and characterize possible CO2 leaks with reasonable accuracy.

Automation Control System of the Pressure Pulse Testing Rig

With the development of industrial automation, people are increasingly demanding high product quality. Especially in automotive and aerospace fields, the fatigue quality of components determines the merits of the whole vehicle. Therefore fatigue performance testing has good prospects. Pressure pulse testing rig is a automatic control system. The system uses the solution which combines the virtual instrument technology with PLC controller technology. It has the ability to get the function of signal acquisition, signal analyzing, data processing and automatic control together. It enables the system to run automatically in accordance with setting commands and avoids the problem that the CNC system lacks of real-time capability and the disadvantage that the whole PLC driver control system can not meet the requirement of data acquisition and data processing. At the same time, it has both the advantages in the open CNC system and advantages in the controller system and can realize the highly efficient control.

Research on the Clothing Pressure Distribution Model of Female Lower Limbs

The excessive clothing pressure has a lot of negative effects for human physiology health, therefore the research on the clothing pressure is an important subject in the study of clothing comfort. This topic is an objective test research for women with shaping belt, there are blood pressure pulse test, circumference change test,”3 cm mark line” elongation test" and pressure test experiment which based on the intelligent virtual instrument clothing pressure testing system, using linear regression method to analyze clothing pressure distribution rule, and discuss correlation between the clothing pressure with lower limb circumference change and physiology blood pressure.

Hydraulic testing of low-permeability formations: A case study in the granite of Cadalso de los Vidrios, Spain

In recent years, the study of low-permeability geological formations has undergone considerable development. This is mainly due to the use of natural geological barriers to confine waste disposals, preventing leaking water from bringing contaminants into contact with the biosphere and the groundwater resources. In that context, the Spanish Geological Survey (IGME, Spanish acronym), supported by the National Radioactive Waste Management Agency (ENRESA, Spanish acronym) and with the technical advice of the Swedish Nuclear Fuel and Waste Management Company (SKB) designed and built a Mobile Hydrogeological Unit (UMH, Spanish acronym) for low-permeability formations characterization, which has been operational since 1997 and has been used for different purposes. Among other possibilities, the UMH allows conducting: constant transient-state flow-rate injection tests, constant-head transient-state injection tests, pseudo-stationary state injection tests, pressure fall-off tests, slug tests and pulse tests. The main objectives of this article are to describe the hydraulic characterization methodology used by IGME to carry out hydraulic tests in low permeability environment, to compare different testing methods and to summarize the results that have been obtained when characterizing the leucogranites of Cadalso de los Vidrios in Spain. The study area presents an increasing interest for granite production inside the Community of Madrid. The petrological and structural characteristics of the granite rocks and the core-samples extracted from a 200 m deep borehole investigation are described. The packer tests are conducted with the Mobile Hydrogeological Unit. The tests are interpreted with the help of analytical solutions. The main software used is Hytool, an open source matlab toolbox that provides a library of analytical solutions and a set of routines to facilitate hydraulic tests interpretation. The results allow the elaboration of a comparative analysis of the applied hydraulic tests and to define the hydraulic conductivity optimum application interval most suited for each of the used methods. Hydraulic conductivity values obtained varies from 3.20·10 − 7 m/s, for the upper weathered layer, to 2.80·10 − 12 m/s, for the test section from 97.36 to 116.15 m depth. Finally, the hydraulic conductivity values obtained in this area are compared with other case studies of granite formations around the world.

Summary of cavitation erosion investigations for the SNS mercury target

Intense proton beam-induced heating of the spallation neutron source mercury target will cause pressure spikes that lead to the formation of cavitation bubbles in the mercury. Erosion of the mercury container walls caused by violent collapse of bubbles could potentially limit its service lifetime. In-beam tests for a limited number of pulses (<1000 pulses for each test target) have demonstrated that pitting damage appears to be especially sensitive to beam intensity, surface treatment, and gas injection. Using results of off-line pressure pulse tests conducted for a million cycles or more to scale the results from limited in-beam tests, it is concluded that the mercury target will last at least two weeks at a time-averaged proton beam power level of 1 MW. However, because of remaining uncertainties, it is concluded that further research and development and target design efforts are needed to verify these conclusions and extend the target to higher operating powers and longer lifetimes.

Determining Fracture Closure Pressure in Soft Formations Using Post-Closure Pulse Testing

Summary This paper discusses the theory and application of a pressure-pulse testing technique to determine the fracture closure pressure (Pc) in soft formations. This technique is intended for use only after a data fracture has been pumped and is closed. Implementing the pulse technique post-closure rather than while the fracture is still open allows it to be used as an independent determination of Pc without diminishing the accuracy of the fluid leakoff coefficient (CL) determined from the data-fracture. Previous pulse-testing techniques1 require pumping into a fracture while it is still open. This practice reduces the accuracy of CL by altering the time necessary for the fracture to close (tc). Furthermore, previous pulse-testing techniques yield only a possible range for Pc, whereas the post-closure pulse technique yields a better-defined, singular value of Pc. The accuracy of post-closure pulse testing is validated with several field examples from a soft formation on Alaska's North Slope by comparing a definitive Pc determined using pressure decline analysis with Pc determined from post-closure pulse testing.

On Pressure Pulse Techniques for Testing Low Permeability Geological Materials and Formations

ABSTRACTThe accurate hydraulic characterization of low permeability geological materials and formations has important practical implications, such as the geological disposal of radioactive nuclear waste. In this paper, we discuss pressure pulse techniques, which are methods that are commonly adopted both in the laboratory and in situ for testing low permeability geological materials and formations. The results obtained in this study illustrate that: 1) the use of nominal values for water compressibility will lead to significant underestimation of permeability from the pressure pulse tests; 2) specific storage is also an important parameter that should be evaluated simultaneously with permeability; 3) to shorten the time required to measure low permeability in the laboratory, it is advisable to use disk-shaped specimens; 4) when a geological formation is anisotropic, the value of permeability calculated using an isotropic model is between the maximum and minimum permeabilities of the geological formation; 5) the values of permeability and specific storage derived from an in situ pressure pulse test may only reflect the hydraulic properties of the domain closely surrounding the test well. Caution should be exercised when interpreting data derived from the pressure pulse tests for the purpose of safety assessment.

Permeability of upper oceanic basement on the eastern flank of the Juan de Fuca Ridge determined with drill‐string packer experiments

We report drill‐string packer measurements of permeabilities of uppermost basement at three sites drilled during Leg 168 of the Ocean Drilling Program in 0.9‐ to 3.6‐m.y.‐old crust on the thickly sedimented eastern flank of the Juan de Fuca Ridge. Each of the holes was cased completely through the sediment section and penetrated a few meters to tens of meters into basaltic oceanic basement. The transmissivities and average permeabilities of the open‐hole basement sections were assessed using the packer to seal the hole and controlled pumping from the drillship to apply pressure pulse and constant rate injection tests. The results, namely average permeabilities of the order of 10−14 to 10−11 m2, are generally consistent with prior packer measurements in other young ocean crustal settings, but two new findings are important. First, our new results include very high values in the youngest crust yet tested, suggesting a noteworthy age dependence of the bulk permeability of uppermost basement (at the scale measured with the short‐term packer tests), ranging from about 3×1011 m2 at 0.9 m.y. to about 2×10−14 m2 at 3.6 m.y. Second, significant scale dependence of permeability is suggested by comparison to higher values inferred from (1) thermal indications of uphole flow of formation fluids at one of our sites and (2) in situ pressures and tidal loading effects recorded in long‐term formation pressures measured after the three sites were sealed with hydrologic observatories immediately following the packer measurements.

A transient pressure pulse method for the mesurement of permeability of a cement grout

The paper discusses the application of a transient pressure pulse technique for the laboratory evaluation of the permeability characteristics of a cementitious grout material with a relatively low permeability. The experimentation involves the internal pressurization of a cylindrical grout specimen with a concentric circular cavity. The time-dependent decay of the fluid pressure within the cavity is used as the basis for the computation of the permeability of the grout. The paper presents details of the experimental methodologies and the mathematical procedures which are used to evaluate the permeability. The results of a series of radial flow pressure pulse tests are used to ascertain the permeability characteristics of a cementitious grout.

Interwell seismic logging for formation continuity at the Gypsy test site, Oklahoma

The continuity logging (or in-seam) method has been used extensively in the coal industry to determine continuity. Continuity logging is an alternative approach to multiple-offset crosswell seismic measurements using guided waves propagating parallel to the layering; in particular, to determine the continuity of sand and shale stratigraphy in oil and gas fields. The present work is a study of rock physical properties and seismic data for reservoir continuity using interwell logging techniques. Processing methods are used to delineate the reservoir boundaries and to relate seismic waves with rock physical parameters. The specific application has been to identify and analyze the propagation characteristics of guided waves in the Gypsy-fluvial sandstone formation at the Gypsy test site in Oklahoma. The integration of well logs and interwell seismic data, including trapped seismic events, suggests the presence of a continuous low-velocity clean sand in the Gypsy sandstone interval. The correlation of sand and shale stratigraphy with well logs and guided waves is consistent with available pressure pulse test data, indicating that the sands are in pressure communication between the wells and that an impermeable barrier exists between the top and bottom of the sand units in the Gypsy sandstone reservoir.

Evaluation of in situ hydraulic properties of formations at great depth : K. Hayashi, T. Ito & H. Abe, Geothermal Science & Technology, 4(3), 1995, pp 145–157

The pressure decay process during the so-called pressure pulse test is analysed for evaluating in situ hydraulic properties of a formation at great depth. The present analysis takes the following factors into account, i.e., the compliance of the tubular connecting the straddle packer to the pump on the surface and anisotropy of a formation. Both of these factors have been ignored in the conventional approach, resulting in less reliable results of evaluation. Furthermore, an automatic and objective method is developed for the evaluation, instead of the manual type-curve-fitting process which has been used in the conventional method. The new method utilises a two-dimensional optimisation, where the objective function is defined as a weighted residual sum of squares of the deviation between an experimentally observed pressure decay and a reference curve of the pressure decay, i.e., a type curve, which is theoretically prepared in advance for a given set of hydraulic properties. The method was applied to pressure decay data of pressure pulse tests performed in a field test. The application result was satisfactory. Hydraulic properties would vary depending on fluid pressure in a reservoir or a formation. The present paper also discusses a method for estimating the dependence of hydraulic properties on pressure

Inverse Problem on the Evaluation of Hydraulic Properties of Rocks Deep in the Earth's Crust and Effect of Tubular Compliance

The pressure decay process during the so-called pressure pulse test is analyzed for evaluating in situ hydraulic properties of rocks deep in the earth's crust. The present analysis takes the effects of the compliance of the tubular connecting the straddle packer to the pressurizing pump and the compliance of the well bore on the pressure decay process into account; these effects are ignored in the conventional approach. The results show that the pressure decay curve is highly dependent on the tubular compliance, and, as a result, the hydraulic properties obtained using the conventional method, which assumes that the tubular is rigid against pressure, induce large errors. Based on the analysis, a new method is proposed for evaluating in situ hydraulic properties from pressure decay curves, taking the effect of the tubular compliance into account, and the method was successfully applied to a set of experimental data of the pressure pulse test performed at a geothermal model field.

A new method for the determination of in situ hydraulic properties by pressure pulse tests and application to the Higashi Hachimantai Geothermal Field

A new method is proposed to evaluate in situ hydraulic properties of formations using the so‐called pressure pulse test over short test intervals. The analysis utilizes the continuous distribution of instantaneous ring sources of fluid over the well bore surface in order to reduce the problem to a set of singular integral equations for a homogeneous and isotropic porous medium. When the ratio of the test interval length to well bore diameter is small, or the specific storage is small, the flow parallel to the well bore axis becomes significant, and the shape of the type curves obtained from the present analysis is different from that of the conventional type curves. Use of the conventional type curves should be restricted to intervals that are more than 20 times longer than the well bore diameter. Finally, the present method is applied to evaluate the in situ hydraulic properties of the Higashi Hachimantai geothermal model field of Hot Dry Rock, Tohoku University.

The Use of Tracers in Diagnosing Interwell Reservoir Heterogeneities - Field Results

A suite of "preferred" gas and water tracers is verified for field use in identifying interwell sweep problems and providing information useful to the design, control, and interpretation of a tertiary oil recovery process. Introduction In fluid injection projects, the channeling or by-passing of injected fluids through fractures and high permeability stringers results in poor reservoir sweep efficiency and low oil recovery. When the injected fluid is water, channeling problems have a less severe impact on the flood economics because water is relatively inexpensive and can be recovered and recycled through the reservoir to recover additional oil. However, many of the improved oil recovery processes employ expensive fluids, such as surfactants, micellar fluids, and solvents that must produce oil during a single pass of a relatively small volume produce oil during a single pass of a relatively small volume through the reservoir. It is important to identify and correct any serious reservoir heterogeneities that would lead to channeling and inefficient use of expensive improved recovery fluids. Some knowledge of the near wellbore reservoir heterogeneities can be derived from well logs and core permeability data. Pressure transient and pressure pulse tests are useful in detecting interwell fractures and in determining interwell communication. Other information sometimes is available from prior waterflood performance. A supportive method to determine reservoir interwell anatomy and how a reservoir would perform in an improved recovery process is to trace the interwell flow of injected water during an initial waterflood. For the past several years, the results of 20 tracer programs conducted in reservoirs undergoing programs conducted in reservoirs undergoing waterfloods, gas drives, and alternate water-solvent injection have become available to the author. These tracer programs provided a proving ground and opportunity to programs provided a proving ground and opportunity to screen the performance of numerous water and gas tracer materials. The results also helped arrive at a suite of "preferred" tracers for waterfloods and gas drives. This paper discusses the use of chemical and radioactive tracers to identify sweep problems in a tertiary miscible pilot area in West Texas, two potential micellar pilot areas in Wyoming, a Wyoming waterflood, and a hydrocarbon miscible project in Alberta, Canada. Discussion Information Obtainable From Interwell Tracing Specific information obtained from tracing the interwell flow of injected fluids through a subterranean formation and how this information is derived from the tracer data is discussed. This type of information is the objective of every oilfield tracing program and is useful in the design, control, and interpretation of subsequent tertiary oil recovery processes applied in that field. 1. Volumetric Sweep: The volume of fluid injected at an injection well to breakthrough of the traced fluid at an offset producer is indicative of the volumetric sweep efficiency between that pair of wells. Very small injected volumes to breakthrough (relative to the interwell pore volume) would indicate the existence of an interwell open fracture (or a very thin high permeability stringer) and would give an idea of the volume of that channel. Knowledge of channel volume is important to the sizing of a remedial treatment. JPT P. 1410

PREDICTION OF RESERVES AND PRODUCTION PERFORMANCE BY SIMULATION: HALIBUT FIELD

Production from Halibut began in 1970 and after seven years 44.7 megatonnes (354 million barrels) of oil have been produced from initial Halibut reserves estimated at 82.1 megatonnes (653 million barrels). Thus the field is 54% depleted and approaching the point where oil production rates will start to decline rapidly due to increasing production of formation water. The accurate prediction of this decline point in time is of critical importance in scheduling the installation of artificial lift facilities. As a result of a 1974 reservoir engineering study, which formed part of the basis for a 53% increase in estimated Halibut reserves, predictions of near term performance have proved to be reasonably accurate and substantiated a decision in 1974 to program installation of artificial lift facilities for a 1978 start-up.A significant part of the 1974 study was the comparison of reservoir performance data obtained through regular reservoir surveillance and specialized well testing programs with predictions of reservoir performance from a three-dimensional, two-phase simulation model of the field. Reservoir description parameters used in the model were varied until its performance matched actual history for the period in hand. In achieving a history match, the model was adjusted: firstly, to reflect permeabilities estimated by in situ pressure build-up and pulse tests (these values being more than twice as high as those measured in recovered core material); secondly, to simulate restricted areas of vertical communication as defined by pulse testing between different sand units; and thirdly, to match water contact rises indicated by TDT logging. Once the model was calibrated by this method it was used to predict field performance over the whole life of the field and to schedule and size additional production facility needs.Since completion of the study, two years of additional reservoir behaviour history have become available. Performance predictions made after achieving a satisfactory history match have been in good agreement with actual performance over the past two years and work is well along on facilities design and implementation.

Reservoir Limit Tests in a Naturally Fractured Reservoir - A Field Case Study Using Type Curves

Pressure buildup, interference, and pulse tests in a naturally fractured Pressure buildup, interference, and pulse tests in a naturally fractured dry gas reservoir are influenced by reservoir limits. Type curves are matched to test data to estimate drainage area and to compute porosity and permeability. Calculated porosity and permeability values compare well permeability. Calculated porosity and permeability values compare well with published data for natural fracture systems. Introduction The case studied is a dry gas reservoir in which three wells are completed. The wells are spaced 2 and 8 miles apart in a 10-mile line along the crest of an anticline with about 100 sq miles of closure (Fig. 1). The dashed contour in Fig. 1 is the drainage boundary that was initially estimated from geologic and production test data assuming a uniform gas-water contact. This drainage area is about 18 miles long and 3 miles wide. Only one productive stratigraphic unit is common to all three productive stratigraphic unit is common to all three wells. This is a naturally fractured zone of thinly bedded, clean orthoquartzites that accounts for 90 percent of deliverability at Well 1, 95 percent at Well 2, and 100 percent at Well 3. Type of completion, fractured zone thickness, and other reservoir data are presented in Table 1. No cores were taken directly from the naturally fractured orthoquartzite zone, but cores from other orthoquartzites had 2.5-percent average porosity and less. than 0.1-md permeability to air. Test data studied in this field case history have two chronological groupings:data recorded when Well 2 was completed, consisting of one pressure drawdown and four pressure buildup tests at Well 2; anddata obtained 4 years later, consisting of pressure interference at Wells 3 and 1 caused by flowing Well 2 for 450 hours, pressure buildup at Well 2 immediately following the interference test, and pulse response at Well 3 caused by pulsing Well 2. The field was never on production except to conduct pressure transient and production except to conduct pressure transient and deliverability tests. Analysis of the field tests data is organized into four sections:(1)general discussion of the pressure drawdown and buildup behavior in light of recently published well-test theory;(2)computation of porosity and published well-test theory;(2)computation of porosity and estimation of drainage area by matching the buildup data to type curves;(3)computation of porosity, permeability, and drainage area by matching the permeability, and drainage area by matching the interference data to type curves; and(4)analysis of pulse behavior in the presence of reservoir limits. General Pressure-Buildup Behavior Buildup Tests 1 through 4, recorded at completion of Well 2, are presented in Tables 2 through 5. The pressure drawdown corresponding to Buildup Test 4 is also pressure drawdown corresponding to Buildup Test 4 is also shown in Table 5. Fig. 2 is a graph of pressure as a function of the logarithm of time for the drawdown test. All four buildup tests are plotted in Fig. 3, using the technique of Horner. Pressure buildup during Test 1 becomes a linear function of the logarithm of the Horner time ratio, and extrapolates to initial pressure at infinite shut-in time. Each of the other tests plotted in Fig. 3 has an early period in which pressure is a linear function of the period in which pressure is a linear function of the logarithm of the Horner time ratio and a late period in which pressure bends upward. JPT P. 1097

On the dynamic response of EBR-II ducts to pressure pulses

An important consideration for the continued irradiation of experiments to and beyond pin failure in EBR-II is the response of the duct to a pressure pulse that may result from the rapid release of gas from a failed pin. Although all fuel element failures to date in EBR-II have been benign, typically pjn-holes or hairline cracks, the possibility of cladding bursts during transients cannot be precluded. Thus, the EBR-II project has performed numerous pressure pulse tests on subassembly duct and is continuing with analytical studies as well as additional testing. Investigations are being conducted within the fail-safe analysis framework. Correlation of the duct test results yielded an empirical relationship between the permanent deformations of a duct, and the pressure and volume of the fission gas in the fuel element. Results of the correlation are given for a number of variables including the type of gas, the cladding and duct material, the presence of internal restriction to gas flow, and whether predefected tubes of rupture discs are used to produce the pressure pulse. Preliminary dynamic stress analyses have been conducted using the one-dimensional finite element code, STRAW (Report ANL-8065, June 1974). A comparison of analytical predictions of maximum permanent duct deflection between flats and test results is presented in this paper. The analytical results are shown only for the deflection of a single flat. Since the analysis assumes an axisymmetric pressure pulse, opposing flats have equal deformation. However, in the tests the duct flat closest to the opening in the pressurized tube experienced the largest deformation. Parametric analyses have been conducted to study the influence of pulse shapes and material properties on duct deformation. Initial studies using a triangular pulse have shown that the pulse decay time and plastic hardening slope of the material have negligible influence on duct deformation. Consequently, subsequent studies used a constant decay time of 2 msec and a slope of 80 psi. Among the results discussed in the paper are the influence of peak pressure and yield strength on duct deformation for two rates of pressure rise and the influence of non-uniform pressure on duct deformation. The pressure is assumed to vary linearly from the middle of the flat to the corner. A pressure increase from a uniform 200 to 300 psi at the middle of a flat, increases the deformation by only 14 mil. These results demonstrate the importance of the pulse shape and its distribution over the duct and the material properties of the latter. Additional parametric investigations of duct deformation and dynamic stresses are being conducted. Two-dimensional finite element codes are being employed to study the fracture resistance of irradiated ducts.

INFLUENCE OF TIDAL PHENOMENA ON INTERPRETATION OF PRESSURE BUIILD-UP AND PULSE TESTS

Bottom-hole pressure tests conducted in the Kingfish oil reservoir (located in Gippsland Basin - Offshore Victoria) during 1974 and 1975 using a high sensitivity surface recording electronic bottom-hole pressure gauge indicated the presence of sinusoidal pressure oscillations in the reservor. The oscillations are of the order of 0.1 psi in amplitude and their frequency suggests that they are in some way related to tidal phenomena.Although the oscillations do not affect production, they do influence interpretation of pressure build-up and pulse tests. Interpretations of both late time pressure build-up behaviour and pulse tests of small response magnitude and long time lags are considered to be particularly susceptible to errors due to these oscillations if they are not recognized and corrected for. Interpretations of early time pressure build-up data and pulse tests of definite response and relatively short time lags are not regarded as being significantly affected.The physical mechanism causing these pressure oscillations in the reservoirs is not known. However, one of the various possible hypotheses is that the Latrobe Formation sands could be outcropping on the ocean floor at abyssal depths southeast of Kingfish and that the pressure transients generated by changes in the hydrostatic head due to surfate tides are transmitted hydraulically to the reservoir. If this hypothesis is proved to be valid it could influence pressure performance predictions of Gippsland Basin reservoirs.