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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Trade magazines and review articles describe MWD in casual terms, e.g., positive versus negative pulsers, continuous wave systems, drilling channel noise and attenuation, in very simple terms absent of technical rigor. However, few truly scientific discussions are available on existing methods, let alone the advances necessary for high-data-rate telemetry. Without a strong foundation building on solid acoustic principles, rigorous mathematics, and of course, fast, inexpensive and efficient testing of mechanical designs, low data rates will impose unacceptable quality issues to real-time formation evaluation for years to come. This all-new revised second edition of an instant classic promises to change all of this. The lead author and M.I.T.-educated scientist, Wilson Chin, has written the only book available that develops mud pulse telemetry from first principles, adapting sound acoustic principles to rigorous signal processing and efficient wind tunnel testing. In fact, the methods and telemetry principles developed in the book were recently adopted by one of the world's largest industrial corporations in its mission to redefine the face of MWD. The entire engineering history for continuous wave telemetry is covered: anecdotal stories and their fallacies, original hardware problems and their solutions, different noise mechanisms and their signal processing solutions, apparent paradoxes encountered in field tests and simple explanations to complicated questions, and so on, are discussed in complete "tell all" detail for students, research professors and professional engineers alike. These include signal processing algorithms, signal enhancement methods, and highly efficient "short" and "long wind tunnel" test methods, whose results can be dynamically re-scaled to real muds flowing at any speed. A must read for all petroleum engineering professionals!
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Contents
Cover
Title page
Copyright page
Preface
Acknowledgements
Chapter 1: Stories from the Field, Fundamental Questions and Solutions
1.1 Mysteries, Clues and Possibilities.
1.2 Paper No. AADE-11-NTCE-74 – “High-Data-Rate MWD System for Very Deep Wells.” Significantly expanded with additional photographs and detailed annotations.
1.3 References.
Chapter 2: Harmonic Analysis: Six-Segment Downhole Acoustic Waveguide
2.1 MWD Fundamentals.
2.2 MWD Telemetry Concepts Re-examined.
2.3 Downhole Wave Propagation Subtleties.
2.4 Six-Segment Downhole Waveguide Model.
2.5 An Example: Optimizing Pulser Signal Strength.
2.6 Additional Engineering Conclusions.
2.7 References.
Chapter 3: Harmonic Analysis: Elementary Pipe and Collar Models
3.1 Constant area drillpipe wave models.
3.2 Variable area collar-pipe wave models.
3.3 References.
Chapter 4: Transient Constant Area Surface and Downhole Wave Models
4.1 Method 4-1. Upgoing wave reflection at solid boundary, single transducer deconvolution using delay equation, no mud pump noise (Software reference, XDUCER*.FOR).
4.2 Method 4-2. Upgoing wave reflection at solid boundary, single transducer deconvolution using delay equation, with mud pump noise (Software reference, HYBRID*.FOR).
4.3 Method 4-3. Directional filtering – difference equation method requiring two transducers (Software reference, 2XDCR*.FOR).
4.4 Method 4-4. Directional filtering – differential equation method requiring two transducers (Software reference, SAS14D*.FOR, Option 3 only).
4.5 Method 4-5. Downhole reflection and deconvolution at the bit, waves created by MWD dipole source, bit assumed as perfect solid reflector (Software reference, DELTAP*.FOR).
4.6 Method 4-6. Downhole reflection and deconvolution at the bit, waves created by MWD dipole source, bit assumed as perfect open end or zero acoustic pressure reflector (Software reference, DPOPEN*.FOR).
4.7 References.
Chapter 5: Transient Variable Area Downhole Inverse Models
5.1 Method 5-1. Problems with acoustic impedance mismatch due to collar-drillpipe area discontinuity, with drillbit assumed as open-end reflector (Software reference, collar-pipe-open-16.for).
5.2 Method 5-2. Problems with collar-drillpipe area discontinuity, with drillbit assumed as closed end, solid drillbit reflector (Software reference, collar-pipe-closed-*.for).
5.3 References.
Chapter 6: Signal Processor Design and Additional Noise Models
6.1 Desurger Distortion
6.2 Downhole Drilling Noise.
6.3 Attenuation Mechanisms (Software reference, Alpha2, Alpha3, MWDFreq, datarate).
6.4 Drillpipe Attenuation and Mudpump Reflection (Software reference, PSURF-1.FOR).
6.5 Applications to Negative Pulser Design in Fluid Flows and to Elastic Wave Telemetry Analysis in Drillpipe Systems.
6.6 LMS Adaptive and Savitzky-Golay Smoothing Filters (Software reference, all of the filters in Sections 6 and 7 are found in C:\MWD-06).
6.7 Low Pass Butterworth, Low Pass FFT and Notch Filters.
6.8 Typical Frequency Spectra and MWD Signal Strength Properties.
6.9 References.
Chapter 7: Mud Siren Torque and Erosion Analysis
7.1 The Physical Problem.
7.2 Mathematical Approach.
7.3 Mud Siren Formulation.
7.4 Typical Computed Results and Practical Applications.
7.5 Conclusions.
7.6 References.
Chapter 8: Downhole Turbine Design and Short Wind Tunnel Testing
8.1 Turbine Design Issues.
8.2 Why Wind Tunnels Work.
8.3 Turbine Model Development.
8.4 Software Reference.
8.5 Erosion and Power Evaluation.
8.6 Simplified Testing.
8.7 References.
Chapter 9: Siren Design and Evaluation in Mud Flow Loops and Wind Tunnels
9.1 Early Wind Tunnel and Modern Test Facilities.
9.2 Short Wind Tunnel Design.
9.3 Intermediate Wind Tunnel for Signal Strength Measurement.
9.4 Long Wind Tunnel for Telemetry Modeling.
9.5 Water and Mud Flow Loop Testing.
9.6 References.
Chapter 10: Advanced System Summary and Modern MWD Developments
10.1 Overall Telemetry Summary.
10.2 Sirens, Turbines and Batteries.
10.3 References.
Chapter 11: MWD Signal Processing in China
Chapter 12: Sensor Developments in China
12.1 DRGDS Near-bit Geosteering Drilling System.
12.2 DRGRT Natural Azi-Gamma Ray Measurement.
12.3 DRNBLog Geological Log.
12.4 DRMPR Electromagnetic Wave Resistivity.
12.5 DRNP Neutron Porosity.
12.6 DRMWD Positive Mud Pulser.
12.7 DREMWD Electromagnetic MWD.
12.8 DRPWD Pressure While Drilling.
12.9 Automatic Vertical Drilling System – DRVDS-1.
12.10 Automatic Vertical Drilling System – DRVDS-2.
Chapter 13: Sinopec MWD Research
13.1 Engineering and Design Highlights.
13.2 Credits.
Chapter 14: Gyrodata MWD Research
14.1 Short and Long Wind Tunnel Facilities.
14.2 Credits.
Chapter 15: GE Oil & Gas MWD Developments (BakerHughes, a GE Company)
15.1 Recent Patent Publications.
15.2 Credits.
15.3 References.
Chapter 16: MWD Turbosiren – Principles, Design and Development
16.1 Background and Motivation.
16.2 Prototype Turbosirens and Experimental Notes
16.3 Pressure Measurement – Subtleties and Ideas.
16.4 Credits.
16.5 References.
Chapter 17: Design of Miniature Sirens
17.1 Siren flowmeter applications.
17.2 Mini-siren prototypes.
17.3. Cardboard test prototyping.
17.4 Credits.
Chapter 18: Wave-Based Directional Filtering
18.1 Background.
18.2 Theory and Difference-Delay Equations.
18.3 Calculated Results.
18.4 Conclusions.
18.5 References.
Cumulative References
Index
About the Author
End User License Agreement
Guide
Cover
Copyright
Contents
Begin Reading
List of Tables
Chapter 16
Table 16.1. Detailed sirens-in-series test data (un-tapered side edges for all above data).
Table 16.2. Turbosiren frequency and Δp versus GPM test matrix and results (different rotor cross-sections shown at left).
Table 16.3. Axial turbine data.
Table 16.4. Siren (top) and turbine (bottom) stall torque comparisons.
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Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106
Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])
Measurement While Drilling (MWD) Signal Analysis, Optimization, and Design
2nd Edition
Wilson C. Chin
This edition first published 2018 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA © 2018 Scrivener Publishing LLC For more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data ISBN 978-1-119-47915-4
Preface
The physical theories behind Measurement-While-Drilling design should be rich in scientific challenges, engineering principles and mathematical elegance. To develop the next generation of high-data-rate tools, these must be understood and applied unfailingly without compromise. But one does not simply peruse the latest petroleum books, state-of-the-art reviews, or the most recent patents to understand their teachings. Most descriptions are just wrong. The science itself does not exist. All simply rehash hearsay and misconceptions that have proliferated for more than three decades – recycled street narratives and folklore about sirens, positive and negative pulsers, and yes, mud attenuation; over-simplified product brochures from oil service companies that monopolize the industry; and, unfortunately, all preach the same complaints about low data rates and industry’s failure to address modern logging needs.
The truth is, there have been no substantive developments in MWD telemetry and design over the years. Not one paper has appeared that deals with telemetry in a manner worthy of scientific publication. New tools, more like muscle-machines than intelligent instruments, are designed without regard for acoustic concepts, while signal optimization and surface processing, more often than not based on “hand-waving” arguments, proceed without guidance from wave equation models. True, tools are better engineered; mechanical parts erode less, pulser modulation is controlled more reliably, high-powered microprocessors have replaced simple circuit boards, electronic components survive higher temperatures and pressures, and overall reliability is impressive, all of which enables the logging industry to reach deeper targets. However, these are incremental improvements unlikely to change the big picture. And the big picture is bleak: unless conceptual breakthroughs are made, the present low datarate environment is likely to persist.
Through this rapid progress, several disturbing problems are apparent. The author, having consulted for established as well as start-up companies over the past twenty years, is aware of no comprehensive theory addressing MWD acoustics. There are no university courses developed to educate the next generation of telemetry designers. The one-dimensional wave propagation models that are available are no more sophisticated that organ acoustics formulas from Physics 101. And tight-lipped service companies have been reluctant to publicize their failings, for obvious reasons, a business decision that has stymied progress in an important commercial endeavor. But unless companies are willing to share ideas and experiences, no one will benefit.
All of this is not new to science and certainly not unique to the commercialization of new products. The aerospace industry, decades ago just as subdued and secretive, suffered from similar failings. In that era though, just as the author completed his Ph.D. from the Massachusetts Institute of Technology in aerospace engineering, companies like Boeing, Lockheed and McDonnell-Douglas, for instance, finally recognized that the best way forward was free dissemination of scientific methods and ideas. Engineers openly carried their Fortran decks from one company to the next, published their findings in open journals and debated their ideas with new-found colleagues near and far. Increased employment mobility only increased idea dissemination more rapidly. The rest is history: the Space Shuttle, the Space Station, the 767, 777 and 787. It is in this spirit that the present book is written: intellectual curiosity and honesty and a genuine interest to see MWD data rates improve.
The author, no new-comer to MWD, earned his stripes at Schlumberger and Halliburton, managing MWD telemetry efforts that developed and refined new hardware concepts and signal processing techniques. However, research funding was fragmented and scientific objectives were unclear. Knowing the right questions, it is understood, solves half the problem. But it was not until the new millenium that progress in the formulation and solution of rigorous wave equation models took hold. Numerical models, notorious for artificial dissipation and dispersion, that is, phase error, were abandoned in favor of more challenging exact analytical solutions. Physical principles could, for once, be clearly understood. New methods to model acoustic sources were developed and special studies were initiated to define broad classes of noise together with the requirements for their elimination. New experimental procedures based on acoustics models were designed, as were special “short” and “long wind tunnels” that accommodated subtle physical mechanisms newly identified.
Theories and models, even the most credible, can be incorrect. In the final analysis, well designed experiments are needed to validate or disprove new ideas. In this regard, China National Petroleum Corporation (CNPC) offered to build laboratory facilities, test siren designs, educate staff and evaluate new telemetry methods, and importantly, to share its results and technology openly with the petroleum industry.
A comprehensive project overview was first presented by CNPC authors in “High-Data-Rate Measurement-While-Drilling System for Very Deep Wells,” Paper No. AADE-11-NTCE-74, at the American Association of Drilling Engineers’ 2011 AADE National Technical Conference and Exhibition, Houston, Texas, April 12-14, 2011. The paper summarized key ideas and results, but given page limits, could not provide details. All theoretical and experimental methods are now explained and summarized in this book, with numerous examples, providing useful tools to students and designers alike – our signal processing methods, dealing with signal reflection, distortion and optimization, are formulated, solved, validated and described for the first time.
In addition, we offer a new prototype roadmap for high-data-rate MWD that has found strong support from knowledgeable industry professionals. Since publication of the above paper, numerous commercial drivers have made high data-rate telemetry needs increasingly urgent. In the “old days,” conventional well logging data, e.g., resistivity, sonic or positioning, was simply transmitted to the surface for monitoring and evaluation. However, recent trends call for near-bit geosteering and rotary-steerable capabilities, in support of real-time economic and pore and annular pressure measurements. Despite their importance, few industry publications or websites provide “behind the scenes” descriptions of tool and software development processes, offering little to newer engineers eager to understand the technology – an unfortunate circumstance occurring even as the industry’s “great crew change” takes place.
To fill this need, China National Petroleum Corporation (CNPC) had encouraged us to document in detail its engineering processes, new tools and well logging sensors, in a comprehensive collection of laboratory and field photographs. Much of this work parallels ongoing developments in the West and sheds considerable insight into the country’s efforts to embrace high technology, e.g., stealth fighters, moon missions, fast computers and deep-sea submersibles, and its new-found open-ness in sharing its intellectual property. This book captures the spirit of MWD engineering in China – we also provide recent paper abstracts and describe advanced sensor development activities.
Importantly, since the appearance of first edition of this book, other organizations have adopted our ideas and methods, among them Gyrodata, GE Oil & Gas, Sinopec and others. It is the author’s hope that the newer insights offered in the following chapters will contribute to the industry’s expertise in developing more sophisticated and reliable telemetry devices. We have developed an exciting technology and are confident that the best is yet to come.
Wilson C. Chin, Ph.D., M.I.T. Houston, Texas Email: [email protected] Phone: (832) 483-6899
Acknowledgements
The author gratefully acknowledges the insights, experiences and friendships he has acquired during his numerous MWD activities over the years with Schlumberger, Halliburton, GE Oil & Gas, China National Petroleum Corporation, Sinopec and others – pleasant memories that much more than compensate for the frustrations and sleepless nights brought upon by the challenges of high data rate telemetry.
What started as a simple wind tunnel long ago, constructed from plastic tubing, a squirrel cage blower and several balsa wood models, has evolved into a useful technology with a life of its own – one that will no doubt benefit the petroleum industry for years to come. The work reported here would not have been possible without the dedication and contributions of many talented people, among them,
Professor Yinao Su, Academician, Chinese Academy of Engineering, and his able colleagues Limin Sheng, Lin Li, Hailong Bian and Rong Shi with Drilling Engineering at the China National Petroleum Corporation (CNPC) in Beijing,
Shan Li, Hai Ma and Jin Zhou Yang, with MWD Research at Sinopec Shengli Oilfield in Dongying,
Professor Wenxiao Qiao, with the Chinese University of Petroleum, in Dongying and Beijing,
Stephen Bonner, Marcus Cantu, Robert Jan, Onyemelem Jegbefume, Rob Kirby, Adrian Ledroz, Eugene Linyaev, James Riley, John Rogers, Siddharth Shah, Rob Shoup and Gary Uttecht with Gyrodata in Houston,
Stewart Brazil, Kamil Iftikhar, Jihan Jiang, Paul Reeves and Shadi Saleh with GE Oil & Gas in Houston, and last but not least,
Jose Trevino and Larry Leising, previously with Schlumberger, who introduced this author to MWD technology and importantly guided his initial work more than two decades ago.
Phillip Carmical, Acquisitions Editor and Publisher, has been extremely supportive of this book project and others in progress. His philosophy, to explain scientific principles the way they must be told, with equations and algorithms, is refreshing in an environment often shrouded in secrecy and commercialism. I have known Phil for some twenty years – through it all, he has been encouraging and optimistic, and a pleasure to work with. His appreciation for technology and the role that rigorous science plays in the petroleum industry has made a positive difference in my own work and the way I have been able to contribute to several geoscience specialties. Phil is great to work with and it is my hope that our collaboration continues far into the future.
Finally, I wish to thank Xiaoying “Jenny” Zhuang for her hard work and commitment to ably working both sides of the language barrier in my communications with overseas colleagues at CNPC, CNOOC/COSL, Sinopec and several petroleum universities. Without her interpretation skills and willingness to learn and understand MWD design issues, our efforts would not have yielded the successes that they have and would not have led to friendships and lasting memories. And without Jenny’s personal devotion to a cause, this book would never have seen publication – and who knows, low data rates may remain just that.
Wilson Chin Houston, Texas and Beijing, China May 2018
Chapter 1Stories from the Field, Fundamental Questions and Solutions
This chapter might aptly be entitled “Confessions of a confused, high-tech engineer.” And here’s why. In my previous reincarnation, I was Manager, Turbomachinery Design, at Pratt & Whitney Aircraft, United Technologies Corporation, the company that supplied the great majority of the world’s commercial jet engines. Prior to that, I had served as Research Aerodynamicist at Boeing, working with pioneers in computational fluid dynamics and advanced wing design. What qualified me for these enviable positions was a Ph.D. from the Massachusetts Institute of Technology in acoustic wave propagation – and I had joined a stodgy M.I.T. from its even stodgier cross-town rival, the California Institute of Technology. These credentials in acoustics and fluid mechanics design made me eminently qualified to advance the state-of-the-art in Measurement-While-Drilling (also known as, “MWD”) telemetry – or so I, and other companies, unknowingly thought. At this juncture in my life, a tumultuous journey through the Oil Patch begins.
1.1 Mysteries, Clues and Possibilities.
As a young man, I had dreaded the idea of forever making incremental improvements to aircraft systems, merely as a mainstay to the art of survival and paying the mortgage, sitting at the same desk, in the same building, for decades on end. That possibility, I believed, was a fate worse than death. Thus, in that defining year, I would answer a Schlumberger employment advertisement in The New York Times for scientists eager to change the world – the petroleum world, anyway. But unconvinced that any normal company would hire an inexperienced aerospace engineer, and of all things, for a position chartered with high-tech underground endeavors, I was unwilling to give up one of my ten valuable, hard-earned vacation days for a job interview doomed to fail. Still, the company was stubborn in its pursuit and, for better or worse, kindly accommodated my needs.
Carl Buchholz, the division president at the time, interviewed me that one fateful Saturday. “What do you know about oil?” he bluntly asked, giving me that honest Texan look in the eye. To be truthful, I did not know anything, zilch. “Nothing, but I’ve watched Jed Clampett shoot it out of the ground,” I confessed (Clampett was the hillbilly in the television sitcom who blasted his rifle into the ground, struck oil and moved to Los Angeles to settle in his new mansion in “The Beverly Hillbillies”). Buchholz broke out in uncontrolled laughter. That type of honesty he appreciated. I got the job. And with that, I became Schlumberger’s Supervisor, MWD Telemetry, for 2nd generation mud siren and turbine design.
The company’s Analysts division, at the time responsible for an ambitious next-generation, high-data-rate MWD design program, had built ultra-modern office and flow loop facilities in southwest Houston. The metal pipe test section was housed in an air-conditioned room where engineers could work in a clean and comfortable environment away from the pulsations of the indoor mudpump that supplied our flow. A small section of the flow loop was accessible in this laboratory with the main plumbing carefully hidden behind a wall – details no self-respecting, white-collar Ph.D. cared for nor admitted an interest to.
My charter was simple. We were transmitting at 3 bits/sec in holes shallow by today’s standards with a 12 Hz carrier frequency. Our objective was N bits/sec, where N >> 3 (the value of N is proprietary). The solution seemed straightforward, as company managers and university experts would have it. Simply “crank up the carrier to (N/3) × 12 Hz and run.” I did that. But my transducers would measure only confusion, with new pressure oscillations randomly adding to old ones and results depending on mud type, pump speed and time of day. What happened “behind the wall” controlled what we observed but we were too naïve to know. Anecdotal stories told by different field hands about new prototypes were confusing and contradictory. One simply did not know what to believe. Thirty years later, the data rate is still comparable, a bit better under ideal conditions, as it was then. Clearly, there were physical principles that we did not, or perhaps were never meant to, fully comprehend.
Fast-forward to 1992 at Halliburton Energy Services, an eternity later, where I had been hired as Manager, FasTalk MWD. Again, mass confusion prevailed. Some field engineers had reported excellent telemetry results in certain holes, while others had reported poor performance under seemingly identical conditions. The company had acquired several small companies during that reign of corporate acquisitions in the oil service industry. It would turn out that “good versus bad” depended, with all other variables constant, on whether the signal valve was a “positive” or a “negative” pulser. No one really distinguished between the two: because the MWD valve was simply viewed as a piston located at the end of the drillpipe, exciting the drilling fluid column residing immediately above, it didn’t matter if it was pushing or pulling.
Sirens were a different animal; no one, except Schlumberger, it seemed, understood them. But nobody really did. Additional dependencies on drilling conditions only added to the confusion. Industry consensus at the time held that MWD telemetry characteristics depended on drillbit type and nozzle size and, perhaps, rock properties, to some extent. It also appeared that whether or not the drillbit was off-bottom mattered. Very often, common sense dictated that the drillbit acted as a solid reflector, since nozzle cross-sectional areas were “pretty small” compared to pipe dimensions. Yet, this line of reasoning was contradictory and had its flaws; strong MWD signals by then had been routinely detected in the borehole annulus, where their existence or lack of was used to infer gas influx. It became clear that what the human eye visually perceived as small may not be small from a propagating wave’s perspective.
Lack of controlled experiments also pervaded the industry and still does. Whenever any service company design team was lucky enough to find a test well, courtesy of obliging operating company customers, engineering “control” usually meant installing the same pressure transducer in the same position on the standpipe. New tools that were tested in one field situation would perform completely differently in others: standpipe measurements had lives of their own, it seemed, except at very low data rates of 1 bit/sec or less, barring mechanical tool failure, which was often. Details related to surface plumbing, bottomhole assembly, bit-box geometry, drilling motor details and annular dimensions, were not recorded and were routinely ignored. The simple “piston at the end of pipe model” didn’t care – and neither did most engineers and design teams.
By the mid-1990s, the fact that higher data rate signaling just might depend on wave propagation dawned upon industry practitioners. This revelation arose in part from wave-equation-based seismics – new then, not quite understood, but successful. I began to view my confusion as a source of inspiration. The changing patterns of crests and troughs I had measured had to represent waves – waves whose properties had to depend on mud sound speed and flow loop geometry. At Halliburton, I would obtain patents teaching how to optimize signals by taking advantage of wave propagation, e.g., signal strength increase by downhole constructive wave interference (without incurring erosion and power penalties), multiple transducer array signal processing to filter unwanted signals based on direction and not frequency, and others.
Still, the future of mud pulse telemetry was uncertain, confronting an unknowing fate – a technology held hostage by still more uncontrolled experiments and their dangerous implications. At the time, industry experts had concluded that mud pulse telemetry’s technology limits had been attained and that no increases in data rate would be forthcoming. At Louisiana State University’s ten-thousand-feet flow loop, researchers had carefully increased MWD signal frequencies from 1 to 25 Hz, and measured, to their dismay, continually decreasing pressures at a second faraway receiver location. At approximately 25 Hz, the signal disappeared. Completely.
That result was confirmed by yours truly, at the same facility, using a slightly different pulser system. Enough said – the story was over. Our MWD research efforts were terminated in 1995 and I resigned from the company in 1999. The key revelation would come years later as I watched children play “jump rope” in the park. A first child would hold one end of the rope, while a second would shake the opposing end at a given frequency. Transverse waves on a rope are easy to visualize, but the ideas apply equally to longitudinal waves. The main point is this. At any given frequency, a standing wave system with nodes and antinodes is created that depends on material properties. If the frequency changes, the nodal pattern changes and moves. If one fixes his attention at one specific location, the peak-to-peak displacement appears to come and go. Node and anti-node positions move: what may be interpreted as attenuation may in fact be amplitude reduction due to destructive wave interference – a temporary effect that is not thermodynamically irreversible loss.
This was exactly the situation in the 10,000 feet LSU flow loop. At one end is a mudpump whose pistons act like solid reflectors, assuming tight pump seals, while at the opposite end, a reservoir serves as an open-end acoustic reflector. Pressure transducers were located at fixed
