Measurement While Drilling

Signal Analysis, Optimization and Design


Wilson C. Chin, Ph.D., M.I.T.

Stratamagnetic Software, LLC, Houston, Texas

Yinao Su, Limin Sheng, Lin Li, Hailong Bian and Rong Shi

China National Petroleum Corporation (CNPC), Beijing, China

Opening Message

Yinao Su, Ph.D., Academician

Chinese Academy of Engineering, Beijing, China

In modern oil and gas exploration, drilling offers many engineering challenges. Multiple economical objectives are targeted, among them rapid penetration rates and productive payzones. To achieve this, high-data-rate MWD systems are urgently needed for detailed and accurate downhole characterization, real-time information being central to control, optimization and safety. But the downhole environment is not forgiving: high noise levels, strong signal distortion and interference, together with severe attenuation, impede data transmission rate. To overcome these difficulties, completely new systems oriented designs are required to replace simple fixes to existing tools.

Several approaches are available, e.g., electromagnetic wave, intelligent wired pipe and drillpipe acoustics, each possessing its unique shortcomings. Here we have asked, "Is it possible to improve mud pulse telemetry, the most popular and by far least intrusive operationally?" The answer is, "Yes! " We have applied wave propagation principles to hardware development, telemetry design and surface signal processing, treating our challenge from an integrated systems perspective. With research guided by theory and experiment, we have shown that basic transmission rates can be increased significantly, with further improvements possible through data compression.

At China National Petroleum Corporation, through its Drilling Research Institute, new technology, research and innovation aim at responsibly providing society with clean, safe and reliable energy. In this book, we wish to share our experiences with the industry in achieving our goal for "Developing Energy, Creating Harmony." We hope that the methods we have pioneered, described in detail, will contribute to finding oil and gas more safely and efficiently.   


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-data-rate environment is likely to persist.

Through this rapid progress, several disturbing problems are apparent. The first author, having consulted for established as well as start-up companies over the past ten 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 first 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. 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 the 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 of our 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) has 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 also captures the spirit of MWD engineering in China – we have provided recent paper abstracts and described advanced sensor development activities. It is the authors’ hope that the new technologies offered in the following chapters will contribute to the industry’s continuing need and increasing demand for real-time data as deeper, higher potential and more dangerous wells are drilled.

Wilson C. Chin, Ph.D., M.I.T.

Houston, Texas


Phone: (832) 483-6899


The lead author gratefully acknowledges the insights, experiences and friendships he acquired during his early MWD exposure at Schlumberger, Halliburton and other companies – pleasant memories that much more than compensate for the frustrations and sleepless nights brought upon by the challenges of high data rate telemetry. All of the authors are indebted to China National Petroleum Corporation for its support and encouragement throughout this project, and in particular, for its willingness and desire to share its results and activities with the petroleum engineering and well logging community.

Finally, the authors thank Xiaoying "Jenny" Zhuang for her hard work and commitment to ably working both sides of the language barrier (the lead author neither speaks nor reads Chinese, while the CNPC team is newly conversant in English). Without her interpretation skills and willingness to learn and understand MWD design issues, our efforts would not have yielded the successes 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.