We all know what sampling tools are, or at least, think we do. Over the past four decades, oilfield manufacturers have developed these fluid and pressure transient measurement devices into invaluable and versatile well logging instruments. The typical dual or multiprobe tool consists of pumping and observation probes displaced axially along the tool axis along the same azimuth. Single probe tools will pump and measure a "spherical permeability," while dual probe devices will offer horizontal and vertical permeabilities using data from a single angular orientation. Depending on the test method, compressibilities and pore pressures may also be available. In the early 1990s, a "multiprobe" formation tester was introduced by a major service company that was innovative in its design. This tool, consisting of an active "sink probe" and a passive "horizontal" observation probe displaced azimuthally at 180 deg from the sink, would offer predictions for both permeabilities. However, at low mobilities, measured pressure drops at the latter probe were significantly less than those at the sink. The same was true for its "vertical" probe, located several feet away, coincident with the sink azimuth. These limitations reduced the versatility and usefulness of the azimuthal design, substantially decreasing the accuracy of many tester predictions.

During the past decade, several high risk formation testing projects were undertaken at China Oilfield Services Limited. The above limitations would attract COSL’s engineers, who raised several interesting design challenges. "What if three azimuthally displaced probes, each separated by 120 deg from the others, were used?" And further, "What if each probe in the triple multiprobe tool, possibly equipped with different nozzle sizes and shapes, were capable of operating independently from the others?" Obviously, higher pump rates and improved signals would be possible, and importantly, without the loss of pressure resolution that accompanies straddle packer solutions.

Solutions to inverse problems, primarily for kh and kv, are important to formation evaluation. We have developed rapid and accurate, full three-dimensional simulators for steady flows, accelerating our convergence rates using doublet solutions, relaxation methods and invariant embedding principles whenever possible – on Windows i5 machines, we routinely calculate about twenty solutions per second, for a variable cylindrical coordinate mesh system. Rather than seeking analytical permeability solutions, which are approximate at best, we pursued "big data" statistical approaches using synthetically generated test data. For example, thousands of pressure drop versus kh and kv solutions (at any number of probes) can be created in minutes and used to match measured data in real-time. This database can be created beforehand "at the office," or on demand, at any field job, and compared with field measurements. Thus, intelligent analytics can be deployed at rigsites and remote locations, and run by personnel with limited engineering and software expertise.

These issues are addressed and solved in this book, the most recent in John Wiley’s Advances in Petroleum Engineering Series. We emphasize that our new analysis methods, both direct and inverse, and software, apply also to existing "180 degree" tools – petrophysicists will welcome software models that support interactive desktop analyses of conventional measurements which, at the same time, assess the comparative benefits offered by the new triple probe tools. Wide ranges of "180 versus 120 deg" comparisons are also summarized in this volume. From a broader perspective, our final Chapter 10 integrates and generalizes all modeling features conceptualized, developed and validated in the earlier sections, providing a wide suite of features available for immediate petroleum engineering use. Moreover, the final exposition sets the foundation for new innovations in future "azimuthal multiprobe" tools already on the drawing boards. A companion volume, Supercharge, Invasion and Mudcake Growth in Downhole Applications, offered in Wiley-Scrivener’s Petroleum Engineering Handbook Series, deals with supercharge, formation invasion, mud flow, mud cake and reservoir fluid interactions, plus advances in special forward and inverse methods, applicable to conventional testers and improved "vertical probe" designs for the new COSL multiprobe tool. The present book summarizes and adds to recent author advances for "non-azimuthal" methods that are nonetheless new and also state-of-the-art.

Both of our 2021 volumes are essential to modern pressure testing, and we hope that the pair will find permanent places on petroleum engineers’ bookshelves. And just as important, we emphasize that in this time of great uncertainty and low oil prices, one truth prevails: real innovation is needed now more than ever. The authors hope that our books, our new formation tester and our versatile FT-Multiprobe simulator, will help the industry discover and produce natural resources more efficiently – and, that despite the economic realities confronting all of us, the exciting work in this volume, formulated and developed over more than a decade, would provide a pleasant respite from the business of day-to-day living.

Beijing and Houston

The authors wish to thank the management of China Oilfield Services Limited for permission to publish this manuscript. We address multi-probe formation testing, a COSL project recipient of a National Five Year Special Award to develop core technologies for sampling in complex geologies over wide ranges of mobilities and pressures. We also express our gratitude to Yongsheng Xue, Yongchao Chen, Xiaodong Zou, Xiaokang Zhang, Hongxu Shi, Meng Lan and other team members for their R&D and engineering design efforts, highly diligent and comprehensive laboratory testing, and demanding off-site field testing.

We are indebted to Xiaoying Zhuang for her interpretation and translation skills, and usual hard work and perseverance, which have been instrumental in communicating a wide range of engineering and technical ideas to English-speaking audiences over the past decade. And last but not least, we again thank Phil Carmical, Acquisitions Editor and Publisher, for his confidence and faith in our pressure testing activities over the years. In times of economic uncertainty such as ours, it is imperative that "the show must go on" and that oil and gas industry professionals continue to "push the envelope" despite the headwinds. This monograph describes our multi-year, decade-long efforts in a high risk endeavor and we are pleased to present our ideas and new tools to our petroleum engineering colleagues.

Beijing and Houston