Supercharge, Invasion, and Mudcake Growth in Downhole Applications. Группа авторов

were undertaken at COSL. In the early 1990s, an innovative “multiprobe” formation tester was introduced by a major service company that has greatly benefited the industry. This tool, consisting of an active “sink probe” and a passive “horizontal” observation probe displaced at 180° azimuthally from the sink, would provide measurements for horizontal and vertical permeability. However, in low mobility applications, measured pressure drops at the latter probe were often orders-of-magnitude less than those obtained at the pumping probe. This limitation attracted the interests of COSL engineers, who raised several unusual design challenges. “What if three azimuthally displaced probes, each separated by 120° from the others, were used?” And further, “What if each probe in the triple multiprobe tool were capable of operating independently from the others?”

What would be the logging advantages? What additional parameters of formation evaluation interest could we predict? Is it possible to detect heterogeneities? Dip angle? Can we pump at high rates without releasing dissolved gas? In order to design such a multiprobe tool, a fully three-dimensional transient model would be required to guide mechanical design as well as to support interpretation procedures at the rigsite. Can a rapid, stable, accurate and easy-to-use computational method be devised? Is it possible to develop a robust procedure that supports field work in horizontal and vertical mobility definition? How would we apply “big data” statistical approaches using advanced algorithms? Can inverse procedures be solved accurately and rapidly at the rigsite and in field offices?

      These questions are addressed in a companion 2021 volume in John Wiley’s Advances in Petroleum Engineering series, entitled Multiprobe Pressure Analysis and Interpretation, by Tao Lu, Minggao Zhou, Yongren Feng, Yuqing Yang and Wilson Chin. This complementary volume contains math models entirely different from the present, but which are also applicable to conventional 180° dual probe tools. Both of our 2021 books, drawing on research and engineering developed over more than a decade, are essential to modern formation testing, and we hope that both will find permanent places on petroleum engineers’ bookshelves. In this time of great uncertainty, one truth prevails: now, more than ever, innovation is needed to explore and produce natural resources more efficiently. And innovation in engineering means nothing less than a thorough understanding of physics and mathematics and putting both to important practical use.

      The Authors,

      Beijing and Houston

      Acknowledgements

      The authors wish to thank the management of China Oilfield Services Limited (COSL) for permission to publish this manuscript. Our research efforts hope to advance formation testing, algorithm design and well logging technology and bring greater efficiencies to exploration and production. We are also 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 research activities. In times of economic uncertainty such as ours, it is imperative that “the show must go on” and oil and gas industry professionals continue to “push the envelope” despite the headwinds. This monograph describes our persistent and continuing efforts in this endeavor and we are pleased to present our ideas to our petroleum engineering colleagues.

      1

      Pressure Transient Analysis and Sampling in Formation Testing

      The formation tester is a well logging instrument with extendable pad nozzles which, when pressed against the borehole sandface, extracts in situ formation fluids for delivery to the surface for chemical examination. This process characterizes its fluid “sampling” function. By-products of this operation are pressure transient histories, which can be interrogated using Darcy math models for fluid and formation properties such as permeability, mobility, anisotropy, compressibility and pore pressure. This is referred to as “pressure transient analysis,” or simply, “PTA.” Both can be conducted as wireline or Measurement While Drilling, or “MWD,” applications, where these operations now represent invaluable elements of the standard well logging suite.

      Pressure transient analysis challenges. While collecting and transporting fluids is relatively straightforward, e.g., storing samples in secure vessels that maintain downhole conditions, the PTA process poses a greater design challenge. A well designed tool often begins with a good understanding of the environment, plus physics coupled with sound experience in mathematical modeling. Some ideas are obvious. For example, a single “source” or “sink” probe, serving both pumping and pressure observation functions, will at most provide the “spherical permeability” k_h^2/3k_v/^1/3, where k_h and k_v are horizontal and vertical permeabilities. Thus, “single probe” tools, while mechanically simple, will offer fewer logging advantages than “dual probe” or “multiprobe tools” which provide much greater formation evaluation information.

Figure 1.1. Drawdown-buildup pressure response with dynamic pumping action and flowline.

But how are probe arrays configured and placed for optimal effect? Figures 1.1 and 1.2 illustrate the operation of a single probe tool that withdraws fluid and then stops, creating the expected “drawdown and buildup” shown. If a second probe is desired, should it be placed an axial distance apart but along the same azimuth? Or azimuthally apart, at 180° away along the borehole circumference? What about a “drawdown only” pumpout? Or perhaps, have the pump oscillate sinusoidally in place, thus mimicking the AC transmissions of an electromagnetic logging tool? How many probes are best? What are their flow areas? Do answers to these questions depend on fluid and formation properties?

Figure 1.2. Downhole, surface and logging truck operations.

Background development. The present book addresses these questions for “source” or “sink models” of the pumping nozzle, these terms referring to ideal representations of the flow where borehole and pad geometry are described using mathematically small closed surfaces. The recent books due to Chin et al. (2014) or Formation Testing: Pressure Transient and Contamination Analysis, Chin et al. (2015) or Formation Testing: Low Mobility Pressure Transient Analysis, and Chin (2019) or Formation Testing: Supercharge, Pressure Testing and Contamination Models, published by John Wiley & Sons, contain complete math derivations and detailed validations. However, the rapid pace of recent development suggests a separate volume in Wiley’s Handbook of Petroleum Engineering Series, focused on the main ideas behind the recent works. These ideas are essential as they are also used in the design of newer COSL formation testing tools as well as in interpretation software now available to the petroleum industry. What engineers lack, at present, are job planning and PTA tools both useful at the rigsite and at engineers’ desktops. It is our purpose to support this pressing need.

Figure 1.3. Recent formation