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

      Preface

      Formation testing, unlike conventional logging methods focused on resistivity, acoustic, nuclear or magnetic resonance approaches, provides direct results as opposed to indirect inferred properties. In sampling, actual in-situ fluids are collected for surface evaluation. And in pressure transient analysis, properties that pertain to production economics like mobility, compressibility, anisotropy and pore pressure are obtained directly from the underlying Darcy flow equations. By and large, the conventional subject matter deals with single, dual and multiprobe tools where pad nozzles are displaced axially relative to each other and along the same azimuth. This being so, idealized spherical “source” or “sink” methods are used in formulating forward and inverse problems.

      Even so, few models have proven useful. An early steady model for spherical flow no longer applies to the lower mobility formations encountered in practice. Later transient models contain complicated Bessel functions and integrals whose effective use in the field is questionable. And then, a rapid, early-time prediction method for “effective permeability” and pore pressure, addressing the low mobility and “not so low” flowline volume limit – while significant in the 1990s and, in fact, invented by the last author, does not address all-important supercharging effects uncovered in recent field-based publications.

Fortunately, progress in source methods has been made, but at such an unusual pace that any presentations at industry meetings would have been rapidly dated. In support of our work, John Wiley & Sons has published our research in three volumes during 2014 – 2019, introducing the latest ideas and techniques to the industry, complete with derivations, equations and software. The present work, our latest formation testing addition to Wiley-Scrivener’s Petroleum Engineering Handbook Series, serves several purposes. While “handbooks” normally refer to summaries of decades-old technologies, this edition is timely because numerous new advances have been made in related and interdependent areas. These include pressure transient analysis, forward and inverse modeling, supercharge, mudcake growth and fluid invasion formulations, and contamination and cleaning multiphase methods – and all during the past two decades by the present authors. While China Oilfield Services Limited (COSL) does manufacture its own conventional single and dual probe tools, it is the availability of our complete suite of software models that allows its tools to be used in many more innovative ways.

      For example, methods are available to predict permeability and pore pressure rapidly from early time data in low mobility formations with strong flowline volume. But what if significant supercharging exists? Most inverse methods require constant flow rate drawdowns. What if this is not possible? And unacceptably, few authors have ever rigorously studied mudcake growth and fluid invasion, which produce the thick cakes responsible for stuck formation testers – the same phenomena associated with supercharge. Nor do they address the thin cakes that wreak havoc on nozzle pad sealing – leakages that would doom any formation testing job. Numerous related questions are treated in this comprehensive volume. And so this handbook, which addresses all of these problems from source model perspectives, provides unified discussions in forward and inverse formation testing analysis, supercharge in pressure evolution and permeability prediction, plus related topics in fluid invasion, mudcake growth and displacement front prediction. It is our hope that this work stimulates continuing research and enhances the innovative use of conventional tools in the field.

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