The objective of this textbook is to introduce the reader to the fundamentals of applied well test interpretation. The text focuses on the most basic well testing scenario: a single-well test on a well producing a single-phase fluid, from a single-layer, homogeneous reservoir. Although simple, this scenario illustrates most of the elements required for interpretation in more complex scenarios.

Chapter 1 —Introduction to Applied Well Test Analysis opens with an overview of different types of well tests, common applications and objectives in well testing, and alternatives to conventional testing. The chapter continues with a review of reservoir rock and fluid properties and ends with a brief discussion of the effects of graphical scales on data presentation.

Chapter 2 —Fluid Flow in Porous Media covers the assumptions on which the diffusivity equation is based, then introduces the concepts of superposition in space, superposition in time, and radius of investigation. The remainder of the chapter focuses on the applied topics of wellbore damage and stimulation, pseudosteady-state flow, and wellbore storage.

Chapter 3 —Radial Flow Semilog Analysis introduces semilog methods for estimating permeability and skin factor from data in infinite-acting radial flow for both drawdown and buildup tests. The chapter also discusses classical methods of estimating average reservoir pressure using the semilog plot.

Chapter 4 —Log-Log Type Curve Analysis discusses the Gringarten-Bourdet pressure and pressure derivative type curves and the log-log field data plot. The chapter discusses use of the log-log plot to qualitatively evaluate whether or not a well is damaged or stimulated, and to identify wellbore storage and the infinite-acting radial flow period. The chapter covers estimation of permeability, skin factor, and wellbore storage coefficient from the log-log field data plot without using type curves. The chapter closes with a discussion of some common methods used to calculate the logarithmic derivative from field data.

Chapter 5 —Pressure Transient Testing for Gas Wells introduces the real-gas pseudopressure and pseudotime transforms and their normalized counterparts, adjusted pressure and adjusted time, to allow the use of methods developed for slightly compressible liquids to be used for analysis of gas well test data.

Chapter 6 —Flow Regimes and the Diagnostic Plot introduces the common flow regimes and the use of the standard log-log and flow-regime specific diagnostic plots for flow-regime identification. For each flow regime, examples of one or more reservoir models that exhibit the flow regime are given.

Chapter 7 —Bounded Reservoir Behavior covers the most common models of single-layer reservoir behavior. For each model, the flow regimes that may be exhibited and the order in which they occur are discussed.

Chapter 8 —Variable Flow Rate History discusses various methods for treating a variable flow-rate history, from ignoring prior history for short buildups following long drawdowns to deconvolution. The chapter discusses the effects of some common types of boundaries on the shape of the log-log buildup test for different ways of plotting the data. The chapter then provides a spatial interpretation of a variable rate history as a pressure profile in the reservoir. The effects of rate history on a subsequent buildup are discussed, as are the differences between the drawdown and buildup responses for a well in a closed reservoir, a reservoir with a constant-pressure boundary, and a radial composite reservoir. A method for graphing the rate history preceding a buildup along with the pressure response during the buildup is introduced to help distinguish rate-history-induced features in the derivative from those caused by boundaries.

Chapter 9 —Wellbore Phenomena addresses an issue that impacts any well test to one degree or another, yet has received only sporadic attention in the well testing literature. A number of different wellbore phenomena that may affect the shape of the pressure response, such as changing wellbore storage, a rising or falling fluid interface, and completion cleanup, are discussed. In addition, other phenomena that affect the pressure response but have no impact on well productivity (such as pressure fluctuations from earth tides or daily changes in wellhead temperature, gauge problems, or data processing artifacts) are also addressed.

Chapter 10 —Near-Wellbore Phenomena covers phenomena present in the near-wellbore area that do impact the well performance, including geometric skin factor for a perforated completion, a limited-entry or partial penetration completion, or a deviated well, and non-Darcy skin factor for both drawdown and buildup.

Chapter 11 —Well Test Interpretation Workflow presents a recommended workflow (more accurately, a workflow framework or checklist) for well test interpretation. The major steps are the same for virtually any well test interpretation: collect the data, QC the data, identify flow regimes, select a reservoir model, estimate model parameters, and validate the results.

Chapter 12 —Well Test Design Workflow presents a recommended workflow for well test design. As with well test interpretation, the major steps in well test design are the same for most situations: define the test objectives, collect data, estimate unknown reservoir properties, estimate test duration, estimate test flow rate, and determine flow rate sequence

Disclaimer. The phrases “recommended procedure,” “recommended practice,” or other similar phrases refer to procedures or practices recommended by the authors and do not imply endorsement by the Society of Petroleum Engineers.