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The main focus of this book is to show the challenges specific to shale hydrocarbon recovery and the practices to overcome these challenges. This book starts with an overview to the technological evolution that led to successful production of shale plays, and the implications of the shale being a source rock for its hydrocarbon recovery. The second chapter presents the operations of well drilling, hydraulic fracturing, and monitoring activities. Chapter 3 provides an overview of the available methods for reserve estimation of shale resources followed by comprehensive coverage of decline curve analysis (DCA). In a departure from the mostly empirical rate-time DCA methods covered in Chapter 3, advanced rate-time-pressure analysis - often referred to as rate transient analysis (RTA) - methods are presented in Chapter 4. Chapter 4 ends with discussing the complications of fluid flow in shale reservoirs and the required modeling improvements.

Shale Hydrocarbon Recovery: Basic Concepts and Reserve Estimation

Chapter 1. Definitions, history, and differentiating characteristics of shale hydrocarbon recovery

In this chapter, the meaning of the term "shale" as a hydrocarbon resource is described. Next, a brief history of shale hydrocarbon recovery is presented and major steps taken to unlock its significant potential are discussed.  As discussed in details in this chapter, most shale reservoirs are petroleum source rocks. The implications of the source rock nature of shale reservoirs for hydrocarbon accumulation and reservoir development is covered by explaining (1) the origin of oil and gas, (2) relative amounts and distribution of source rock resources as compared to conventional reservoirs, and (3) parameters controlling the source rock quality primarily based on the form of containing organic matter and rock pore space. The major learning outcomes of this chapter are therefore: (1) Define the term "shale" in shale hydrocarbon recovery, (2) describe the technological evolutions that led to unlocking shale recovery in the US, (3) identify the implications of the shale as a source rock for its hydrocarbons content and type, areal extent, and recovery approach.

 

Chapter 2. Drilling, completion, and monitoring operations

Drilling and completion of shale wells have a profound influence on well performance and associated reserves. Before introduction of massive fracturing of horizontal wells, it was not technically and economically feasible to produce most shale resources implying reserves were essentially zero. Optimizing the drilling and completion operations require close monitoring of the operation with the aim of improving it. Different monitoring strategies must be adopted to ensure the stimulation fluids are directed to maximize the efficiency of fracturing operation. In this chapter, drilling, completions, and monitoring operations are introduced. By the end of this chapter, the reader will be able to: (1) Describe how well drilling in shale/tight reservoirs differs from the conventional drilling considering well pads, well direction, and zonal isolation. (2) explain the operation of multiple fracturing (and re-fracturing) of horizontal wells and the required equipment, fluids, and proppant. (3) Discuss the methods applied to diagnose the success of hydraulic fracturing treatment including microseismic and fiber-optic temperature and acoustic monitoring.

 

Chapter 3. Reserve estimation through rate-time analysis

In this chapter and the next, the methods for hydrocarbon reserve estimation of shale resources are covered. In this chapter, we first review the basic definitions relevant to resources and reserves, and the available methods for their evaluation. The importance of rate-time analysis techniques (e.g. Arps' decline curve analysis) to estimate shale reserves is clarified. Next, we introduce and apply the most commonly used rate-time analysis methods in shale reserve estimation including, Arps' (exponential, hyperbolic, and harmonic), Stretched exponential, Power law exponential, Duong, and Logistic growth.

Chapter 4. Rate-pressure-time analysis for reserve estimation

In departure from the simple rate-time decline curve analysis (DCA) methods presented in the previous chapter, in this chapter we present the advanced techniques bringing the pressure into the analysis. DCA methods are essentially empirical introduced based on observation of data behavior. While the rate-pressure-time analysis is physics-based and introduced based on solving the fundamental equations governing flow in the reservoir. The rate-pressure-time analysis is often referred to as rate transient analysis (RTA). In this chapter, the fundamentals of RTA as applied to conventional wells is first introduced. Next, log-log analysis procedure are introduced accordingly along with the flowing material balance plot. The analysis is next extended to conventional gas reservoirs.  Adapting the RTA methods to shale wells requires understanding the flow regimes in multi-fractured horizontal wells and their corresponding analysis techniques. As a result, the conventional RTA methods are extended to shale wells by introducing analysis approaches of transient linear flow, transitional flow, and stimulated-reservoir-volume (SRV) flow. The introduced methods are applied to example problems throughout the chapter.