The development of enhanced-oil-recovery (EOR) processes has been ongoing since the end of World War II, when operators who owned reservoirs with declining reserves recognized that significant quantities of oil remained in their reservoirs after primary and secondary recovery (primarily waterflooding). Research and field activity increased as production from major reservoirs declined, worldwide consumption of oil increased, and discoveries of major new reservoirs became infrequent. Intense interest in EOR processes was stimulated in response to the oil embargo of 1973 and the following energy “crisis.” The period of high activity lasted until the collapse of worldwide oil prices in 1986.

Over the years, interest in EOR has been tempered by the increase in oil reserves and production. The discovery of major oil fields in the North Slope of Alaska, the North Sea, regions such as Indonesia and South America, and the Athabasca oil sands of Canada have added large volumes of oil to the worldwide market. The development of horizontal drilling combined with hydraulic fracturing in shale oil reservoirs has added large volumes of light crude oil to the worldwide market. In addition, estimates of reserves from reservoirs in the Middle East increased significantly, leading to the expectation that the oil supply will be plentiful and that the oil price would remain in the vicinity of USD 20 to 25/bbl (constant dollars) for many years.

Although large volumes of oil remain in mature reservoirs, the oil will not be produced in large quantities by EOR processes unless these processes can compete economically with the cost of oil production from conventional sources. Thus, as reservoirs age, a dichotomy exists between the desire to preserve wells for potential EOR processes and the lack of economic incentive because of the existence of large reserves of oil in the world.

Enhanced Oil Recovery describes technologies that can be applied to recover oil that cannot be produced by primary recovery or waterflooding or to recover oil that remains after application of these processes. While many of the technologies were economical at the oil prices that existed in 2013 and most of 2014, they may not be at the oil prices of 2015 through 2017. Development of these processes represents significant technological advances in our understanding of oil recovery from petroleum reservoirs and may be the stimulus for future technological developments.

Approach

This text is written as an introduction to EOR processes, which are processes normally applied after waterflooding. These include polymer, micellar-polymer, and CO₂ flooding and thermal-recovery processes that are typically implemented following primary production. Written for seniors and first-year graduate students in petroleum engineering, we assume that those using this text have a basic understanding of petrophysics (porosity and permeability, saturation), fluid properties (viscosity, density, formation volume factor, and phase behavior), and material balances (volumetrics and elementary depletion calculations). We also assume that students have some grasp of the complexity of reservoirs through exposure to geology courses. These topics can be found in other texts.

We have included three background, or review, chapters that cover microscopic (pore-level)-displacement efficiency, linear-displacement theory, and macroscopic (volumetric) -displacement efficiency, respectively. These chapters can be used by petroleum engineering students for review or by those in other engineering or science disciplines as background information for the study of the different EOR processes treated in the book. The text has been used in a one-semester graduate course in our master’s degree program taken by students majoring in both petroleum and chemical engineering. The text contains more material than can be covered in a one-semester course, allowing the instructor to place more emphasis on some processes than others.

Chapter 1 introduces EOR processes and methods of screening reservoirs that are candidates for potential application. Chapter 2 reviews fundamental concepts for oil recovery from porous rocks at the microscopic or pore scale. Chapter 3 develops linear-displacement theory on the basis of fractional-flow concepts. In Chapter 4, we introduce volumetric-displacement efficiency of processes. Chapter 5 covers polymer flooding, and Chapter 6 introduces miscible-displacement processes, including CO₂ miscible flooding. Chapter 7 presents chemical flooding, and Chapter 8 covers thermal recovery. A number of EOR commercial field applications have been in operation since publication of the first edition and several of these are described in the chapters covering the different processes.

In describing the different EOR processes, we focus on the fundamental concepts of each process. However, we also present methods of predicting oil recovery when the processes are applied to oil reservoirs. Many methods are available to calculate displacement performance, ranging from simple models based on volumetric sweep to sophisticated reservoir simulators. The use of reservoir simulators is beyond the scope of this text. We chose a middle course that reinforces fundamental mechanisms but requires the mathematical skills expected of students taking this as a first course on EOR. In some cases, the computations are tedious, but they can be done easily with short computer programs. Selected programs are included in the Appendices.

While this text was being written, important developments in EOR technology took place in laboratories and oil fields throughout the world. We have included those developments where appropriate. This was possible because we had access to numerous high-quality technical publications prepared by our colleagues in universities and the petroleum industry.

This book began as a comprehensive text on oil-recovery processes authorized by the SPE Textbook Committee. The chapter on waterflooding in the original outline was expanded into the text Waterflooding (published in 1986); writing of this text resumed following completion of Waterflooding. In the years that followed, development of micellar-polymer-flooding technology was phased out as a direct result of the collapse of oil prices in 1986 and the development of new oil supplies throughout the world, which led to projections of oil prices in the vicinity of USD 20 to 25/bbl (in constant dollars) for many years. We attempted to preserve the important parts of this technology in the text, even though at initial writing it appeared unlikely that the technology would be applied for many years.

By 2012, there was a steady rise in oil price from USD 20/bbl when the first edition was prepared to more than USD 100/bbl, which stimulated application of EOR processes throughout the world. The SPE Textbook Committee requested the preparation of a second edition with emphasis on field applications of EOR processes. As the preparation of the second edition was nearing completion, oil prices declined to the vicinity of USD 35 to 50/bbl, as the effect of large volumes of oil produced from horizontal wells impacted the worldwide oil market.

Thermal-recovery processes continue to be the major contributor to production from EOR processes. The chapter on thermal-recovery processes is extensive and could be used for a single course. In Canada, the extensive deposits of tar sands has stimulated the development and application of steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS). These topics have been added to the text.

The development of CO₂ miscible flooding in west Texas created increased application of this process. We have added several field case histories from major reservoirs to the chapter on miscible-displacement processes. There will be continued development and application of this technology in addition to the material covered in this text. We anticipate that a wealth of field case histories will be developed from ongoing projects; therefore, students and instructors should look for additional material as they use the text.

Extensive field application of polymer flooding is occurring in the Daqing field in China, where oil production from polymer flooding is estimated to be in excess of 1.5 Bbbl. Polymer flooding by use of horizontal wells is under development in some heavy-oil reservoirs in Canada.

Although there have been substantial developments in surfactant formulations since the first edition and some pilot field tests, no information was available on field tests. Consequently, the revision of the chapter on chemical flooding focuses primarily on the development and testing of surfactant formulations that are effective over a wide range of reservoir conditions in laboratory tests.

During the past 10 years, laboratory research has demonstrated that waterflood recovery from oil-wet and intermediately wetted cores can be increased by injecting water containing low salinity (Low Sal). Mechanisms contributing to this increase in oil recovery are not well understood and continue to be a major area of research. Although field tests are in progress, the topic of Low Sal is in an early stage of development and is not covered in this revision.