Shale Oil Production Processes

James G. Speight

• Publisher: Gulf Professional Publishing
• Year: 2012
• Print ISBN: 9780124017214
• eBook ISBN: 9780124017498
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Shale Oil represents a huge additional global fossil fuel resource. However, extracting oil from the shale is no simple task; much still needs to be understood to make the process more cost-effective to increase economic flow rates. Clear and rigorous, Oil Shale Production Process will prove useful for those scientists and engineers already engaged in fossil fuel science and technology as well as scientists, non-scientists, engineers, and non-engineers who wish to gain a general overview or update of the science and technology of fossil fuels. Not only does the book discuss the production processes but also provides methods which should reduce environmental footprint by properly addressing: surface mining and extraction processes, in situ conversion process and hydrotreatment.- Covers production processes technologies such as: surface mining and retorting, in Situ Retoring and processes, direct and indirect retorting and hydrotreatment for shale oil- Methods which should reduce environmental footprint- Easy-to-read understand overview of the chemistry, engineering, and technology of shale oil

Chapter 1

Origin and Properties of Oil Shale

1.1 Origin

Oil shale represents a large and mostly untapped hydrocarbon resource. Like tar sand (oil sand in Canada) and coal, oil shale is considered unconventional because oil cannot be produced directly from the resource by sinking a well and pumping. Oil has to be produced thermally from the shale. The organic material contained in the shale is called kerogen, a solid material intimately bound within the mineral matrix (Allred, 1982; Baughman, 1978; Lee, 1996; Scouten, 1990; US DOE, 2004a,b,c; Speight, 2007, 2008, 2013).

Oil shale is distributed widely throughout the world with known deposits in every continent. Oil shale ranging from Cambrian to Tertiary in age occurs in many parts of the world (Table 1.1). Deposits range from small occurrences of little or no economic value to those of enormous size that occupy thousands of square miles and contain many billions of barrels of potentially extractable shale oil. However, petroleum-based crude oil is cheaper to produce today than shale oil because of the additional costs of mining and extracting the energy from oil shale. Because of these higher costs, only a few deposits of oil shale are currently being exploited; in China, Brazil, and Estonia. However, with the continuing decline of petroleum supplies, accompanied by increasing costs of petroleum-based products, oil shale presents an opportunity for supplying some of the fossil energy needs of the world in the future (Andrews, 2006; Bartis et al., 2005; Culbertson and Pitman, 1973).

Table 1.1 Estimate of Oil Shale Reserves (Tons × 10⁶)

Oil shale is not generally regarded as true shale by geologists nor does it contain appreciable quantities of free oil (Scouten, 1990; Speight, 2008). The fracture resistance of all oil shales varies with the organic content of the individual lamina, and fractures preferentially initiate and propagate along the leaner horizontal laminas of the depositional bed.

Oil shale was deposited in a wide variety of environments, including freshwater to saline ponds and lakes, epicontinental marine basins, and related subtidal shelves as well as shallow ponds or lakes associated with coal-forming peat in limnic and coastal swamp depositional environments. These give rise to different oil shale types (Table 1.2) (Hutton, 1987, 1991), and therefore, it is not surprising that oil shales exhibit a wide range of organic and mineral compositions (Mason, 2006; Ots, 2007; Scouten, 1990; Wang et al., 2009). Most oil shale contains organic matter derived from varied types of marine and lacustrine algae, with some debris from land plants, depending on the depositional environment and sediment sources.

Table 1.2 General Classification of Oil Shale

Sedimentary Rocks Nonorganic Organic rich

Humic coal Bitumen-containing Tar sand (oil sand) Oil shale Terrestrial Cannel coal Lacustrine Lamosite Torbanite Marine Kukersite Marinite Tasmanite

Organic matter in the oil shale is a complex mixture and is derived from the carbon-containing remains of algae, spores, pollen, plant cuticle, corky fragments of herbaceous and woody plants, plant resins, and plant waxes, and other cellular remains of lacustrine, marine, and land plants (Dyni, 2003, 2006; Scouten, 1990). These materials are composed chiefly of carbon, hydrogen, oxygen, nitrogen, and sulfur. Generally, the organic matter is unstructured and is best described as amorphous (bituminite)—the origin of which has not been conclusively identified but is theorized to be a mixture of degraded algal or bacterial remains. Other carbon-containing materials such as phosphate and carbonate minerals may also be present, which, although of organic origin, are excluded from the definition of organic matter in oil shale and are considered to be part of the mineral matrix of the oil shale.

Oil shale has often been called high-mineral coal, but nothing can be further from reality. Maturation pathways for coal and kerogen are different, and, in fact, the precursors of the organic matter in oil shale and coal also differ (Durand, 1980; Hunt, 1996; Scouten, 1990; Speight, 2013; Tissot and Welte, 1978). Furthermore, the origin of some of the organic matter in oil shale is obscure because of the lack of recognizable biological structures that would help identify the precursor organisms, unlike the recognizable biological structures in coal (Speight, 2013). Such materials may be of (1) bacterial origin, (2) the product of bacterial degradation of algae, (3) other organic matter, or (4) all of the above.

Furthermore, oil shale does not undergo the maturation process that occurs for petroleum and/or coal but produces the material known as kerogen (Scouten, 1990). However, there are indications that kerogen may be a by-product of the maturation process. The kerogen residue that remains in the oil shale is formed during maturation and is then ejected from the organic matrix because of its insolubility and relative unreactivity under the maturation conditions (Speight, 2007; Chapter 4). Furthermore, the fact that kerogen, under the high-temperature pyrolysis conditions imposed upon it in the laboratory, forms hydrocarbon distillates (albeit with relatively high amounts of nitrogen) does not guarantee that the kerogen of oil shale is a precursor to petroleum.

The thermal maturity of oil shale refers to the degree to which the organic matter has been altered by geothermal heating. If oil shale is heated to the maximum highest temperature—the actual historical temperature to which the shale has been heated is not known with any degree of accuracy and is typically speculative—as may be the case if the oil shale were deeply buried, the organic matter may thermally decompose to form liquids and gas. Under such circumstances, there is highly unfounded speculation (other than high-temperature laboratory experiments) that oil shale sediments can act as the source rocks for petroleum and natural gas.

Moreover, as stated above, the fact that the high-temperature thermal decomposition of kerogen (in the laboratory) gives petroleum-like material is no guarantee that kerogen is or ever was a precursor to petroleum. The implied role of kerogen in petroleum formation is essentially that—implied, but having no conclusive experimental foundation. However, caution is advised in choosing the correct definition of kerogen since there is the distinct possibility that it is one of the by-products of the petroleum generation and maturation processes, and may not be a direct precursor to petroleum.

Petroleum precursors and petroleum are indeed subject to elevated temperatures in the subterranean formations due to the geothermal gradient. Although the geothermal gradient varies from place to place, it is generally in the order of 25°C/km to 30°C/km (15°F/1000 feet or 8°C/1000 feet, i.e., 0.015°F per foot of depth or 0.008°C per foot of depth). This leaves a serious question about whether or not the material has been subjected to temperatures greater than 250°C (>480°F).

Such experimental work is interesting insofar as it shows similar molecular moieties in kerogen and petroleum (thereby confirming similar origins for kerogen and petroleum). However, the absence of geological time in the laboratory is not a reason to increase the temperature and it must be remembered that application of high temperatures (>250°C, <480°F) to a reaction not only increases the rate of reaction (thereby making up for the lack of geological time) but can also change the nature and the chemistry of a reaction. In such a case, the geochemistry is altered. Furthermore, introduction of a pseudo-activation energy in which the activation energy of the kerogen conversion reactions are reduced leaves much to be desired because of the assumption required to develop this pseudo-activation energy equation(s). In fact, not only will the oil window (the oil-producing phase) vary from kerogen-type to kerogen-type, but it is also not valid to use a fixed set of kinetic parameters within each of these groups.

It is claimed that the degree of thermal maturity of an oil shale can be determined in the laboratory by any one of several methods. One method is to observe the changes in the color of the organic matter in samples collected from varied depths—assuming that the organic matter is subjected to geothermal heating (the temperature being a function of depth), the color of the organic matter might be expected to change from a lighter color (at relatively shallow depths) to a darker color (at relatively deep depths). Then, another unknown issue of shifting of the sedimentary strata comes into play.

Suffice it to state that the role played by kerogen in the petroleum maturation process is not fully understood (Durand, 1980; Hunt, 1996; Scouten, 1990; Speight, 2007; Tissot and Welte, 1978). What obviously needs to be addressed more fully in terms of kerogen participation in petroleum generation is the potential to produce petroleum constituents from kerogen by low-temperature processes rather than by processes that involve the use of temperatures greater than 250°C (>480°F) (Burnham and McConaghy, 2006; Speight, 2007).

If such geochemical studies are to be pursued, a thorough investigation is needed to determine the potential for such high temperatures being present during the main phase, or even various phases, of petroleum generation in order to determine whether kerogen is a precursor to petroleum (Speight, 2007).

Finally, much of the work performed on oil shale has referenced the oil shale from the Green River Formation in the western United States. Thus, unless otherwise stated, the shale referenced in the following text is the Green River shale.

1.2 Oil Shale Types

Mixed with a variety of sediments over a lengthy geological time period, shale forms a tough, dense rock ranging in color from light tan to black. Based on its apparent colors, shale may be referred to as black shale or brown shale. Oil shale has also been given various names in different regions. For example, the Ute Indians, on observing outcroppings burst into flames after being hit by lightning, referred to it as the rock that burns.

Thus, it is not surprising that definitions of the types of oil shale can be varied and confusing. It is necessary to qualify the source of the definition and the type of shale that fits within it.

For example, one definition is based on the mineral content of the shale, in which three categories can recognized namely, (1) carbonate-rich oil shale, which contain a high proportion of carbonate minerals (such as calcite and dolomite) and which usually have the organic-rich layers sandwiched between carbonate-rich layers—these shales are hard formations that are resistant to weathering and are difficult to process using mining (ex situ); (2) siliceous oil shales, which are usually dark brown or black. They are deficient in carbonate minerals but plentiful in siliceous minerals (such as quartz, feldspar, clay, chert, and opal)—these shales are not as hard and weather-resistant as the carbonate shales and may be better suited for extraction through mining (ex situ) methods; and (3) cannel oil shales, which are typically dark brown or black and consist of organic matter that completely encloses other mineral grains—these shales are suitable for extraction through mining (ex situ).

However, mineral content aside, it is more common to define oil shale on the basis of their origin and formation as well as the character of their organic content. More specifically, th...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1. Origin and Properties of Oil Shale
• Chapter 2. Oil Shale Resources
• Chapter 3. Kerogen
• Chapter 4. Mining and Retorting
• Chapter 5. In Situ Retorting
• Chapter 6. Refining Shale Oil
• Chapter 7. Environmental Aspects
• Glossary