Maxwell’s Equations

Groundwater, hydraulic fracturing fluids, and methane gas can more easily flow through the net-work of fractures. Because hydraulic fracturing generally enlarges preexisting fractures in addition to creating new fractures, this network of natural fractures is very important to the extraction of methane from the coal.

1.3.4 B^iogeniC g^aS

Biogenic gas (predominantly methane) is produced by certain types of bacteria (methanogens) dur-ing the process of breakdur-ing down organic matter in an oxygen-free environment (Speight, 2011b).

Thus, biogenic gas is created by methanogenic organisms in marches, bogs, landfills, and shallow sediments. On the other hand, as a point of differentiation, thermogenic gas is created from buried organic material deeper in the earth, at greater temperature and pressure. Livestock manure, food waste, and sewage are all potential sources of biogenic gas, or biogas, which is usually considered a form of renewable energy. Small-scale biogas production is a well-established technology in parts of the developing world, particularly Asia, where farmers collect animal manure in vats and capture the methane given off while it decays.

Landfills offer another underutilized source of biogas (Speight, 2011b). When municipal waste is buried in a landfill, bacteria break down the organic material contained in garbage such as newspa-pers, cardboard, and food waste, producing gases such as carbon dioxide and methane. Rather than allowing these gases to go into the atmosphere, where they contribute to global warming, landfill gas facilities can capture them, separate the methane, and combust it to generate electricity, heat, or both.

The chemical composition of a residuum is complex. Physical methods of fractionation usually indicate high proportions of asphaltenes and resins, even in amounts up to 50% (or higher) of the residuum. In addition, the presence of ash-forming metallic constituents, including such organome-tallic compounds as those of vanadium and nickel, is also a distinguishing feature of residua and the heavier oils. Furthermore, the deeper the cut into the crude oil, the greater is the concentration of sulfur and metals in the residuum and the greater the deterioration in physical properties.

1.4.2 a^SPHalt

Asphalt is manufactured from petroleum (Figure 1.5) and is a black or brown material that has a consistency varying from a viscous liquid to a glassy solid (Speight, 2015c). To a point, asphalt may resemble tar sand bitumen, hence the tendency to refer to bitumen (incorrectly) as “native asphalt.” It is recommended that there be differentiation between asphalt (manufactured) and bitu-men (naturally occurring) other than by the use of the qualifying terms “petroleum” and “native”

since the origins of the materials may be reflected in the resulting physicochemical properties of the

Air Feedstock

Flasher Gas oil

Oxidized asphalt

Cutback asphalt

Solvent

Vacuum-reduced asphalt Oxidizer

FIGURE 1.5 Simplified representation of asphalt production.

Atmos. pipe still

Atmos. distillates 650°F^–

Vacuum gas oil 650°F–1050°F

Vacuum resid.

1050°F⁺ Crude

Atmos.

resid.

650°F⁺

Vacuum pipe still FIGURE 1.4 Simplified crude oil distillation scheme.

two types of materials. It is also necessary to distinguish between the asphalt that originates from petroleum by refining and the product in which the source of the asphalt is a material other than petroleum, for example, wurtzilite asphalt. In the absence of a qualifying word, it is assumed that the term “asphalt” refers to the product manufactured from petroleum.

When the asphalt is produced simply by distillation of an asphaltic crude oil, the product can be referred to as “residual asphalt” or “straight-run asphalt.” If the asphalt is prepared by solvent extrac-tion of residua or by light hydrocarbon (propane) precipitaextrac-tion, or if blown or otherwise treated, the term should be modified accordingly to qualify the product (e.g., propane asphalt, blown asphalt).

Asphalt softens when heated and is elastic under certain conditions. The mechanical proper-ties of asphalt are of particular significance when it is used as a binder or adhesive. The principal application of asphalt is in road surfacing, which may be done in a variety of ways. Light oil dust layer treatments may be built up by repetition to form a hard surface, or a granular aggregate may be added to an asphalt coat, or earth materials from the road surface itself may be mixed with the asphalt.

Other important applications of asphalt include canal and reservoir linings, dam facings, and sea works. The asphalt so used may be a thin, sprayed membrane, covered with earth for pro-tection against weathering and mechanical damage, or thicker surfaces, often including riprap (crushed rock). Asphalt is also used for roofs, coatings, floor tiles, soundproofing, waterproofing, and other building construction elements as well as in a number of industrial products, such as bat-teries. For certain applications, an asphaltic emulsion is prepared in which fine globules of asphalt are suspended in water.

1.4.3 S^yntHetiC C^rude o^il

Coal, oil shale, and tar sand bitumen can be upgraded (converted) through thermal decomposition by a variety of processes to produce a marketable and transportable product. Typically, the product of the conversion (synthetic crude oil) contains very few constituents that passed unchanged from the source (coal, oil shale, and tar sand bitumen) into the product (synthetic crude oil).

The synthetic crude oil so produced varies in nature, but the principal product is a hydrocarbon mixture that may resemble (but not always resembles) conventional crude oil, hence the use of the terms “synthetic crude oil” and “syncrude.” However, the synthetic crude oil, although it may be produced from one of the less conventional conversion processes, can actually be refined by the usual refinery system, with or without some modification to the refinery process(es). For example, in the current and modern context, tar sand bitumen is recovered commercially from the tar sand deposits of northeastern Alberta (Canada) by mining followed by a hot water process for separation of the sand and bitumen after which the bitumen is upgraded by a combination of a thermal or hydro-thermal process followed by product hydrotreating to produce a low-sulfur hydrocarbon-containing synthetic crude oil (Speight, 1995, 2013c, 2014a). By comparison, the unrefined synthetic crude oil from bitumen will generally resemble petroleum more closely than either the synthetic crude oil from coal or the synthetic crude oil from oil shale. Unrefined synthetic crude oil from coal can be identified by a high content of phenolic compounds whereas the unrefined synthetic crude oil from oil shale will contain high proportions of nitrogen-containing compounds (Scouten, 1990; Lee, 1991; Speight, 1995, 2013a,c).

Coal liquids, which are the products produced from the thermal decomposition of coal, also fall into the category of synthetic crude oil, whether the liquids have been hydrotreated or not (Speight, 2013a). The composition can vary from a mixture majority of hydrocarbon species to a mixture con-taining a majority of heteroatom species. Predominant heteroatom species contain oxygen, usually in the form of phenolic oxygen (e.g., C₆H₅OH) or ether oxygen (R₁OR₂).

The refined (hydrotreated) coal liquids, in which the heteroatom content has been reduced to acceptable levels, may also be referred to as synthetic crude oil that is sent to a refinery for further processing into various products.

1.4.4 SHale oil

Shale oil is produced from a special class of bituminous rocks that has achieved some importance (Scouten, 1990; Lee, 1991; Speight, 2012b). These are argillaceous, laminated sediments of gener-ally high organic content that can be thermgener-ally decomposed to yield appreciable amounts of oil, commonly referred to as “shale oil.” Oil shale does not yield shale oil without the application of high temperatures and the ensuing thermal decomposition that is necessary to decompose the organic material (kerogen) in the shale. The kerogen produces a liquid product (shale oil) by thermal decom-position at high temperature (>500°C, >930°F). The raw oil shale can even be used directly as a fuel akin to a low-quality coal. Indeed, oil shale deposits have been exploited as such for several centuries and shale oil has been produced from oil shale since the nineteenth century.

Thus, “oil shale” is the term applied to a class of bituminous rocks that contain a complex hetero-atomic molecule known as “kerogen (q.v.)” and oil shale does not contain oil. Shale oil is produced when kerogen is thermally decomposed to yield appreciable amounts of a hydrocarbon-based oil; it is this product that is commonly referred to as “shale oil.” Oil shale does not yield shale oil without the application of high temperatures and the ensuing thermal decomposition that is necessary to decompose the organic material (kerogen) in the shale. Shale oil also contains heteroatom spe-cies, predominantly organic nitrogen-containing molecules. The refined (hydrotreated) shale oil, in which the heteroatom content has been reduced to acceptable levels, may also be referred to as

“synthetic crude oil” that is sent to a refinery for further processing into various products.