Synthesis Gas. James G. Speight

the initial estimates of the size of newly discovered oil fields are usually too low. As crude oil and/or natural gas production continues, successive estimates of the ultimate recovery of fields tend to increase. The term reserve growth refers to the typical increases in estimated ultimate recovery that occur as oil fields are developed and produced. Reserve growth has now become an important part of estimating total potential reserves of an individual province or country. As the worldwide crude oil reserves continue to decline, there is the need for the reserve estimates to be more precise through application of the reserve-growth concept. In fact, the concept could be applied even to the so-called undiscovered resources with some qualifications as to the inherent risk (Speight, 2011a, 2014a).

1.2 Typical Energy Sources

      The widespread use of fossil fuels has been one of the most important stimuli of economic growth and has allowed the consumption of energy at a greater rate than it is being replaced and presents an unprecedented risk management problem (Yergin, 1991; Hirsch, 2005; Hirsch et al., 2005; Yergin, 2011). A peak in the production of crude oil will happen, but whether it will occur slowly or abruptly is not certain – given appropriate warnings, the latter is likely to be the case. The adoption of alternate technologies to supplant the deficit in oil production will require a substantial time period on the order of at least 10 to 20 years.

      Global energy consumption is increasing and is expected to rise by 41% over the period to 2035 – compared to a 52% rise over the last 20 years and 30% rise over the last decade. Of the growth in demand, 95% is expected to come from the emerging economies, while energy use in the advanced economies of North America, Europe and Asia as a group is expected to grow only very slowly – and begin to decline in the later years of the forecast period (BP, 2019). The data for reserve estimates indicate that there are sufficient reserves to cover this trend at least to and even beyond 2035. Crude oil and its associate remain the leading fuel and source of chemicals (Speight, 2014a, 2019a).

      For many decades, coal has been the primary feedstock for gasification units but due to recent concerns about the use of fossil fuels and the resulting environmental pollutants, irrespective of the various gas cleaning processes and gasification plant environmental cleanup efforts, there is a move to feedstocks other than coal for gasification processes (Speight, 2013a, 2013b, 2014b). But more pertinent to the present text, the gasification process can also use carbonaceous feedstocks which would otherwise have been discarded and unused, such as waste biomass and other similar biodegradable wastes. Various feedstocks such as biomass, crude oil resids, and other carbonaceous wastes can be used to their fullest potential. In fact, the refining industry has seen fit to use crude oil resid gasification as a source of hydrogen for the past several decades (Speight, 2014a).

      Gasification processes can accept a variety of feedstocks but the reactor must be selected on the basis of feedstock properties and behavior in the process. The advantage of the gasification process when a carbonaceous feedstock (a feedstock containing carbon) or hydrocarbonaceous feedstock (a feedstock containing carbon and hydrogen) is employed is that the product of focus – synthesis gas – is potentially more useful as an energy source and results in an overall cleaner process. The production of synthesis gas is a more efficient production of an energy source than, say, the direct combustion of the original feedstock because synthesis gas can be (i) combusted at higher temperatures, (ii) used in fuel cells, (iii) used to produce methanol, (iv) used as a source of hydrogen, and (v) particularly because the synthesis gas can be converted via the Fischer-Tropsch process into a range of synthesis liquid fuels suitable for use gasoline engines, for diesel engines, or for wax production.

Therefore, a brief comment about each of the potential energy sources is presented below.

      1.2.1 Natural Gas and Natural Gas Hydrates

      It is rare that crude oil and also heavy crude oil do not occur without an accompanying cover of gas (Speight, 2014a, 2019b). It is therefore important, when describing reserves of crude oil, to also acknowledge the occurrence, properties, and character of the natural gas. In recent years, natural gas has gained popularity among a variety of industrial sectors. Natural gas burns cleaner than coal or crude oil, thus providing environmental benefits. Natural gas is distributed mainly via pipeline, and some in a liquid phase (LNG) transported across oceans by tanker.

      Assuming that the current level of natural gas consumption for the world is maintained, the reserve would be enough to last for another 64 years. However, in this estimation of natural gas longevity, factors such as the increase in annual consumption, the discovery of new reservoirs, and advances in discovery/recovery technology, and utilization of natural gas hydrates are not included. As a result of discoveries of gas in tight shale formations – which has offset more than the annual consumption – the world reserves of natural gas have been in a generally upward trend, due to discoveries of major natural gas fields.

      Natural gas liquids (NGLs) – which are the higher-boiling constituents of natural gas separated from natural gas at a gas processing plant, and include ethane, propane, butane, and pentanes – have taken on a new prominence as shale gas production has increased and prices have fallen (Ratner and Tiemann, 2014). As a result, most producers are accepting the challenges with the opportunism and have shifted production to tight formations, such as the Bakken formation in North Dakota and Montana, to capitalize on the occurrence of natural gas liquids in shale gas development (Speight, 2013f; Sandrea, 2014; Speight, 2015a).

      Methane hydrates (also often referred to as methane clathrates) is a resource in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice (Chapter 1) (Collett, 2009). Methane hydrates exist as methane (the chief constituent of natural gas) trapped in a cage-like lattice of ice which, if either warmed or depressurized (with suitable caution), revert back to water and natural gas. When brought to the surface of the Earth, one cubic meter of gas hydrate releases 164 cubic meters of natural gas.

      Gas hydrates occur in two discrete geological situations: (i) marine shelf sediments and (ii) on-shore Polar Regions beneath permafrost (Kvenvolden 1993; Kvenvolden and Lorenson, 2000). These two Hydrates occur in these two types of settings because these are the settings where the pressure-temperature conditions are within the hydrate stability field (Lerche and Bagirov, 1998). Gas hydrates can be detected seismically as well as by well logs (Goldberg and Saito, 1998; Hornbach et al., 2003).

When drilling in crude oil-bearing and gas-bearing formations submerged in deep water, the reservoir gas may flow into the well bore and form gas hydrates owing to the low temperatures and high pressures found during deep water drilling. The gas hydrates may then flow upward with drilling mud or other discharged fluids. When the hydrates rise, the pressure in the annulus decreases and the hydrates dissociate into gas and water. The rapid gas expansion ejects fluid from the well, reducing the pressure further, which leads to more hydrate dissociation and further fluid ejection.

      1.2.2 The Crude Oil Family

      Crude oil and the equivalent term petroleum, cover a wide assortment of materials consisting of mixtures of hydrocarbon derivatives and other compounds containing variable amounts of sulfur, nitrogen, and oxygen, which may vary widely in volatility, specific gravity, and viscosity. Metal-containing constituents, notably those compounds that contain vanadium and nickel, usually occur in the more viscous crude oils in amounts up to several thousand parts per million and can have serious consequences during processing of these feedstocks. Because crude oil is a mixture of widely varying constituents and proportions, its physical properties also vary widely and the color from colorless to black. The crude oil family consists of various types of crude oil: (i) conventional crude oil, (ii) crude oil from tight formations, (iii) opportunity crude oils, (iv) high acid crude oil, (v) foamy oil, (vi) eavy crude oil.

      The total amount of crude oil is indeed finite, and, therefore, production will one day reach a peak and then begin to decline. This is common sense, as explained in the resource depletion theory which, in this case, assumes that reserves of crude oil