Oil and Gas in the Energy Mix of the 21st Century
Authors: Fanchi J.R. 
Published: June 2014

Summary
Energy demand is expected to grow over the next century as more countries seek a better quality of life for their citizens. This demand will be met by a global energy mix; the current fossil-fuel-dominated portfolio is undergoing a transition to one that includes a range of fuel types. This paper presents an overview of energy sources available for use in the 21st Century and a prediction of the contribution of hydrocarbon oil and gas to the 21st Century energy mix. It also discusses the implications for petroleum engineering education and the emergence of a new type of energy industry.

Introduction
Price volatility, supply instability, and environmental concerns are motivating changes to the energy mix of the 21st Century. Fossil fuels (e.g., coal, oil, and gas) were the fuels of choice during the last half of the 20th Century. Figs. 1 and 2, which are based on data presented by Schollnberger,1 show the dominance of fossil fuels in the energy mix at the end of the past century.
Fig. 1 shows historical energy consumption in units of quads, a unit of energy that is often used in discussions of global energy because it is comparable in magnitude with global energy values. One quad equals 1 quadrillion Btu or 10 15 Btu in customary units and approximately 10 18 J in SI units. The legend of Fig. 1 gives the sources of energy. Beginning at the bottom of the figure, we see that firewood, coal, oil, natural gas, water, and nuclear energy were the major contributors to energy in the latter half of the 20th Century. Fig. 2 illustrates the dominance of fossil fuels in the energy mix at the end of the century as a percent of total energy consumed. Each percentage distribution shown in Fig. 2 applies to the associated point in time.
This paper presents an overview of energy sources available for use in the 21st Century and a prediction of the contribution of hydrocarbon oil and gas to the energy mix. Refs. 1 through 6 show that many differing predictions are possible and have been published. For analysis, we selected one plausible scenario that covers the time period of interest. This scenario assumes a gradual transition from dominance of fossil fuels in the current energy mix to a mix with a more balanced distribution of energy options.
We present an energy portfolio for the 21st Century, then estimate the corresponding energy distribution as a percentage of total energy consumed. The projected energy portfolio is used as the basis for our calculation of the change in oil and gas demand during the next century relative to the demand in Year 2000. We then discuss implications for petroleum engineering education and the emergence of a new type of energy industry and the corresponding need for a new type of energy engineer.

Energy Options
Today's energy options include fossil fuels, nuclear energy, solar energy, renewable fuels, and alternative sources. Refs. 7 through 11 describe energy sources that are available or are expected to be available during the 21st Century. The following briefly describes several different types of fuels for providing energy.
Fossil fuels are the dominant energy source in the modern global economy, but environmental concerns are motivating change to an energy supply that is clean. Clean energy refers to energy that has little or no detrimental impact on the environment. Natural gas is a source of relatively clean energy. Oil and gas fields are considered conventional sources of natural gas. Two nonconventional sources of natural gas are coalbed methane and gas hydrates.
Coal beds are an abundant source of methane. The presence of methane gas in coal has been well known to coal miners as a safety hazard but is now being viewed as a source of natural gas. Coalbed methane exists as a monomolecular layer on the internal surface of the coal matrix. Its composition is predominantly methane but can also include other constituents, such as ethane, carbon dioxide (CO2), nitrogen, and hydrogen. The gas, which is bound in the micropore structure of the coal bed, is able to diffuse into the natural fracture network when a pressure gradient exists between the matrix and the fracture network. The fracture network in coal beds consists of microfractures called cleats. Gas flows through these microfractures to the production well.
Gas hydrates are chemical complexes that form when one type of molecule completely encloses another type of molecule in a lattice. In the case of gas hydrates, hydrogen-bonded water molecules form a cage-like structure in which mobile molecules of gas are absorbed or bound. Although gas hydrates can be found throughout the world, difficulties in cost-effective production have hampered development of the resource. Gas hydrates generally are considered troublesome in oil- and gasfield operations, but their potential commercial value as a clean energy resource is changing the industry's perception. Their potential as a gas resource arises from the relatively large volume of gas contained in the gas-hydrate complex.