Friday, 25 March 2016

Energy Choices, Energy Problems

Energy Choices, Energy Problems 

The Age of Oil and the Oil Crunch 

World energy use, cost and reserves.
Energy usage in industrialized countries grew with dizzying speed through the mid-20th century, and during this time people came to rely increasingly on oil. Eventually, oil supplies within the borders of industrialized countries could no longer match the demand, and these countries began to import more oil than they produced themselves. Through the 1960s, oil prices remained low (about $1.80 a barrel), so this was not a problem. In 1973, however, a complex tangle of politics and war led the Organization of Petroleum Exporting Countries (OPEC) to limit its oil exports. In the United States, fear of an oil shortage turned to panic, and motorists began lining up at gas stations, in many cases waiting for hours to fill their tanks. The price of oil rose to $18 a barrel, and newspaper headlines proclaimed, “Energy Crisis!” Governments in industrialized countries instituted new rules to encourage oil conservation. During the last two decades of the twentieth century, the oil market stabilized. Since 2004, oil prices rose overall, passing the $147/bbl mark in 2008; but the price collapsed in late 2008 when the Great  Recession hit. More recently, the price has hovered around $100/bbl (figure above a). Will a day come when shortages arise not because of politics or limitations on refining capacity, but because there is no more oil to produce? As highly populous countries such as China and India industrialize, the use of fuels accelerates. To understand the issues involved in predicting the future of energy supplies, we must first classify energy resources. As noted earlier, we call a particular resource renewable if nature can replace it within a short time relative to a human life span (in months or, at most, decades). A resource is non-renewable if nature takes a very long time (hundreds to perhaps millions of years) to replenish it. Oil is a non-renewable resource, in that the rate at which humans consume it far exceeds the rate at which nature replenishes it, so we will inevitably run out of oil. The question is, when?
Historians in the future may refer to our time as the Oil Age because so much of our economy depends on oil. How long will the Oil Age last? A reliable answer to this question is hard to come by, because there is not total agreement on the numbers that go into the calculation, especially as the use of unconventional reserves increases, so estimates vary widely. Geologists estimate that we’ve already used a substantial proportion of our conventional reserves, but that there are still about 850 to 1,350 billion barrels of proven conventional oil reserves (figure above b), meaning reserves that have been documented and are still in the ground. Optimistically, there may be an additional 2,000 billion barrels of unproven conventional reserves, meaning oil that has not yet been found but might exist. Thus, the world possibly holds between 850 and 3,350 billion barrels of conventional oil. Presently, humanity guzzles oil at a rate of about 31 billion barrels per year. At this rate, conventional oil supplies will last until some time between 2050 and 2150, not too far in the future. 
Some geologists argue that the beginning of the end of the Oil Age has begun, because the rate of consumption now exceeds the rate of discovery and in many regions, the rate of production has already started to decrease. The peak of production for a given reserve is called Hubbert’s Peak, after the geologist who first emphasized that the production of reserves must decline because oil is a non-renewable resource. Hubbert’s Peak for the United States appears to have been passed in the 1970s. Some researchers argue that the global peak may occur between 2012 and 2014, but this number remains uncertain, and only time will tell. Conservation approaches, such as increasing the gas mileage of cars and increasing the amount of insulation in buildings, could stretch out supplies and make them last decades longer. 
Of course, the picture of oil reserves changes significantly if unconventional reserves are included in estimates. All told, perhaps 1.5 trillion barrels of oil may be trapped in tar sands, and 3 trillion barrels trapped in oil shale. But wide disagreement remains concerning whether it’s fair to include all of these reserves, because a significant proportion would be so difficult and expensive to access that they may never really be an economical energy source.
Even in the most optimistic scenario, including 3,000 billion bbls of conventional oil and perhaps 3,000 billion bbls of accessible unconventional oil, at current rates of consumption, supplies can last for only another 200 years, so the Oil Age will last a total of about 350 years (figure above c). On a timeline representing the 4,000 years since the construction of the Egyptian pyramids, this looks like a very short blip. We may indeed be living during a unique interval of human history.

Can Other Fossil Fuels Replace Oil? 

As true limits to the oil supply approach, societies are looking first at relatively abundant supplies of other conventional fossil fuels, namely natural gas and coal, as sources of energy (figure above d). Rough estimates suggest that world natural gas reserves may exceed 180 trillion cubic meters, which would provide approximately the same amount of energy as 1.2 trillion barrels of oil. But tapping into this gas supply requires expensive technologies for extraction and transport. Similarly, worldwide coal reserves are estimated to be about 850 trillion tons, which contains approximately the same amount of energy as 11 trillion barrels of oil. But the stated number for coal reserves does not distinguish clearly between accessible (mineable) coal and inaccessible coal, which is too deep to mine. And, as is the case for oil, there are political and environmental consequences to relying on gas or coal.

Environmental Issues of Fossil Fuel Use 

Marine oil spills. These can come from drilling rigs, or from tankers.
Environmental concerns about energy resources begin right at the source. Oil drilling requires substantial equipment, the use of which can damage the land. And as demonstrated by the 2010 Gulf of Mexico offshore well blowout, oil drilling can lead to tragic loss of life and disastrous marine oil spills (Offshore Drilling and the Deepwater  Horizon Disaster). Oil spills from pipelines or trucks sink into the subsurface and contaminate groundwater, and oil spills from ships and tankers create slicks that spread over the sea surface and foul the shoreline (figure above a, b). Coal and uranium mining also scar the land and can lead to the production of acid mine runoff, a dilute solution of sulphuric acid that forms when sulphur-bearing minerals such as pyrite (FeS2) in mines react with rainwater. The runoff enters streams and kills fish and plants. Collapse of underground coal mines may cause the ground surface to sink. 
Numerous air-pollution issues also arise from the burning of fossil fuels, which sends soot, carbon monoxide, sulphur dioxide, nitrous oxide, and unburned hydrocarbons into the air. Coal, for example, commonly contains sulphur, primarily in the form of pyrite, which enters the air as sulphur dioxide (SO2) when coal is burned. This gas combines with rainwater to form dilute sulphuric acid (H2SO4), or acid rain. For this reason, many countries now regulate the amount of sulphur that coal can contain when it is burned. But even if pollutants can be decreased, burning fossil fuels still releases carbon dioxide (CO2) into the atmosphere. As we discuss in Chapter 19, CO2 is a greenhouse gas, so a change in the amount of CO2 in the atmosphere can affect climate. Because of concern about CO2 production, research efforts are under way to develop techniques to capture CO2 at power plants, liquefy it, and pump it into reservoir rocks deep underground. This process is called carbon sequestration. 

Offshore Drilling and the Deepwater  Horizon Disaster

The Deepwater Horizon.  
A substantial proportion of the world’s oil reserves reside in the sedimentary basins that underlie the continental shelves of passive continental margins. To access such reserves, oil companies must build offshore drilling platforms. In water less than 600 m (2,000 ft) deep, companies position fixed platforms on towers resting on the sea floor. In deeper water, semi-submersible platforms float on huge submerged pontoons (figure above a). With these, oil companies can now access fields lying beneath 3 km (10,000 ft) of water. 
North America’s largest offshore fields occur in the passive-margin basin that fringes the coast of the Gulf of Mexico. More than 3,500 platforms operate in the Gulf at present, together yielding up to 1.7 million bbl/day. 
During both onshore and offshore exploration, drillers worry about the possibility of a blowout. A blowout happens when the pressure within a hydrocarbon reserve penetrated by a well exceeds the pressure that drillers had planned for, causing the hydrocarbons (oil and/ or gas) to rush up the well in an uncontrolled manner and burst out of the well at the surface in an oil gusher or gas plume. Blowouts are rare because, although fluids below the ground are under great pressure due to the weight of overlying material, engineers fill the hole with drilling mud with a density greater than that of clear water. The weight of drilling mud can counter the pressure of underground hydrocarbons and hold the fluids underground. But if drillers encounter a bed in which pressures are unexpectedly high, or if they remove the mud before the walls of the well have been sealed with a casing (a pipe, cemented in place by concrete) a blowout may happen. 
A catastrophic blowout occurred on April 20, 2010, when drillers on the Deepwater Horizon, a huge semi-submersible platform leased by BP, were finishing a 5.5-km-long (18,000 ft) hole in 1.5-kmdeep (5,000 ft) water south of Louisiana. Due to a series of errors, the casing was not sufficiently strong when workers began to replace the drilling mud with clear water. Thus the high-pressure, gassy oil in the reservoir that the well had punctured rushed up the drillhole. A backup safety device called a blowout preventer failed, so the gassy oil reached the  platform and sprayed 100 m (328 ft) into the sky. Sparks from electronic gear triggered an explosion, and the platform became a fountain of flame and smoke that killed 11 workers. An armada of fireboats could not douse the conflagration (figure above b), and after 36 hours, the still-burning platform tipped over and sank. 
Robot submersibles sent to the sea floor to investigate found that the twisted mess of bent and ruptured pipes at the well head was billowing oil and gas. On the order of 50,000 to 62,000 bbl/day of hydrocarbons entered the Gulf’s water from the well. Stopping this underwater gusher proved to be an immense challenge, and initial efforts to block the well, or to put a containment dome over the well head, failed. It was not until July 15 that the flow was finally stopped, and not until September 19 that a new relief well intersected the blown well and provided a conduit to pump concrete down to block the original well permanently. All told, about 4.2 million bbl of hydrocarbons contaminated the Gulf from the Deepwater Horizon blowout. The spill was devastating to wetlands, wildlife, and the fishing and tourism industries.

Alternative Energy 

Can nuclear power or hydroelectric power replace oil? Vast supplies of uranium, the fuel of traditional nuclear plants, remain untapped. Further, nuclear engineers have designed alternative plants, powered by breeder reactors, that essentially produce new fuel. But many people view nuclear plants with concern because of issues pertaining to radiation, accidents, terrorism, and waste storage, and these concerns have slowed the industry. A substantial increase in hydroelectric power production is not likely, as most major rivers have already been dammed, and industrialized countries have little appetite for taming any more. Similarly, the growth of geothermal-energy output seems limited. 
Because of the potential problems that might result from relying more on coal, hydroelectric, and nuclear energy, researchers have been increasingly exploring clean energy options (see figure 1 d). One possibility is solar power, and the cost of solar power is steadily decreasing. Unfortunately, technologies for large-scale solar energy do not yet exist.  Similarly, we can turn to wind power for relatively small-scale energy production, but covering the landscape with windmills is not appealing, and since wind production varies with wind speed, so it can’t provide a steady supply that the present-day energy grid requires. Fusion power may be possible some day, but physicists and engineers have not yet figured out a way to harness it. 
Clearly, society will be facing difficult choices in the not-so-distant future about where to obtain energy, and we will need to invest in the research required to discover new alternatives. By 2050, 40% of energy may be from renewable sources. In the near term, conservation can play an important role by diminishing demand for fossil fuels. 
Credits: Stephen Marshak (Essentials of Geology)