Energy of Extraction


The Growth of Unconventional Oil




For the majority of our petroleum history, oil was produced from "conventional" sources, where the oil is extracted on land and requires little more than drilling a hole into the earth.  Just think There Will Be Blood and you will have a good idea of what conventional oil is.  For much of our oil history, these conventional sources have supplied the majority of our petroleum.  Yet the increasingly rapid rate of oil consumption has been paralleled by a rapid reduction in conventional oil reserves.  To compensate for faltering conventional oil, new sources, deemed "unconventional oil",have risen.  These unconventional oil sources, such as oil sands, shale oil, off-shore oil and arctic oil, were previously (and still are) untapped not because they were undiscovered, but because they were too expensive to process.1 The rising price of crude oil has now made these sources economical, so much
so that Canada's tar sands compose over 23% of total U.S. oil imports, the largest single source of foreign oil.
2

Decreasing EROEI: The Approach of 1:1


Why is unconventional oil more expensive than conventional oil?  Unconventional oil has higher costs because more input energy is required to extract the same amount of oil. This can be easily quantized through the use of energy returned on energy invested (EROI).3  EROI is a ratio of the energy output to energy input, or in terms of oil, how many barrels of oil you can extract using the energy contained in one barrel of oil.  In the early days of the U.S. oil industry, crude oil was found by seeing it literally seeping through the ground.  To extract this oil, very little energy was required, so the EROI was about 100:1.3  Like most resources, the oil fields which were found and exploited first were the largest and easiest to access.  As our oil consumption has grown, the production of such fields declined and new fields were thus needed to replace the depleting sources, however replacing these fields was difficult, because the best fields had already been found.  Thus, replacement fields were harder to find and produced less oil.4  As a result, the amount of energy required to extract the oil increased, while the amount of oil found decreased, leading to lower EROIs. 
By 1970, the EROI of U.S. domestic oil had was about even with imported oil (see figure 1). The decline in EROI was mirrored in U.S. oil production, a major factor in the oil crises of 1973, after which the U.S. became heavily reliant on the cheap crude available from abroad.  In 2005, the EROI of domestic oil had dropped to 12:1 and is continuing to decline.  So what does the decline in EROI mean? As EROI drops, more and more oil must be extracted to maintain production levels.  Figure 2 illustrates this point.  Say a source of oil has an EROI (analogous to EROI) of 18.  In order to provide a net supply of 100 units of oil to society, 106 units of total energy must be extracted, with 6 units of power used for the extraction process.  What happens if EROI drops, for example to 1.2?  The effect of such a drop is monstrous. In order to provide the same net amount of energy (100 units), six times as much must be extracted, because 500 units are needed to power the extraction process!  Now this example is assuming that the amount of energy required by society is constant, but in reality it is not.  World oil demand has grown over 36% since 1980.5  So not only is EROI declining, leading to more barrels of oil needed to be extracted for every oil eventually used, but the net amount of barrels of oil required is also increasing, compounding the effect and causing even rapider depletion of oil reserves. Currently
oil from tar sands requires much more input energy than conventional oil.  The energy returned on energy invested (EROI) for refined oil from oil sands is about 2 to 3. For conventional oil, EROI is about 12.6 The higher EROI results in higher costs, more CO2 emissions per mile driven and less net energy output as compared to conventional oil.7 In fact, it has been calculated that at best, shale oil produces similar carbon dioxide emissions as an equivalent amount of lignite, the lowest grade of coal.8

How the Processes Differ: Extraction of Conventional Oil

Conventional oil is extracted by drilling a well through the earth to an oil reservoir.  When the well is first drilled (called the primary recovery stage) the oil reservoir is usually pressurized, due to pressure of the rock sitting above the reservoir, the downward movement of water (which is denser than oil) and the presence of natural gas within the reservoir.  This causes the oil to rise up t thousands of feet to the surface of the earth.9  Since natural forces provide the energy for this migration, little external energy is required.  For this reason the EROI for conventional oil extraction can be up to 40 times higher than the EROI for tar sand oil.7  The recovery factor (what percent of the total oil is recovered) for the primary recovery stage is usually about 5-15%, though it varies greatly from well to well.9

Over the lifetime of the well the pressure within the reservoir begins to drop, slowing the rate at which oil can be produced.  Eventually the pressure decreases to the point at which the pressure is insufficient to force the oil to the surface of the earth.  At this point, secondary recovery techniques are required for further extraction of oil.  External energy is required to force the oil to the surface of the well.  This energy is usually provided using a fluid, such as water, carbon dioxide or natural gas.  The fluid is pumped into the reservoir from a secondary well, pressurizing the reservoir.6  Significant amounts of power are required to force the oil to the surface in a timely manner.  The external energy used in secondary recovery is usually provided by burning fossil fuels, thereby decreasing the EROI of the oil extraction process significantly.  Using secondary recovery techniques allows about 10-15% more oil to be extracted from the reservoir, bringing the total recovery factor to about 30%.

Tertiary recovery techniques can be used to further increase the recovery factor of the oil.  Tertiary recovery techniques  employ heat in the form of steam to raise the temperature of the oil.10 As the temperature of a liquid rises, its viscosity, or stickiness, is reduced.  Thus the steam makes the oil more fluid and easier to extract, allowing for more to flow to the surface. Heating up such vast quantities of petroleum require even more energy input into the system. Again, the energy for this process is provided by fossil fuels and the EROI of tertiary recovery is lowered even more than that of secondary recovery.

Extraction of Tar Sands

Extraction of oil from tar sands differs greatly from the extraction of conventional oil. Indeed the process of extraction resembles strip mining, with huge amounts of material being removed from the surface of the earth. The process uses heavy machinery to remove the ore from the mining site, transferring it to a processing plant. At the plant, the bitumen is extracted from the ore using hot water and agitation. This process can extract 90 to 100% of the bitumen from the ore. It is important to note that two processes are now being used for tar sand oil extraction. The process shown in the video is predominately surface mining, but another process known as "in-situ" extraction. In-situ extraction pumps hot steam and/or water into bitumen deposits too deep to extract via surface mining. the hot fluids decrease the bitumen viscosity, allowing it to be extracted by pumping, like conventional oil. Both of these processes are highly energy intensive, explaining why the EROI mentioned previously is so low.


Extraction of Shale Oil

extraction of shale oil has an even lower EROI than tar sand extraction. This is due to the even higher amounts of processing required to convert the shale oil ore into synthetic oil. This video, being made from a shale oil extraction company, should be viewed with a grain of salt, as many of the figures stated are skewed and give false impressions. For example there are an estimated 1.5 trillion barrels of oil in the Green River Oil formation, however Senator Hatch's implying that "1 trillion barrels" are able to be recovered is hugely inflated. That would assume a 66% recovery rate, almost twice as much as what we can currently extract from conventional oil wells, let alone from oil shale. Also keep an eye out for the amount of processing required before the shale is converted into gasoline, specifically the step which requires "shipping the shale to Canada". This amount of processing is what leads to the incredibly low EROI. Finally, the goal of the company is to generate fifty thousand barrels of oil a day. Yet compared to the U.S. consumption rate of 23 million barrels a day, this is only a drop in the bucket.

Arctic Oil (click here)
Arctic oil is becoming increasingly attractive as conventional sources are depleted. This video gives a good overview of the challenges which face arctic oil extraction, both technically and politically.



Comments