Predominent Energy Sources for Our Energy-Hungry Planet
Carbon-based energy sources have long been and will remain a primary source of energy for our global economy for decades to come. Oil or petroleum (a naturally occurring mixture consisting of hydrocarbons in the gaseous, liquid, or solid phase which may also contain non-hydrocarbons, of which common examples are carbon dioxide, nitrogen, hydrocarbon sulfide and sulfur), is one of the primary carbon-based energy sources consumed by our global economy. Gas is the cleanest burning conventional source of energy accounting for close to a quarter of global consumption.
Africa is believed to currently supply about 12 % of the world’s oil, with untapped reserves of approximately 132.4 trillion barrels, or 8 % of proven reserves globally. According to a report by PriceWaterhouseCoopers (2012), the continent has natural gas reserves of 513.2 trillion cubic feet, or 7 % of the world’s supply.
Rich in hydrocarbons or chains of carbon and hydrogen atoms, conventional crude oil or petroleum is normally extracted from the Earth’s crust by drilling into reservoirs of petroleum. Naturally occurring pressure surrounding the oil reservoirs allows the petroleum to flow to the surface where it is collected and then refined and distilled into valuable products including gasoline, diesel fuel and plastics. To offset pressure declines as the oil is released, techniques including water and gas injections are applied to sustain oil recovery.
With demand continuing to grow for petroleum, one alternative oil source has become increasingly economically viable since the 1960s – “oil sand” or “oil sands,” also referred to as “tar sands” or “extra-heavy oil.” Whatever the name, this oil source is more correctly known as “bitumen.”
Oil Sands in Canada
At the present time, only Canada has a large-scale commercial oil sand industry. Other oil sand deposits exist, including Venezuela. Significant concentrations of petroleum are also locked up in “oil shale” deposits scattered around the world.
An enormous deposit of bitumen or oil sand is found in the Athabasca, Peace River and Wabasca areas of northeastern Alberta province in Canada.
Similar in appearance, texture and aroma to fresh asphalt used for road construction, Canada’s oil sand appears to be the remains of fats in marine algae and other aquatic plants that were buried with sediment millions of years ago.
Conversion of the fat-rich organic matter to hydrocarbon molecule chains begins immediately after sedimentation, aided by microbes. Over time, and subjected to geologic processes resulting in greater depth, temperature and pressure, the original organic material was transformed into oil and gas and bitumen deposits.
Geologists estimate Canada’s oil sand deposits contain in excess of one trillion barrels of bitumen or about 85 percent of the world’s total reserves.
Oil Sand Processing
Whereas petroleum is primarily extracted via wells bored into the Earth’s crust, oil sand is primarily mined or dug with the help of large excavators.
The oil sand mining process begins with removal of the original arboreal forest and its organic-rich soil and sub-soil overburden. The soil and sub-soil consisting of barren, water-laden clay and sand, is carefully set aside and banked for eventual return to its original location and topographical contours after the bitumen deposits have been removed.
The oil sand itself is 40 to 60 meters thick, perched atop a flat limestone formation.
After excavation, hot water and caustic soda is added to the bitumen-rich sand, and the resulting slurry is piped to an extraction operation where it is agitated and injected with air bubbles, resulting in black oil being carried to the top where it can be skimmed off.
The bitumen then undergoes refining processes that result in a synthetic crude oil that will further undergo more refinement and chemical transformations into various petroleum products.
About two tons of oil sand is needed to produce one barrel – about 1/8th of a ton – of oil. Most of the bitumen that saturates the oil sand – about 75 percent – is recoverable using current processes.
After the oil has been extracted from the oil sand, the spent sand is returned to the extraction zone, followed by careful replacement of the sub-soil and then the organic soil that was first removed to obtain the bitumen. Naturally occurring plants and trees are then planted to help restore the original eco-system. Over time, the mined zone regains virtually all of its former diversity, including animal life, as a naturally self-sustaining eco-system.
Other bitumen-extracting processes besides mining with excavators and trucks include cold-flow pumping of fluid bitumen reservoirs and steam-assisted gravity drainage involving steam injection to separate the bitumen from the sand deep underground, followed by pumping of the accumulating bitumen that results from that application of heat energy.
What Is Oil Shale?
The term oil shale generally refers to any sedimentary rock that contains solid bituminous materials (called kerogen) that are released as petroleum-like liquids when the rock is heated in the chemical process of pyrolysis. Oil shale was formed millions of years ago by deposition of silt and organic debris on lake beds and sea bottoms. Over long periods of time, heat and pressure transformed the materials into oil shale in a process similar to the process that forms oil; however, the heat and pressure were not as great. Oil shale generally contains enough oil that it will burn without any additional processing, and it is known as “the rock that burns”.
Oil shale can be mined and processed to generate oil similar to oil pumped from conventional oil wells; however, extracting oil from oil shale is more complex than conventional oil recovery. Extracting oil from oil shale requires conversion of the solid hydrocarbons in the rock to liquid form, so that they can pumped or processed. This is done by heating the rock to a high temperature, and separating and collecting of the resultant liquid. This heating process is called retorting. Oil shale processing and is generally done in one of two ways: surface retorting and in-situ retorting.
Oil Shale Resources in the U.S.
While oil shale is found in many places worldwide, by far the largest deposits in the world are found in the United States in the Green River Formation, which covers portions of Colorado, Utah, and Wyoming. Estimates of the oil resource in place within the Green River Formation range from 1.2 to 1.8 trillion barrels. Not all resources in place are recoverable; however, even a moderate estimate of 800 billion barrels of recoverable oil from oil shale in the Green River Formation is three times greater than the proven oil reserves of Saudi Arabia. Present U.S. demand for petroleum products is about 20 million barrels per day. If oil shale could be used to meet a quarter of that demand, the estimated 800 billion barrels of recoverable oil from the Green River Formation would last for more than 400 years.
More than 70% of the total oil shale acreage in the Green River Formation, including the richest and thickest oil shale deposits, is under federally owned and managed lands. Thus, the federal government directly controls access to the most commercially attractive portions of the oil shale resource base.